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LT3742 Dual, 2-Phase Step-Down Switching Controller FeaTures
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DescripTion
The LT(R)3742 is a dual step-down DC/DC switching regulator controller that drives high side N-channel power MOSFETs. A 500kHz fixed frequency current mode architecture provides fast transient response with simple loop compensation components and cycle-by-cycle current limiting. The output stages of the two controllers operate 180 out of phase to reduce the input ripple current, minimizing the noise induced on the input supply, and allowing less input capacitance. An internal boost regulator generates a bias rail of VIN + 7V to provide gate drive for the N-channel MOSFETs allowing low dropout and 100% duty cycle operation. The LT3742 can be used for applications where both controllers need to operate independently, or where both controllers are used to provide a single higher current output. The device is available in a thermally enhanced 4mm x 4mm QFN package.
L, LT, LTC, LTM, Linear Technology, the Linear logo, PolyPhase and Burst Mode are registered trademarks and No RSENSE is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners.
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Wide Input Voltage Range: 4V to 30V Wide Output Voltage Range: 0.8V to VIN Low Shutdown IQ: 20A Out-of-Phase Controllers Reduce Required Input Capacitance and Power Supply Induced Noise 0.8V 1.5% Voltage Reference 500kHz Current Mode Fixed Frequency Operation Internal Boost Converter Provides Bias Rail for N-channel MOSFET Gate Drive Power Good Voltage Monitor for Each Output Programmable Soft-Start 24-Lead 4mm x 4mm x 0.75mm Package
applicaTions
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Satellite and Cable TV Set-Top Boxes Distributed Power Regulation Automotive Systems Super Capacitor Charger
Typical applicaTion
8V and 5V Dual Step-Down Converter
VIN 14V 45.3k 1F 20.0k LT3742 VIN 10F VOUT1 8V 4A 47F 200 PG1 RUN1 30k PG1 RUN/SS1 VC1 PG2 RUN/SS2 VC2 GND PG2 20k RUN2 0.010 1.8k 6.5H SW1 SENSE1+ SENSE1- FB1 SW2 SENSE2+ SENSE2- FB2 G1 G2 6.5H 0.010 1.05k 200 VIN 10F VOUT2 5V 4A 47F 50 40 10H 100 4.7F SWB BIAS EFFICIENCY (%) 80 70 60 90 5VOUT
Efficiency vs Load Current
8VOUT
VIN UVLO
0
0.5
1
2.5 3 1.5 2 LOAD CURRENT (A)
3.5
4
3742 TA01b
1nF
1000pF
1000pF
1nF
3742 TA01a
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LT3742 absoluTe MaxiMuM raTings
(Note 1)
pin conFiguraTion
TOP VIEW SENSE1+ SENSE1- SW1 FB1 18 VC1 17 PG1 25 16 RUN/SS1 15 RUN/SS2 14 PG2 13 VC2 7 SW2 8 NC 9 10 11 12 SENSE2+ SENSE2- FB2 NC NC NC
VIN Voltage ................................................................30V UVLO Voltage............................................................30V PG1, PG2 Voltage ......................................................30V SWB, BIAS Voltage ...................................................40V SENSE1+, SENSE2+ Voltage ......................................30V SENSE1-, SENSE2- Voltage ......................................30V RUN/SS1, RUN/SS2 Voltage .......................................6V FB1, FB2 Voltage .........................................................6V VC1, VC2 Voltage ..........................................................6V Junction Temperature ........................................... 125C Operating Junction Temperature Range (Note 2) .................................................. -40C to 125C Storage Temperature Range .................. -65C to 125C
24 23 22 21 20 19 G1 1 VIN 2 UVLO 3 BIAS 4 SWB 5 G2 6
UF PACKAGE 24-LEAD (4mm x 4mm) PLASTIC QFN TJMAX = 125C, JA = 36C/W EXPOSED PAD (PIN 25) IS GND, MUST BE SOLDERED TO PCB
orDer inForMaTion
LEAD FREE FINISH LT3742EUF#PBF TAPE AND REEL LT3742EUF#TRPBF PART MARKING 3742 PACKAGE DESCRIPTION 24-Lead (4mm x 4mm) Plastic QFN TEMPERATURE RANGE -40C to 125C (Note 2) Consult LTC Marketing for parts specified with wider operating temperature ranges. Consult LTC Marketing for information on non-standard lead based finish parts. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
elecTrical characTerisTics
PARAMETER Minimum Operating Input Voltage Quiescent Current Shutdown Current UVLO Pin Threshold UVLO Pin Hysteresis Current RUN/SS Pin Threshold RUN/SS Pin Charge Current FB Pin Voltage FB Pin Voltage Line Regulation
The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = 5V unless otherwise specified.
CONDITIONS VUVLO = 1.5V VRUN/SS1 = VRUN/SS2 = VFB1 = VFB2 = 1V VRUN/SS1 = VRUN/SS2 = 0V UVLO Pin Voltage Rising VUVLO = 1V, Current Flows Into Pin VRUN/SS = 0V
l l l
MIN
TYP 3.5 5.0 20
MAX 4.0 7.0 35 1.28 4 1.5 0.812
UNITS V mA A V A V A V %/V
1.20 1.8 0.2 0.5 0.788
1.25 3 0.5 1 0.800 0.01
VIN = 5V to 30V
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LT3742 elecTrical characTerisTics
PARAMETER FB Pin Bias Current FB Pin Voltage Matching Error Amplifier Transconductance Error Amplifier Voltage Gain VC Pin Source Current VC Pin Sink Current Controller Switching Frequency Switching Phase Maximum Current Sense Voltage Current Sense Matching Current SENSE Pins Total Current Gate Rise Time Gate Fall Time Gate On Voltage (VG - VSW) Gate Off Voltage (VG - VSW) PG Pin Voltage Low Lower PG Trip Level (Relative to VFB) Lower PG Trip Level (Relative to VFB) Upper PG Trip Level (Relative to VFB) Upper PG Trip Level (Relative to VFB) PG Pin Leakage Current PG Pin Sink Current Bias Pin Voltage SWB Pin Current Limit SWB Pin Leakage Current Bias Supply Switching Frequency Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. VSWB = 12V 0.88 VSENSE
- = 3.3V
The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = 5V unless otherwise specified.
