View LTC3704_224014.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

Final Electrical Specifications
LTC3704 Wide Input Range, No RSENSETM Positive-to-Negative DC/DC Controller
FEATURES
s s s
DESCRIPTIO
December 2001
s s s s s
s s s s
s
High Efficiency Operation (No Sense Resistor Required) Wide Input Voltage Range: 2.5V to 36V Current Mode Control Provides Excellent Transient Response High Maximum Duty Cycle (Typ 92%) 2% RUN Pin Threshold with 100mV Hysteresis 1% Internal Voltage Reference Micropower Shutdown: IQ = 10A Programmable Operating Frequency (50kHz to 1MHz) with One External Resistor Synchronizable to an External Clock Up to 1.3 x fOSC User-Controlled Pulse Skip or Burst Mode(R) Operation Internal 5.2V Low Dropout Voltage Regulator Capable of Operating with a Sense Resistor for High Output Voltage Applications Small 10-Lead MSOP Package
The LTC(R)3704 is a wide input range, current mode, positive-to-negative DC/DC controller that drives an N-channel power MOSFET and requires very few external components. Intended for low to high power applications, it eliminates the need for a current sense resistor by utilizing the power MOSFET's on-resistance, thereby maximizing efficiency. The IC's operating frequency can be set with an external resistor over a 50kHz to 1MHz range, and can be synchronized to an external clock using the MODE/SYNC pin. Burst Mode operation at light loads, a low minimum operating supply voltage of 2.5V and a low shutdown quiescent current of 10A make the LTC3704 ideally suited for battery-operated systems. For applications requiring constant frequency operation, the Burst Mode operation feature can be defeated using the MODE/SYNC pin. Higher than 36V switch voltage applications are possible with the LTC3704 by connecting the SENSE pin to a resistor in the source of the power MOSFET. The LTC3704 is available in the 10-lead MSOP package.
, LTC and LT are registered trademarks of Linear Technology Corporation. Burst Mode is a registered trademark of Linear Technology Corporation. RSENSE is a trademark of Linear Technology Corporation.
APPLICATIO S
s s s s
Telecom Power Supplies Portable Electronic Equipment Cable and DSL Modems Router Supplies
TYPICAL APPLICATIO
R1 1M 1 2 RUN ITH LTC3704 RC 3k 3 4 5 CC1 4.7nF RT 80.6k 1% RFB1 1.21k 1% RFB2 3.65k 1% NFB FREQ MODE/SYNC
*
L1* 10 SENSE VIN 9 CDC 47F
VIN 5V to 15V VOUT -5.0V 3A to 5A L2*
*
EFFICIENCY (%)
8 GATE GND 7 6 D1 CVCC 4.7F CIN 47F M1
INTVCC
COUT 100F (X2)
GND
3704 TA01
CIN, CDC : TDK C5750X5R1C476M COUT: TDK C5750X5R0J107M CVCC: TAIYO YUDEN LMK316BJ475ML
D1: MBRD835L (ON SEMICONDUCTOR) L1, L2: BH ELECTRONICS BH510-1009 M1: Si4884 (SILICONIX/VISHAY)
Figure 1. High Efficiency Positive to Negative Supply
3704i
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.
U
100 90 80 70 60 VIN = 10V 50 40 30 20 0.001 VIN = 5V VIN = 15V
U
U
High Efficiency
0.01 1.0 0.1 OUTPUT CURRENT (A)
10
3704 TA01b
1
LTC3704
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
ORDER PART NUMBER
TOP VIEW RUN ITH NFB FREQ MODE/ SYNC 1 2 3 4 5 10 9 8 7 6 SENSE VIN INTVCC GATE GND
VIN Voltage ............................................... - 0.3V to 36V INTVCC Voltage ........................................... - 0.3V to 7V INTVCC Output Current ........................................ 50mA GATE Voltage ........................... - 0.3V to VINTVCC + 0.3V ITH Voltage ............................................... - 0.3V to 2.7V NFB Voltage .............................................. -2.7V to 2.7V RUN, MODE/SYNC Voltages ....................... - 0.3V to 7V FREQ Voltage ............................................- 0.3V to 1.5V SENSE Pin Voltage ................................... - 0.3V to 36V Operating Temperature Range (Note 2) .. - 40C to 85C Junction Temperature (Note 3) ............................ 125C Storage Temperature Range ................. - 65C to 150C Lead Temperature (Soldering, 10 sec).................. 300C
LTC3704EMS
MS PACKAGE 10-LEAD PLASTIC MSOP
MS PART MARKING LTYT
TJMAX = 125C, JA = 120C/ W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The q denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = VINTVCC = 5V, VRUN = 1.5V, RT = 80k, VMODE/SYNC = 0V, unless otherwise specified.