CONDITIONS VFB = 0.8V, VC = 0.4V -4 MIN TYP 50 0 250 500 VFB = 0.6V VFB = 1V 440
l
MAX 200 4
UNITS nA mV mho V/V A A
15 15 500 180 50 60 5 -1.0 40 40 60 6.0 6.7 0.4 0.20 -7 -10 7 4 200 VIN + 6.6 250 -10 -13 10 7 0.1 500 VIN + 7 340 0.01 1.0 VIN + 7.7 500 1 1.12 7.0 0.75 0.5 -13 -16 13 10 70 560
kHz Deg mV % mA A ns ns V V V % % % % A A V mA A MHz
Between Controllers SENSE-, SENSE+ = 0V SENSE-, SENSE+ = 3.3V CLOAD = 3300pF CLOAD = 3300pF VBIAS = 12V VBIAS = 12V IPG = 100A VFB Increasing VFB Decreasing VFB Increasing VFB Decreasing VPG = 2V VPG = 0.5V
Note 2: The LT3742E is guaranteed to meet performance specifications from 0C to 125C operating junction temperature range. Specifications over the - 40C to 125C operating junction temperature range are assured by design, characterization and correlation with statistical process controls.
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LT3742 Typical perForMance characTerisTics
IQ-SHDN vs Temperature
50 10 9 8 CURRENT (mA) 7 6 5 4 10 -50 3 -50 -25 50 -50 -25 75 0 25 50 TEMPERATURE (C) 100 125 SENSE VOLTAGE (mV) 50 25 75 0 TEMPERATURE (C) 100 125 40 CURRENT (A) 65
IQ-Running vs Temperature
70
Controller Current Sense Voltage vs Temperature
30
60
20
55
-25
75 0 25 50 TEMPERATURE (C)
100
125
3742 G01
3742 G02
3742 G03
Internal UVLO vs Temperature
5 3.0 2.5 4 2.0 3 UVLO (V)
UVLO Threshold vs Temperature
830 820 810 VFB (mV) 800 790 780
VFB vs Temperature
VIN (V)
1.5 1.0
2 0.5 1 -50 0 -50 -25
-25
75 0 25 50 TEMPERATURE (C)
100
125
50 25 75 0 TEMPERATURE (C)
100
125
770 -50 -25
50 25 75 0 TEMPERATURE (C)
100
125
3742 G04
3742 G05
3742 G06
RUN/SS Current vs Temperature
1.8 3.0
UVLO IHYST vs Temperature
2.8 RUN/SS CURRENT (A) 1.2 IHYST (A) 0.6 2.2 0 -50
2.6
2.4
-25
0 25 50 75 TEMPERATURE (C)
100
125
2.0 -50
-25
50 0 75 25 TEMPERATURE (C)
100
125
3742 G07
3742 G08
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LT3742 Typical perForMance characTerisTics
Controller Frequency vs Temperature
600 1.0
PG Threshold vs Temperature
10
VBIAS - VIN vs Temperature
FEEDBACK VOLTS RISING (V)
550 FREQUENCY (kHz)
0.9 (VBIAS - VIN) (V) 100 125 8
500
0.8
POWER GOOD
6
450
0.7
400 -50
-25
75 0 25 50 TEMPERATURE (C)
100
125
0.6 -50
-25
75 0 25 50 TEMPERATURE (C)
4 -50
-25
75 0 25 50 TEMPERATURE (C)
100
125
3742 G09
3742 G10
3742 G11
SWB Current Limit vs Temperature
380 1.0
RUN/SS Threshold vs Temperature
SWB CURRENT LIMIT (mA)
360 RUN/SS VOLTS (V) -25 75 0 25 50 TEMPERATURE (C) 100 125 0.7
340
0.4
320
300 -50
0.1 -25
0
25 50 75 TEMPERATURE (C)
100
125
3742 G13
3742 G12
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LT3742 pin FuncTions
G1, G2 (Pins 1, 6): Gate Drives. These pins provide high current gate drive for the external N-channel MOSFETs. These pins are the outputs of floating drivers whose voltage swings between the BIAS and SW pins. VIN (Pin 2): Input Voltage. This pin supplies current to the internal circuitry of the LT3742. This pin must be locally bypassed with a capacitor. UVLO (Pin 3): Undervoltage Lockout. Do not leave this pin open ; connect it to VIN if not used. A resistor divider connected to VIN is tied to this pin to program the minimum input voltage at which the LT3742 will operate. When this pin is less than 1.25V, the controllers are disabled (the RUN/SS pins are still used to turn on each switching regulator). Once this pin drops below 1.25V, a 3A current sink draws current into the pin to provide programmable hysteresis for UVLO. BIAS (Pin 4): Bias for Gate Drive. This pin provides a bias voltage higher than the input voltage to drive the external N-channel MOSFETs. The voltage on this pin is regulated to VIN + 7V. SWB (Pin 5): Bias Regulator Switch. This is the collector of an internal NPN switch used to generate the bias voltage to provide gate drive for the external N-channel MOSFETs. RUN/SS1, RUN/SS2 (Pins 16, 15): Run/Soft-Start Pins. These pins are used to shut down each controller. They also provide a soft-start function with the addition of an external capacitor. To shut down any regulator, pull the RUN/SS pin to ground with an open-drain or open-collector device. If neither feature is used, leave these pins unconnected. PG1, PG2 (Pins 17, 14): Power Good. These pins are open-collector outputs of internal comparators. PG remains low until the FB pin is within 90% of the final regulation voltage. As well as indicating output regulation, the PG pins can be used to sequence the switching regulators. The PG outputs are valid when VIN is greater than 4V and either of the RUN/SS pins is high. The power good comparators are disabled in shutdown. If not used, these pins should be left unconnected. VC1, VC2 (Pins 18, 13): Control Voltage and Compensation Pins for Internal Error Amplifiers. Connect a series RC from these pins to ground to compensate each switching regulator loop. FB1, FB2 (Pins 19, 12): Feedback Pins. The LT3742 regulates these pins to 800mV. Connect the feedback resistors to this pin to set the output voltage for each switching regulator. SENSE1-, SENSE2- (Pins 20, 11): Negative Current Sense Inputs. These pins (along with the SENSE+ pins) are used to sense the inductor current for each switching regulator. SENSE1+, SENSE2+ (Pins 21, 10): Positive Current Sense Inputs. These pins (along with the SENSE- pins) are used to sense the inductor current for each switching regulator. SW1, SW2 (Pins 24, 7): Switch Nodes. These pins connect to the source of the external N-channel MOSFETs and to the external inductors and diodes. Exposed Pad (Pin 25): Ground. The Exposed Pad of the package provides both electrical contact to ground and good thermal contact to the printed circuit board. The Exposed Pad must be soldered to the circuit board to ensure proper operation.
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LT3742 block DiagraM
SWB BIAS 25 GND VIN 2 VIN 3 UVLO GATE DRIVE BIAS BOOST REGULATOR 1.25V BIAS 5 4 VIN
+ -
UNDERVOLTAGE LOCKOUT THERMAL SHUTDOWN VREF 1.25V 0.88V 0.80V 0.72V
3A UVLO
ENABLE COMPARATOR 0.5V
INTERNAL SUPPLY ENABLE D Q Q
TO RUN/SS1 RUN/SS2 LT3742 CONTROLLER 1 AND 2 R Q S 500kHz SLAVE OSCILLATOR TO ENABLE COMPARATOR PWM COMPARATOR PHASE SYNC BIAS G GATE DRIVER CURRENT SENSE AMPLIFIER ERROR AMPLIFIER SW VOUT VIN
RUN/SS SHDN
SS
PGOOD
PG POWER GOOD COMPARATORS
+ + -
1A
+ -
+ -
+ + -
ENABLE
1MHz MASTER OSCILLATOR
PHASE SYNC FOR DC/DC CONTROLLERS
+ -
+ -
0.80V
SENSE+ SENSE- FB
VC
0.88V FB
0.72V
3742 BD1
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LT3742 operaTion
The LT3742 is a dual, constant frequency, current mode DC/DC step-down controller. The two controllers in each device share some common circuitry including protection circuitry, the internal bias supply, voltage reference, master oscillator and the gate drive boost regulator. The Block Diagram shows the shared common circuitry and the independent circuitry for both DC/DC controllers. Important protection features included in the LT3742 are undervoltage lockout and thermal shutdown. When either of these conditions exist, the gate drive bias regulator and both DC/DC controllers are disabled and both RUN/SS pins are discharged to 0.5V to get ready for a new soft-start cycle. Undervoltage lockout (UVLO) is programmed using two external resistors. When the UVLO pin drops below 1.25V, a 3A current sink is activated to provide programmable hysteresis for the UVLO function. A separate, less accurate, internal undervoltage lockout will disable the LT3742 when VIN is less than 2.5V. The gate drive boost regulator is enabled when all internal fault conditions have been cleared. This regulator uses both an internal NPN power switch and Schottky diode to generate a voltage at the BIAS pin that is 7V higher than the input voltage. Both DC/DC controllers are disabled until the BIAS voltage has reached ~90% of its final regulation voltage. This ensures that sufficient gate drive to fully enhance the external MOSFETs is present before the driver is allowed to turn on. The master oscillator runs at 1MHz and clocks the gate drive boost regulator at this frequency. The master oscillator also generates two 500kHz clocks, 180 out of phase, for the DC/DC controllers. A power good comparator pulls the PG pin low whenever the FB pin is not within 10% of the 800mV internal reference voltage. PG is the open-collector output of an NPN that is off when the FB pin is in regulation, allowing an external resistor to pull the PG pin high. This power good indication is valid only when the device is enabled (RUN/SS is high) and VIN is 4V or greater. The LT3742 enables each controller independently when its RUN/SS pin is above 0.5V and each controller generates its own soft-start ramp. During start-up, the error amplifier compares the FB pin to the soft-start ramp instead of the precision 800mV reference, which slowly raises the output voltage until it reaches its resistor programmed regulation point. Control of the inductor current is strictly maintained until the output voltage is reached. The LT3742 is ideal for applications where both DC/DC controllers need to operate separately. A pulse from the 500kHz oscillator sets the RS flip-flop and turns on the external N-channel MOSFET. Current in the switch and the external inductor begins to increase. When this current reaches a level determined by the control voltage (VC), the PWM comparator resets the flip-flop, turning off the MOSFET. The current in the inductor then flows through the external Schottky diode and begins to decrease. This cycle begins again at the next set pulse from the slave oscillator. In this way, the voltage at the VC pin controls the current through the inductor to the output. The internal error amplifier regulates the output voltage by continually adjusting the VC pin voltage. Direct control of the peak inductor current on a cycle-by-cycle basis is managed by the current sense amplifier. Because the inductor current is constantly monitored, the devices inherently provide excellent output short-circuit protection.
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LT3742 applicaTions inForMaTion
Soft-Start and Shutdown The RUN/SS (Run/Soft-Start) pins are used to enable each controller independently, and to provide a user-programmable soft-start function that reduces the peak input current and prevents output voltage overshoot during start-up. To disable either controller, pull its RUN/SS pin to ground with an open-drain or open-collector device. If both RUN/SS pins are pulled to ground, the LT3742 is placed in shutdown mode, and quiescent current is reduced to 20A. Internal 1A current sources pull up on each RUN/SS pin, and when either pin reaches 0.5V, that controller is enabled, along with the internal bias supply, gate drive boost regulator, voltage reference and master oscillator. If both outputs are always enabled together, one soft-start capacitor can be used with both RUN/SS pins tied together. The Benefits of Soft-Start When a capacitor is tied from the RUN/SS pin to ground, the internal 1A pull-up current source generates a voltage ramp on this pin. During start-up, the error amplifier
VOUT 5V/DIV
compares the FB pin to this ramp instead of to the 800mV reference; this slowly and smoothly increases the output voltage to its final value, while maintaining control of the inductor current. Always check the inductor current and output voltage waveforms to ensure that the programmed soft-start time is long enough. A new soft-start cycle will be initiated whenever VIN drops low enough to trigger undervoltage lockout (programmed using the UVLO pin), or the LT3742 die temperature exceeds thermal shutdown. A typical value for the soft-start capacitor is 1nF . Soft-start is strongly recommended for all LT3742 applications, as it provides the least amount of stress on the external power MOSFET and catch diode. Without soft-start, both of these components will see the maximum current limit every start-up cycle. Figures 1a and 1b show startup waveforms with and without soft-start for the circuit on the front page. Notice the large inductor current spike and the output voltage overshoot when soft-start is not used. While this may be acceptable for some systems, the addition of a single capacitor dramatically improves the start-up behavior of each DC/DC controller.