SYMBOL VIN(MIN) IQ PARAMETER Minimum Input Voltage Input Voltage Supply Current Continuous Mode Burst Mode Operation, No Load Shutdown Mode Rising RUN Input Threshold Voltage Falling RUN Input Threshold Voltage
q
CONDITIONS
MIN 2.5
TYP
MAX
UNITS V
Main Control Loop (Note 4) VMODE/SYNC = 5V, VITH = 0.75V VMODE/SYNC = 0V, VITH = 0.2V (Note 5) VRUN = 0V 1.223 1.198 50 VITH = 0.2V (Note 5)
q
550 250 10 1.348 1.248 100 1 -1.218 -1.212 -1.230 7.5 0.002
q
1000 500 20 1.273 1.298 150 100 -1.242 -1.248 15 0.02
VRUN+ VRUN- VRUN(HYST) IRUN VNFB INFB VNFB VIN VNFB VITH gm VITH(BURST) ISENSE(ON) ISENSE(OFF)
RUN Pin Input Threshold Hysteresis RUN Input Current Negative Feedback Voltage NFB Pin Input Current Line Regulation Load Regulation Error Amplifier Transconductance Burst Mode Operation ITH Pin Voltage SENSE Pin Current (GATE High) SENSE Pin Current (GATE Low)
VITH = 0.2V (Note 5) 2.5V VIN 30V VMODE/SYNC = 0V, VTH = 0.5V to 0.90V (Note 5) ITH Pin Load = 5A (Note 5) Falling ITH Voltage (Note 5) Duty Cycle < 20% VSENSE = 0V VSENSE = 30V 120 -1
- 0.1 650 0.3 150 40 0.1 180 75 5
VSENSE(MAX) Maximum Current Sense Input Threshold
2
U
A A A V V V mV nA V V A %/V % mho V mV A A
3704i
W
U
U
WW
W
LTC3704
The q denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = VINTVCC = 5V, VRUN = 1.5V, RFREQ = 80k, VMODE/SYNC = 0V, unless otherwise specified.
SYMBOL Oscillator fOSC DMAX fSYNC/fOSC tSYNC(MIN) tSYNC(MAX) VIL(MODE) VIH(MODE) RMODE/SYNC VFREQ VINTVCC VINTVCC VIN1 VINTVCC VIN2 VLDO(LOAD) VDROPOUT IINTVCC GATE Driver tr tf GATE Driver Output Rise Time GATE Driver Output Fall Time CL = 3300pF (Note 7) CL = 3300pF (Note 7) 17 8 100 100 ns ns Oscillator Frequency Oscillator Frequency Range Maximum Duty Cycle Recommended Maximum Synchronized Frequency Ratio MODE/SYNC Minimum Input Pulse Width MODE/SYNC Maximum Input Pulse Width Low Level MODE/SYNC Input Voltage High Level MODE/SYNC Input Voltage MODE/SYNC Input Pull-Down Resistance Nominal FREQ Pin Voltage INTVCC Regulator Output Voltage INTVCC Regulator Line Regulation INTVCC Regulator Line Regulation INTVCC Load Regulation INTVCC Regulator Dropout Voltage Bootstrap Mode INTVCC Supply Current in Shutdown VIN = 7.5V 7.5V VIN 15V 15V VIN 30V 0 IINTVCC 20mA VIN = 5V, INTVCC Load = 20mA RUN = 0V, SENSE = 5V -2 5.0 1.2 50 0.62 5.2 8 70 - 0.2 280 10 20 5.4 25 200 fOSC = 300kHz (Note 6) VSYNC = 0V to 5V VSYNC = 0V to 5V RFREQ = 80k 250 50 87 92 1.25 25 0.8/fOSC 0.3 300 350 1000 97 1.30 ns ns V V k V V mV mV % mV A kHz kHz % PARAMETER CONDITIONS MIN TYP MAX UNITS
ELECTRICAL CHARACTERISTICS
Low Dropout Regulator
Note 1: Absolute Maximum Ratings are those values beyond which the life of the device may be impaired. Note 2: The LTC3704E is guaranteed to meet performance specifications from 0C to 70C. Specifications over the - 40C to 85C operating temperature range are assured by design, characterization and correlation with statistical process controls. Note 3: TJ is calculated from the ambient temperature TA and power dissipation PD according to the following formula: TJ = TA + (PD * 120C/W) Note 4: The dynamic input supply current is higher due to power MOSFET gate charging (QG * fOSC). See Applications Information.