VOUT 5V/DIV
IL 2A/DIV
IL 2A/DIV
0.5ms/DIV
3742 F01a
0.5ms/DIV
3742 F01b
Figure 1a. Start-Up Waveforms Without Soft-Start
Figure 1b. Start-Up Waveforms with 1nF Soft-Start Capacitor
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LT3742 applicaTions inForMaTion
Power Good Indicators The PG pin is the open-collector output of an internal window comparator that is pulled low whenever the FB pin is not within 10% of the 800mV internal reference voltage. Tie the PG pin to any supply less than 30V with a pull-up resistor that will supply less than 200A. This pin will be open when the LT3742 is placed in shutdown mode regardless of the voltage at the FB pin. The power good indication is valid only when the LT3742 is enabled (RUN/SS is high) and VIN is 4V or greater. Output Sequencing and Tracking The RUN/SS and PG pins can be used together to sequence the two outputs of the LT3742. Figure 3 shows three circuits to do this. For the first two cases, controller 1 starts first. In Figure 2a, controller 2 turns on only after controller 1 has reached within 10% of its final regulation voltage. A larger value for the soft-start capacitor on RUN/SS2 will provide additional delay between the outputs. One
LT3742 RUN/SS1 SHDN 4.7nF PG1 RUN/SS2 4.7nF
SHDN (REFERENCE) VOUT1 5V/DIV VOUT2 10V/DIV 5ms/DIV
3742 F02a
Figure 2a. Supply Sequencing with Controller 2 Delayed Until After Controller 1 is in Regulation
LT3742 RUN/SS1 SHDN 4.7nF
SHDN (REFERENCE) VOUT1 5V/DIV VOUT2 10V/DIV 5ms/DIV
3742 F02b
RUN/SS2 10nF
Figure 2b. Supply Sequencing with Controller 2 Having a Fixed Delay Relative to Controller 1
LT3742 RUN/SS1 SHDN 10nF
SHDN (REFERENCE) VOUT1 5V/DIV VOUT2 10V/DIV 5ms/DIV
3742 F02c
RUN/SS2
Figure 2c. Both Conditions Start Up Together with Ratiometic Tracking
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LT3742 applicaTions inForMaTion
characteristic to notice about this method is that if the output of controller 1 goes out of regulation enough to trip the power good comparator, controller 2 will be disabled. In Figure 2b, a slightly larger capacitor on RUN/SS2 delays the turn-on of controller 2 with respect to controller 1. The start-up waveforms for this method look very similar to the one shown in Figure 6a, but here controller 2 is not disabled if controller 1 goes out of regulation. In Figure 2c, both RUN/SS pins share a single capacitor and start up at the same time. By sharing the same softstart signal, this method provides ratiometric tracking of the two outputs. Undervoltage Lockout (UVLO) An external resistor divider can be used to accurately set the minimum input voltage at which the LT3742 will operate. Figure 3 shows the basic UVLO operation. Once the UVLO pin drops below 1.25V, an undervoltage lockout event is signaled, turning on a 3A current source to provide hysteresis. During a UVLO event, both controllers and the gate drive boost regulator are disabled. For the LT3742, all RUN/SS pins are discharged to get ready for a new soft-start cycle. For each controller that is enabled, it's RUN/SS pin will be held to 500mV until the input voltage rises above the upper UVLO trip voltage. The UVLO function is only active when one or more of the controllers are enabled using the RUN/SS pin. The UVLO pin can not be used to directly start the part. Do not leave the UVLO pin unconnected; tie it to VIN if not used. A separate, less accurate, internal undervoltage lockout will disable the LT3742 when VIN is less than 2.5V. The UVLO resistor values are chosen to give the desired minimum operating voltage (VIN(MIN)) and the desired amount of hysteresis (VHYST). The LT3742 will turn on when the input voltage is above (VIN(MIN) + VHYST), and once on, will turn off when VIN drops below VIN(MIN). Select the value for RUV1 first, then select the value for RUV2.
RUV1 =
VHYST 3A 1.25V VIN(MIN) - 1.25V
RUV2 = RUV1 *
Input Voltage Range The minimum input voltage is determined by either the LT3742's minimum operating voltage of 4V, UVLO or by the output voltages of a given application. The LT3742 can operate at 100% duty cycle, so if the input voltage drops close to or equal to one of the output voltages, the controller will go into low dropout operation (100% duty cycle). The duty cycle is the fraction of the time the N-channel MOSFET is on every switch cycle, and is determined by the input and output voltages:
V +V DC = OUT D VIN - VDS + VD
where VD is the forward drop of the catch diode (~0.4V) and VDS is the typical MOSFET voltage drop (~0.1V).
+
UVLO
VIN RUV1
VIN
2
1.25V
UVLO
3 3A
-
RUV2
3742 F03
Figure 3. Undervoltage Lockout
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LT3742 applicaTions inForMaTion
The maximum input voltage is determined by the absolute maximum ratings of the VIN and BIAS pins (30V and 40V, respectively) and by the minimum duty cycle, DCMIN = 15%. The Benefits of 2-Phase Operation Traditionally, dual controllers operate with a single phase. This means that both power MOSFETs are turned on at the same time, causing current pulses of up to twice the amplitude of those from a single regulator to be drawn from the input capacitor. These large amplitude pulses increase the RMS current flowing in the input capacitor, require the use of larger and more expensive input capacitors, increase EMI, and causes increased power losses in the input capacitor and input power supply. The two controllers of the LT3742 are guaranteed by design to operate 180 out of phase. This assures that the current in each power MOSFET will never overlap, always presenting a significantly low peak and RMS current demand to the input capacitor. This allows the use of a smaller, less expensive input capacitor, improving EMI performance and real world operating efficiency. Figure 4 shows example waveforms for a single phase dual controller versus a 2-phase LT3742 system. In this case, 5V and 3.3V outputs, each drawing a load current of 2A, are derived from a 12V supply. In this example, 2-phase
2-Phase Dual Controller
V +V VIN(MAX) = OUT D + VSW - VD DCMIN
The formula above calculates the maximum input voltage that allows the part to regulate without pulse-skipping, and is mainly a concern for applications with output voltages lower than 3.3V. For example, for a 2.5V output, the maximum input voltage is:
2.5V + 0.4V VIN(MAX) = + 0.1V - 0.4V = 19V 0.15
If an input voltage higher than 19V is used, the 2.5V output will still regulate correctly, but the part must pulse-skip to do so. Pulse skipping does not damage the LT3742, but it will result in erratic inductor current waveforms and higher peak currents. Note that this is a restriction on the operating input voltage only for a specific output voltage; the circuit will tolerate inputs up to the absolute maximum rating.
Single Phase Dual Controller
SW1 (V)
SW2 (V)
IL1
IL2
IIN
3742 F04
Figure 4. Example Waveforms for a Single Phase Dual Controller vs the 2-Phase LT3742
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LT3742 applicaTions inForMaTion
operation would reduce the RMS input capacitor current from ~1.8ARMS to ~0.8ARMS. While this is an impressive reduction by itself, remember that power losses are proportional to IRMS2, meaning that the actual power wasted due to the input capacitor is reduced by a factor of ~4. Figure 5 shows the reduction in RMS ripple current for a typical application. The reduced input ripple current also means that less power is lost in the input power path. Improvements in both conducted and radiated EMI also directly accrue as a result of the reduced RMS input current and voltage. Significant cost and board footprint savings are also realized by being able to use smaller, less expensive, lower RMS current-rated input capacitors. Of course, the improvement afforded by 2-phase operation is a function of the relative duty cycles of the two controllers, which in turn, are dependent upon the input voltage (DC VOUT/VIN). It can be readily seen that the advantages of 2-phase operation are not limited to a narrow operating range, but in fact extend over a wide region. A good rule of thumb for most applications is that 2-phase operation will reduce the input capacitor requirement to that for just one channel operating at maximum current and 50% duty cycle.
3.0 2.5 INPUT RMS CURRENT (A) 2.0 1.5 1.0 0.5 0 SINGLE PHASE DUAL CONTROLLER
Inductor Value Selection The inductor value directly affects inductor ripple current, IRIPPLE, and maximum output current, IOUT(MAX). Lower ripple current reduces core losses in the inductor, ESR losses in the output capacitors and output voltage ripple. Too large of a value, however, will result in a physically large inductor. A good trade-off is to choose the inductor ripple current to be ~30% of the maximum output current. This will provide a good trade off between the inductor size, maximum output current, and the amount of ripple current. Note that the largest ripple current occurs at the highest the input voltage, so applications with a wide VIN range should consider both VIN(TYP) and VIN(MAX) when calculating the inductor value:
L VIN - VOUT V 1 * OUT * 0.3 * IOUT(MAX) VIN 500kHz
This equation provides a good starting point for picking the inductor value. Most systems can easily tolerate ripple currents in the range of 10% to 50%, so deviating slightly from the calculated value is acceptable for most applications. Pick a standard value inductor close to the
2-PHASE DUAL CONTROLLER
VO1 = 5V/3A VO2 = 3.3V/3A 0 10 20 30 INPUT VOLTAGE (V) 40
3742 F05
Figure 5. RMS Input Current Comparison
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LT3742 applicaTions inForMaTion
value calculated above, and then recheck the amount of ripple current:
IRIPPLE V - VOUT VOUT 1 = IN * * L VIN 500kHz
Inductor, Catch Diode and MOSFET Current Rating Once the inductor and RSENSE values have been chosen, the current ratings of the inductor, catch diode and MOSFET can then be determined. The LT3742 current comparator has a guaranteed maximum threshold of 70mV, and there is a small amount of current overshoot resulting from the response time of the current sense comparator. The components should be rated to handle:
The DC resistance (DCR) of the inductor can have a significant impact on total system efficiency, as it causes an I2RDCR power loss. Consider inductance value, DCR, and current rating when choosing an inductor. Table 1 shows several recommended inductor vendors. Each offers numerous devices in a wide variety of values, current ratings, and package sizes.
Table 1. Recommended Inductor Manufacturers
VENDOR Sumida Toko Wurth NEC-Tokin TDK WEBSITE www.sumida.com www.toko.com www.we-online.com www.nec-tokinamerica.com www.tdk.com
IRATED
70mV VIN + * 100ns RSENSE L
Schottky Catch Diode Selection During output short-circuits, the diode will conduct current most of the time, so it is important to choose a device with a sufficient current rating. In addition, the diode must have a reverse voltage rating greater than the maximum input voltage. Many surface mount Schottky diodes are available in very small packages. Read their data sheets carefully as they typically must be temperature derated. Basically, excessive heating prevents them from being used effectively at their rated maximum current. A few recommended diodes are listed in Table 2.
Table 2. Recommended Schottky Diodes
VENDOR Diodes, Inc. www.diodes.com Microsemi www.microsemi.com On Semiconductor www.onsemi.com DEVICE PDS540 (5A, 40V) SBM1040 (10A, 40V) UPS340 (3A, 40V) UPS840 (8A, 40V) MBRD320 (3A, 20V) MBRD340 (3A, 40V)
Maximum Output Current (RSENSE Value Selection) Maximum output current is determined largely by the values of the current sense resistor, RSENSE (which sets the inductor peak current), and the inductor (which sets the inductor ripple current). The LT3742 current comparator has a guaranteed minimum threshold of 50mV, which does not vary with duty cycle. The maximum output current is calculated:
IOUT(MAX) =
50mV IRIPPLE - RSENSE 2
Rearranging the equation above to solve for RSENSE gives:
Power MOSFET Selection There are several important parameters to consider when choosing an N-channel power MOSFET: drain current (maximum ID); breakdown voltage (maximum VDS and VGS); threshold voltage (VGS(TH)); on-resistance (RDS(ON)); reverse transfer capacitance (CRSS); and total gate charge
RSENSE =
50mV I IOUT(MAX) + RIPPLE 2
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LT3742 applicaTions inForMaTion
(QG). A few simple guidelines will make the selection process easier. The maximum drain current must be higher than the maximum rated current, IRATED, calculated on the previous page. Note that the ID specification is largely temperature dependent (lower ID at higher ambient temperatures), so most data sheets provide a graph or table of ID versus temperature to show this. Ensure that the VDS breakdown voltage is greater than the maximum input voltage and that the VGS breakdown voltage is 8V or greater. The peak-to-peak gate drive for each MOSFET is ~7V, so also ensure that the device chosen will be fully enhanced with a VGS of 7V. This may preclude the use of some MOSFETs with a 20V VGS rating, as some have too high of a threshold voltage. A good rule of thumb is that the maximum threshold voltage should be VGS(TH)(MAX) 3V. 4.5V MOSFETs will work as well. Power losses in the N-channel MOSFET come from two main sources: the on-resistance, RDS(ON), and the reverse transfer capacitance, CRSS. The on-resistance causes ohmic losses (I2RDS(ON)) which typically dominate at input voltages below ~15V. The reverse transfer capacitance results in transition losses which typically dominate for input voltages above ~15V. At higher input voltages, transition losses rapidly increase to the point that the use of a higher RDS(ON) device with lower CRSS will actually