Note 5: The LTC3704 is tested in a feedback loop that servos VNFB to the reference voltage with the ITH pin forced to a voltage between 0V and 1.4V (the no load to full load operating voltage range for the ITH pin is 0.3V to 1.23V). Note 6: In a synchronized application, the internal slope compensation gain is increased by 25%. Synchronizing to a significantly higher ratio will reduce the effective amount of slope compensation, which could result in subharmonic oscillation for duty cycles greater than 50%. Note 7: Rise and fall times are measured at 10% and 90% levels.
3704i
3
LTC3704
PI FU CTIO S
RUN (Pin 1): The RUN pin provides the user with an accurate means for sensing the input voltage and programming the start-up threshold for the converter. The falling RUN pin threshold is nominally 1.248V and the comparator has 100mV of hysteresis for noise immunity. When the RUN pin is below this input threshold, the IC is shut down and the VIN supply current is kept to a low value (typ 10A). The Absolute Maximum Rating for the voltage on this pin is 7V. ITH (Pin 2): Error Amplifier Compensation Pin. The current comparator input threshold increases with this control voltage. Nominal voltage range for this pin is 0V to 1.40V. NFB (Pin 3): Receives the feedback voltage from the external resistor divider across the output. Nominal voltage for this pin in regulaton is -1.230V. FREQ (Pin 4): A resistor from the FREQ pin to ground programs the operating frequency of the chip. The nominal voltage at the FREQ pin is 0.62V. MODE/SYNC (Pin 5): This input controls the operating mode of the converter and allows for synchronizing the operating frequency to an external clock. If the MODE/ SYNC pin is connected to ground, Burst Mode operation is enabled. If the MODE/SYNC pin is connected to INTVCC, or if an external logic-level synchronization signal is applied to this input, Burst Mode operation is disabled and the IC operates in a continuous mode. GND (Pin 6): Ground Pin. GATE (Pin 7): Gate Driver Output. INTVCC (Pin 8): The Internal 5.20V Regulator Output. The gate driver and control circuits are powered from this voltage. Decouple this pin locally to the IC ground with a minimum of 4.7F low ESR tantalum or ceramic capacitor. VIN (Pin 9): Main Supply Pin. Must be closely decoupled to ground. SENSE (Pin 10): The Current Sense Input for the Control Loop. Connect this pin to the drain of the power MOSFET for VDS sensing and highest efficiency. Alternatively, the SENSE pin may be connected to a resistor in the source of the power MOSFET. Internal leading edge blanking is provided for both sensing methods.