0.7 0.6 MOSFET POWER LOSS (W) 0.5 0.4 0.3 TRANSITION 0.2 0.1 0 0 5 MOSFET POWER LOSS (W) TOTAL = OHMIC + TRANSITION
provide higher efficiency. The power loss in the MOSFET can be approximated by:
PLOSS = (ohmic loss) + ( transition loss) V + VD 2 OUT PLOSS * IOUT RDS(ON) * T VIN + VD
(2 * V
IN
2
* IOUT * CRSS * f
)
where f is the switching frequency (500kHz) and T is a normalizing term to account for the on-resistance change due to temperature. For a maximum ambient temperature of 70C, using T 1.3 is a reasonable choice. The trade-off in RDS(ON) and CRSS can easily be seen in an example using real MOSFET values. To generate a 3.3V, 3A (10W) output, consider two typical N-channel power MOSFETs, both rated at VDS = 30V and both available in the same SO-8 package, but having ~5x differences in on-resistance and reverse transfer capacitance: M1: ID = 11.5A, VGS = 12V, RDS(ON) = 10m, CRSS = 230pF M2: ID = 6.5A, VGS = 20V, RDS(ON) = 50m, CRSS = 45pF Power loss is calculated for both devices over a wide input voltage range (4V VIN 30V), and shown in Figure 6 (as a percentage of the 10W total power). Note that while the low RDS(ON) device power loss is 5x lower at low input
0.7 0.6 0.5 0.4 0.3 0.2 0.1 OHMIC TRANSITION TOTAL = OHMIC + TRANSITION
OHMIC 20 15 10 INPUT VOLTAGE (V) 25 30
3742 F06a
0
0
5
20 15 10 INPUT VOLTAGE (V)
25
30
3742 F06b
Figure 6a. Power Loss Example for M1 (10m, 230pF)
Figure 6b. Power Loss Example for M2 (50m, 45pF)
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LT3742 applicaTions inForMaTion
voltages, it is also 3x higher at high input voltages when compared to the low CRSS device. Total gate charge, QG, is closely related to CRSS. Low gate charge corresponds to a small value of CRSS. Many manufacturers have MOSFETs advertised as "low gate charge" devices (which means they are low CRSS devices) that are specifically designed for low transition loss, and are ideal for high input voltage applications. Input Capacitor Selection For most applications, 10F to 22F of input capacitance per channel will be sufficient. A small 1F bypass capacitor between the VIN and ground pins of the LT3742, placed close to the device, is also suggested for optimal noise immunity. Step-down regulators draw current from the input supply in pulses with very fast rise and fall times. The input capacitor is required to reduce the resulting voltage ripple at the LT3742 and to force this very high frequency switching current into a tight local loop, minimizing EMI. The input capacitor must have low impedance at the switching frequency to do this effectively, and it must have an adequate ripple current rating. With two controllers operating at the same frequency but with different phases and duty cycles, calculating the input capacitor RMS current is not simple. However, a conservative value is the RMS input current for the channel that is delivering the most power (VOUT * IOUT):
IRMS(CIN) = IOUT * VOUT * ( VIN - VOUT ) VIN
The combination of small size and low impedance (low equivalent series resistance, or ESR) of ceramic capacitors make them the preferred choice. The low ESR results in very low input voltage ripple and the capacitors can handle plenty of RMS current. They are also comparatively robust and can be used at their rated voltage. Use only X5R or X7R types because they retain their capacitance over wider voltage and temperature ranges than other ceramics. An alternative to a high value ceramic capacitor is a lower value (1F) along with a larger value (10F to 22F) electrolytic or tantalum capacitor. Because the input capacitor is likely to see high surge currents when the input source is applied, tantalum capacitors should always be surge rated. The manufacturer may also recommend operation below the rated voltage of the capacitor. Be sure to place the 1F ceramic as close as possible to the N-channel power MOSFET. Output Capacitor Selection A good starting value for output capacitance is to provide 10F of COUT for every 1A of output current. For lower output voltages (under 3.3V) and for applications needing the best possible transient performance, the ratio should be 20F to 30F of COUT for every 1A of output current. X5R and X7R ceramics are an excellent choice for the output capacitance. Aluminum electrolytics can be used, but typically the ESR is too large to deliver low output voltage ripple. Tantalum and newer, lower ESR organic electrolytic capacitors are also possible choices, and the manufactures will specify the ESR. Because the volume of the capacitor determines the ESR, both the size and value will be larger than a ceramic capacitor that would give you similar output ripple voltage performance. The output capacitor filters the inductor ripple current to generate an output with low ripple. It also stores energy in order to satisfy transient loads and to stabilize the
IRMS(CIN) is largest (IOUT/2) when VIN = 2VOUT (at DC = 50%). As the second, lower power channel draws input current, the input capacitor's RMS current actually decreases as the out-of-phase current cancels the current drawn by the higher power channel, so choosing an input capacitor with an RMS ripple current rating of IOUT,MAX/2 is sufficient.
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LT3742 applicaTions inForMaTion
LT3742's control loop. Output ripple can be estimated with the following equation: The output voltage for each controller is programmed with a resistor divider between the output and the FB pin. Always use 1% resistors (or better) for the best output voltage accuracy. The value of RA should be 8k or less, and the value of R1 should be chosen according to:
1 VRIPPLE = IL + ESR 8 * fSW * COUT
where IL is the inductor ripple current and fSW is the switching frequency (500kHz). The ESR is so low for ceramic capacitors that it can be left out of the above calculation. The output voltage ripple will be highest at maximum input voltage (IL increases with input voltage). Table 3 shows several low-ESR capacitor manufacturers.