4
U
U
U
3704i
LTC3704
BLOCK DIAGRA
FREQ 4 0.62V MODE/SYNC 5 NFB 3 200k 200k 50k S Q R BUFFER PWM LATCH IOSC V-TO-I OSC
0.30V EA gm 1.230V ITH 2 INTVCC 8 5.2V
LDO
1.230V SLOPE 1.230V
UV TO START-UP CONTROL GND BIAS VREF 6
3704 BD
2.00V
+
-
+
+
+
-
-
-
W
RUN SLOPE COMPENSATION BIAS AND START-UP CONTROL
+
C2
1
-
100mV HYSTERESIS (1.348V RISING)
1.248V VIN 9
INTVCC GATE LOGIC GND 7
SENSE
+
C1
10
-
CURRENT COMPARATOR
BURST COMPARATOR
V-TO-I ILOOP RLOOP
VIN
3704i
5
LTC3704
OPERATIO
Main Control Loop The LTC3704 is a constant frequency, current mode controller for DC/DC positive-to-negative converter applications. The LTC3704 is distinguished from conventional current mode controllers because the current control loop can be closed by sensing the voltage drop across the power MOSFET switch instead of across a discrete sense resistor, as shown in Figure 2. This sensing technique improves efficiency, increases power density, and reduces the cost of the overall solution.
VIN VIN SENSE GATE GND GND VSW
2a. SENSE Pin Connection for Maximum Efficiency (VSW < 36V)
VIN VIN GATE SENSE GND GND VSW
2b. SENSE Pin Connection for Precise Control of Peak IIN/IOUT or for VSW > 36V
Figure 2. Using the SENSE Pin On the LTC3704
For circuit operation, please refer to the Block Diagram of the IC and Figure 1. In normal operation, the power MOSFET is turned on when the oscillator sets the PWM latch and is turned off when the current comparator C1 resets the latch. The divided-down output voltage is compared to an internal 1.230V reference by the error amplifier EA, which outputs an error signal at the ITH pin. The voltage on the ITH pin sets the current comparator C1 input threshold. When the load current increases, a fall in the NFB voltage relative to the reference voltage causes the ITH pin to rise, which causes the current comparator C1 to trip at a higher peak inductor current value. The average inductor current will therefore rise until it equals the load current, thereby maintaining output regulation.
6
U
The nominal operating frequency of the LTC3704 is programmed using a resistor from the FREQ pin to ground and can be controlled over a 50kHz to 1000kHz range. In addition, the internal oscillator can be synchronized to an external clock applied to the MODE/SYNC pin and can be locked to a frequency between 100% and 130% of its nominal value. When the MODE/SYNC pin is left open, it is pulled low by an internal 50k resistor and Burst Mode operation is enabled. If this pin is taken above 2V or an external clock is applied, Burst Mode operation is disabled and the IC operates in continuous mode. With no load (or an extremely light load), the controller will skip pulses in order to maintain regulation and prevent excessive output ripple. The RUN pin controls whether the IC is enabled or is in a low current shutdown state. A micropower 1.248V reference and comparator C2 allow the user to program the supply voltage at which the IC turns on and off (comparator C2 has 100mV of hysteresis for noise immunity). With the RUN pin below 1.248V, the chip is off and the input supply current is typically only 10A. The LTC3704 can be used either by sensing the voltage drop across the power MOSFET or by connecting the SENSE pin to a conventional shunt resistor in the source of the power MOSFET, as shown in Figure 2. Sensing the voltage across the power MOSFET maximizes converter efficiency and minimizes the component count, but limits the output voltage to the maximum rating for this pin (36V). By connecting the SENSE pin to a resistor in the source of the power MOSFET, the user is able to program output voltages significantly greater than the 36V maximum input voltage rating for the IC. Programming the Operating Mode For applications where maximizing the efficiency at very light loads (e.g., <100A) is a high priority, Burst Mode operation should be applied (i.e., the MODE/SYNC pin should be connected to ground). In applications where fixed frequency operation is more critical than low current efficiency, or where the lowest output ripple is desired, pulse-skip mode operation should be used and the MODE/SYNC pin should be connected to the INTVCC pin. This allows discontinuous conduction mode (DCM) operation down to near the limit defined by the chip's
3704i
RS
3704 F02
LTC3704
OPERATIO
minimum on-time (about 175ns). Below this output current level, the converter will begin to skip cycles in order to maintain output regulation. Figures 3 and 4 show the light load switching waveforms for Burst Mode and Pulse-Skip Mode operation for the converter in Figure 1. Burst Mode Operation Burst Mode operation is selected by leaving the MODE/ SYNC pin unconnected or by connecting it to ground. In normal operation, the range on the ITH pin corresponding to no load to full load is 0.30V to 1.2V. In Burst Mode operation, if the error amplifier EA drives the ITH voltage below 0.525V, the buffered ITH input to the current comparator C1 will be clamped at 0.525V (which corresponds to 25% of maximum load current). The inductor current peak is then held at approximately 30mV divided by the power MOSFET RDS(ON). If the ITH pin drops below 0.30V, the Burst Mode comparator B1 will turn off the power MOSFET and scale back the quiescent current of the IC to 250A (sleep mode). In this condition, the load current will be supplied by the output capacitor until the ITH voltage rises above the 50mV hysteresis of the burst comparator. At light loads, short bursts of switching (where the average inductor current is 25% of its maximum value) followed by long periods of sleep will be observed, thereby greatly improving converter efficiency. Oscilloscope waveforms illustrating Burst Mode operation are shown in Figure 3.