Table 3. Low ESR Surface Mount Capacitors
VENDOR Taiyo Yuden www.t-yuden.com Murata www.murata.com Kemet www.kemet.com Sanyo www.sanyo.com Panasonic www.panasonic.com TDK www.tdk.com Nippon Chemicon www.chemi-con.co.jp TYPE Ceramic X5R, X7R Ceramic X5R, X7R Tantalum Ta Organic Al Organic Ta or Al Organic Al Organic Ceramic X5R, X7R Ceramic X5R, X7R T491, T494, T495 T520 A700 POSCAP SP CAP SERIES
V RB = RA * OUT - 1 0.8V
Output Short-Circuit Protection Because the LT3742 constantly monitors the inductor current, both devices inherently providing excellent output short-circuit protection. The N-channel MOSFET is not allowed to turn on unless the inductor current is below the threshold of the current sense comparator. This guarantees that the inductor current will not "run away" and the controller will skip cycles until the inductor current has dropped below the current sense threshold. Loop Compensation An external resistor and capacitor connected in series from the VC pin to ground provides loop compensation for each controller. Sometimes a second, smaller valued capacitor is placed in parallel to filter switching frequency noise from the VC pin. Loop compensation determines the stability and transient performance of each controller. A practical approach is to start with values of RC = 10k , and CC = 330pF then tune the compensation network to optimize the performance. When adjusting these values, change only one value at a time (RC or CC), then see how the transient response is affected. The simplest way to check loop stability is to apply a load current step while observing the transient response at the output. Stability should then be checked across all operating conditions, including load current, input voltage, and temperature to ensure a robust design.
VOUT2
Setting Output Voltage The output of a bipolar controller requires a minimum load to prevent current sourced from the switch pin charging the output capacitor above the desired output voltage. This current, approximately 5mA, may be accounted for in the feedback string or the user may choose to force a minimum load in their application.
VOUT1 R1B R1A
3742 F07
LT3742 VFB1 VFB2
R2B R2A
Figure 7. Setting Output Voltage with the FB Pin
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LT3742 applicaTions inForMaTion
Bias Supply Considerations The LT3742 uses an internal boost regulator to provide a bias rail for enhancement of the external MOSFETs. This bias rail is regulated to VIN + 7V and must be in regulation before either controller is allowed to start switching. As this is a high speed switching regulator, standard procedures must be followed regarding placement of the external components. The SWB node should be kept small to reduce EMI effects and the bias decoupling capacitor (CBIAS) should be kept close to the BIAS pin and VIN. A slight surplus of power is available from this supply and it can be tapped after stringent engineering evaluation. PC Board Layout Considerations As with all switching regulators, careful attention must be paid to the PCB board layout and component placement. * Place the power components close together with short and wide interconnecting traces. The power components consist of the top MOSFETs, catch diodes and the inductors CIN and COUT. One way to approach this is to simply place them on the board first. * Similar attention should be paid to the power components that make up the boost converter. They should also be placed close together with short and wide traces. * Always use a ground plane under the switching regulator to minimize interplane coupling. * Minimize the parasitic inductance in the loop of CIN, MOSFET and catch diode, which carry large switching currents. * Use compact plane for switch node (SW) to improve cooling of the MOSFETs and to keep EMI low. * Use planes for VIN and VOUT to maintain good voltage filtering and to keep power losses low. Unused areas can be filled with copper and connect to any DC node (VIN, VOUT, GND). * Place CB close to BIAS pin and input capacitor. * Keep the high dv/dt nodes (SW1, SW2, G1, G2, CIN1, CIN2, SWB) away from sensitive small-signal nodes. Demo board gerber files are available to assist with a reliable layout. It will be difficult to achieve data sheet performance specifications with improper layout.
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LT3742 applicaTions inForMaTion
VIN VOUT1
VIN SHDN
RUN1
SYSTEM GROUND
SHDN
RUN2
VIN
VOUT2
3742 F08
VIAS TO LOCAL GROUND PLANE OUTLINE OF LOCAL GROUND PLANE
Figure 8. A Good PCB Layout Ensures Proper, Low EMI Operation
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LT3742 Typical applicaTions
Supercap Charger Plus a DC/DC Buck Converter
L3 22H R7 357k R8 124k LT3742 VIN C1 6.8F M1 1 24 21 20 19 R2 200 D1 17 16 RUN1 M3 C7 1nF CC1 680pF 18 RC1 51k 14 15 13 C8 1nF CC2 1000pF
3742 TA02
VIN 5.5V TO 30V C5 1F
C6 4.7F 5 4 SWB BIAS
2 3 VIN UVLO
VOUT1 5V 4A C2 150F
RS1 0.010
L1 4.7H
G1 SW1 SENSE1+ SENSE1- FB1
G2 SW2 SENSE2+ SENSE2- FB2
6 7 10 11 12
M2
L2 47H
RS2 0.030
C3 6.8F
VIN SUPERCAP CHARGER OUTPUT
R1 1.05k
C4 47F D2
150mF
PG1
PG1 RUN/SS1 VC1 GND 25
PG2 RUN/SS2 VC2
PG2
M4
RUN2
D1, D2: DIODES INC. PDS1040 M1, M2: SILICONIX Si7884DP
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20
LT3742 Typical applicaTions
8V and 5V Dual Step-Down Converter