MODE/SYNC = 0V (Burst Mode OPERATION) VOUT 50mV/DIV
IL 5A/DIV
Figure 3. LTC3704 Burst Mode Operation (MODE/SYNC = 0V) at Low Output Current
Pulse-Skip Mode Operation With the MODE/SYNC pin tied to a DC voltage above 2V, Burst Mode operation is disabled. The internal, 0.525V
U
buffered ITH burst clamp is removed, allowing the ITH pin to directly control the current comparator from no load to full load. With no load, the ITH pin is driven below 0.30V, the power MOSFET is turned off and sleep mode is invoked. Oscilloscope waveforms illustrating this mode of operation are shown in Figure 4.
MODE/SYNC = INTVCC (PULSE-SKIP MODE) VOUT 50mV/DIV IL 5A/DIV 2s/DIV
3704 F04
Figure 4. LTC3704 Low Output Current Operation with Burst Mode Operation Disabled (MODE/SYNC = INTVCC)
When an external clock signal drives the MODE/SYNC pin at a rate faster than the chip's internal oscillator, the oscillator will synchronize to it. In this synchronized mode, Burst Mode operation is disabled. The constant frequency associated with synchronized operation provides a more controlled noise spectrum from the converter, at the expense of overall system efficiency of light loads. When the oscillator's internal logic circuitry detects a synchronizing signal on the MODE/SYNC pin, the internal oscillator ramp is terminated early and the slope compensation is increased by approximately 30%. As a result, in applications requiring synchronization, it is recommended that the nominal operating frequency of the IC be programmed to be about 75% of the external clock frequency. Attempting to synchronize to too high an external frequency (above 1.3fO) can result in inadequate slope compensation and possible subharmonic oscillation (or jitter). The external clock signal must exceed 2V for at least 25ns, and should have a maximum duty cycle of 80%, as shown in Figure 5. The MOSFET turn on will synchronize to the rising edge of the external clock signal.
10s/DIV
3704 F03
3704i
7
LTC3704
APPLICATIO S I FOR ATIO
MODE/ SYNC tMIN = 25ns 0.8T T T = 1/fO
2V TO 7V
GATE
D = 40%
ISW
1.230V
Programming the Operating Frequency The choice of operating frequency and inductor value is a tradeoff between efficiency and component size. Low frequency operation improves efficiency by reducing MOSFET and diode switching losses. However, lower frequency operation requires more inductance for a given amount of load current. The LTC3704 uses a constant frequency architecture that can be programmed over a 50kHz to 1000kHz range with a single external resistor from the FREQ pin to ground, as shown in Figure 1. The nominal voltage on the FREQ pin is 0.6V, and the current that flows into the FREQ pin is used to charge and discharge an internal oscillator capacitor. A graph for selecting the value of RT for a given operating frequency is shown in Figure 6.