L3 22H R1 45.3k R1 20k LT3742 VIN C1 10F M1 1 24 21 20 19 R2 200 D1 17 16 RUN1 M3 C7 1nF CC1 1000pF 18 RC1 30k 14 15 13 RC2 20k C8 1nF CC2 1000pF
3742 TA03
VIN 14V C5 1F
C6 2.2F 5 4 SWB BIAS
2 3 VIN UVLO
VOUT1 8V 4A C2 47F
RS1 0.01
L1 6.5H
G1 SW1 SENSE1+ SENSE1- FB1
G2 SW2 SENSE2+ SENSE2- FB2
6 7 10 11 12
M2
L2 6.5H
RS2 0.01
C3 10F
VIN
R1 1.8k
R3 1.05k R4 200
VOUT2 5V 4A C4 47F
D2
PG1
PG1 RUN/SS1 VC1 GND 25
PG2 RUN/SS2 VC2
PG2
M4
RUN2
C2, C4: MURATA GRM32ER71A476K D1, D2: DIODES INC. PDS1040 L1, L2: WURTH ELEKTRONIK 744314650 M1, M2: FAIRCHILD FDS4470
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LT3742 Typical applicaTions
5V and 3.3V Dual Step-Down Converter
L3 22H 348k 1F 130k LT3742 VIN 10F VOUT1 3.3V 4A 220F 200 PG1 1nF 680pF 51k PG1 RUN/SS1 VC1 PG2 RUN/SS2 VC2 GND PG2 51k 1nF 680pF 10m 619 L1 3.3H G1 SW1 SENSE1+ SENSE1- FB1 G2 SW2 SENSE2+ SENSE2- FB2 D2 L2 4.7H 10m 1.05k 200 VIN 10F VOUT2 5V 4A 150F
VIN 14V
2.2F SWB BIAS
VIN UVLO
68pF
D1, D2: DIODES INC. PDS1040 L1: VISHAY IHLP2525CZER3R3 L2: VISHAY IHLP2525CZER4R7 L3: COILCRAFT: ME3220-223KL M1, M2: VISHAY Si7848DP-T1-E3
3742 TA04a
Efficiency vs Load Current
90 5VOUT 80 EFFICIENCY (%) 3.3VOUT 70
60
50
0
1
2 LOAD CURRENT (A)
3
4
3742 TA04b
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22
LT3742 Typical applicaTions
High Current, Low Ripple 12V Step-Down Converter
VIN 24V C5 1F
L3 10H R7 124k R8 20.0k LT3742
C6 4.7F
VIN UVLO
SWB BIAS
VIN
C1 10F RS1 0.010
M1
G1
G2
M2
VIN C3 10F RS2 0.010
VOUT1 12V 8A
L1 8.2H SW1 SENSE1+ SENSE1- D1 SW2 SENSE2+ SENSE2- FB2
L2 8.2H
R1 2.8k R2 200 C7 1nF CC1 680pF
D2 PG1 PG1 FB1 RUN/SS1 VC1 PG2 RUN/SS2 VC2 GND PG2
RC1 51k
COUTA-COUTD: KEMET T495E107K020E060 D1, D2: DIODES INC. PDS1040 L1, L2: NEC/TOKIN PLC12458R2 M1, M2: ROHM RSS065N03
COUTA 100F 20V
COUTB 100F 20V
COUTC 100F 20V
COUTD 100F 20V
3742 TA05a
12VOUT Efficiency vs Load Current
100
90 EFFICIENCY (%)
85
70
60
0
1
2
5 6 3 4 LOAD CURRENT (A)
7
8
3742 TA05b
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LT3742 package DescripTion
UF Package 24-Lead Plastic QFN (4mm x 4mm)
(Reference LTC DWG # 05-08-1697)
0.70 0.05
4.50 0.05 2.45 0.05 3.10 0.05 (4 SIDES)
PACKAGE OUTLINE 0.25 0.05 0.50 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 0.75 0.05 BOTTOM VIEW--EXPOSED PAD R = 0.115 TYP PIN 1 NOTCH R = 0.20 TYP OR 0.35 x 45 CHAMFER
4.00 0.10 (4 SIDES) PIN 1 TOP MARK (NOTE 6)
23 24 0.40 0.10 1 2
2.45 0.10 (4-SIDES)
(UF24) QFN 0105
0.200 REF 0.00 - 0.05 NOTE: 1. DRAWING PROPOSED TO BE MADE A JEDEC PACKAGE OUTLINE MO-220 VARIATION (WGGD-X)--TO BE APPROVED 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE, IF PRESENT 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE
0.25 0.05 0.50 BSC
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LT3742 revision hisTory
REV A DATE 5/11 DESCRIPTION Revised Conditions in the Electrical Characteristics section. Revised the title of curve G04 in the Typical Performance Characteristics section. Updated the PG1, PG2 pin description in the Pin Functions section. Updated values in the Block Diagram, Operation, and Applications Information sections. PAGE NUMBER 2, 3 4 6 7-12
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Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
25
LT3742 relaTeD parTs
PART NUMBER LTC1625/LTC1775 LTC1735 LTC1778 LT3430/LT3431 LT3724 LT3800 LT3844 LTC3727A-1 LTC3728 LTC3729 LTC3731 LTC3773 DESCRIPTION No RSENSETM Current Mode Synchronous Step-Down Controllers High Efficiency Synchronous Step-Down Switching Regulator No RSENSE Wide Input Range Synchronous Step-Down Controller Monolithic 3A, 200kHz/500kHz Step-Down Regulators High Voltage Current Mode Switching Regulator Controllers High Voltage Synchronous Controller High Voltage Current Mode Controller with Programmable Operating Frequency Dual, 2-Phase Synchronous Controller 2-Phase 550kHz, Dual Synchronous Step-Down Controller 20A to 200A PolyPhase(R) Synchronous Controllers 3-Phase, 600kHz Synchronous Step-Down Controller Triple Output DC/DC Synchronous Controller COMMENTS 97% Efficiency, No Sense Resistor, 16-Pin SSOP Output Fault Protection, 16-Pin SSOP Up to 97% Efficiency, 4V VIN 36V, 0.8V VOUT (0.9)(VIN), IOUT Up to 20A 5.5V = LTC3703/LTC3703-5 100V Synchronous Switching Regulator Controllers
LTC3826/LTC3826-1 30A IQ, Dual, 2-Phase Synchronous Step-Down Controllers 2-Phase Operation, 30A One Channel No Load IQ (50A Total), 4V VIN 36V, 0.8V VOUT 10V LTC3827/LTC3827-1 Low IQ Dual Synchronous Controllers LTC3834/LTC3834-1 Low IQ Synchronous Step-Down Controllers LTC3835/LTC3835-1 Low IQ Synchronous Step-Down Controllers LTC3850 LT3845 Dual, 2-Phase Synchronous Step-Down DC/DC Controller High Voltage Synchronous Step-Down Single Output Controller 2-Phase Operation, 115A Total No Load IQ, 4V VIN 36V, 80A No Load IQ with One Channel On 30A No Load IQ, 4V VIN 36V, 0.8V VOUT 10V 80A No Load IQ, 4V VIN 36V, 0.8V VOUT 10V 2-Phase Operation, 4V VIN 24V, 95% Efficiency, No RSENSE Option, IOUT Up to 20A, 4mm 4mm QFN Very Low Quiescent Current (120A), VIN Up to 60V, Fixed Frequency 100kHz to 500kHz, Synchronizable Up to 600kHz
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26 Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 l FAX: (408) 434-0507
l
LT 0511 REV A * PRINTED IN USA
www.linear.com
LINEAR TECHNOLOGY CORPORATION 2007

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