1000
R2
Figure 7. Bypassing the LDO Regulator and Gate Driver Supply
100
For input voltages that don't exceed 7V (the absolute maximum rating for this pin), the internal low dropout regulator in the LTC3704 is redundant and the INTVCC pin can be shorted directly to the VIN pin. With the INTVCC pin shorted to VIN, however, the divider that programs the regulated INTVCC voltage will draw 10A of current from the input supply, even in shutdown mode. For applications that require the lowest shutdown mode input supply current, do not connect the INTVCC pin to VIN. Regardless of whether the INTVCC pin is shorted to VIN or not, it is always necessary to have the driver circuitry bypassed with a 4.7F tantalum or low ESR ceramic capacitor to ground immediately adjacent to the INTVCC and GND pins. In an actual application, most of the IC supply current is used to drive the gate capacitance of the power MOSFET. As a result, high input voltage applications in which a large power MOSFET is being driven at high frequencies can
3704i
RT (k)
10
0 100 200 300 400 500 600 700 800 900 1000 FREQUENCY (kHz)
3704 F06
Figure 6. Timing Resistor (RT) Value
8
+
Figure 5. MODE/SYNC Clock Input and Switching Waveforms for Synchronized Operation
-
3404 F05
U
INTVCC Regulator Bypassing and Operation An internal, P-channel low dropout voltage regulator produces the 5.2V supply which powers the gate driver and logic circuitry within the LTC3704, as shown in Figure 7. The INTVCC regulator can supply up to 50mA and must be bypassed to ground immediately adjacent to the IC pins with a minimum of 4.7F tantalum or ceramic capacitor. Good bypassing is necessary to supply the high transient currents required by the MOSFET gate driver.
VIN INPUT SUPPLY 2.5V TO 30V P-CH CIN R1 5.2V INTVCC
W
UU
+
LOGIC DRIVER GATE
CVCC 4.7F M1
GND PLACE AS CLOSE AS POSSIBLE TO DEVICE PINS
GND
3704 F07
LTC3704
APPLICATIO S I FOR ATIO
cause the LTC3704 to exceed its maximum junction temperature rating. The junction temperature can be estimated using the following equations: IQ(TOT) IQ + f * QG PIC = VIN * (IQ + f * QG) TJ = TA + PIC * RTH(JA) The total quiescent current IQ(TOT) consists of the static supply current (IQ) and the current required to charge and discharge the gate of the power MOSFET. The 10-pin MSOP package has a thermal resistance of RTH(JA) = 120C/W. As an example, consider a power supply with VIN = 5V and VSW(MAX) = 12V. The switching frequency is 500kHz, and the maximum ambient temperature is 70C. The power MOSFET chosen is the IRF7805, which has a maximum RDS(ON) of 11m (at room temperature) and a maximum total gate charge of 37nC (the temperature coefficient of the gate charge is low). IQ(TOT) = 600A + 37nC * 500kHz = 19.1mA PIC = 5V * 19.1mA = 95mW TJ = 70C + 120C/W * 95mW = 81.4C This demonstrates how significant the gate charge current can be when compared to the static quiescent current in the IC. To prevent the maximum junction temperature from being exceeded, the input supply current must be checked when operating in a continuous mode at high VIN. A tradeoff between the operating frequency and the size of the power MOSFET may need to be made in order to maintain a reliable IC junction temperature. Prior to lowering the operating frequency, however, be sure to check with power MOSFET manufacturers for their latest-and-greatest low QG, low RDS(ON) devices. Power MOSFET manufacturing technologies are continually improving, with newer and better performance devices being introduced almost yearly.
U
Output Voltage Programming The output voltage is set by a resistor divider according to the following formula:
W
UU
R2 VO = VREF * 1 + + INFB * R2 R1
where VREF = -1.230V, and INFB is the current which flows out of the NFB pin (INFB = -7.5A). In order to properly dimension R2, including the effect of the NFB pin current, the following formula can be used:
R2 = VOUT - VREF VREF + INFB R1
The nominal 7.5A current which flows out of the NFB pin has a production tolerance of approximately 2.5A, so an output divider current of 500A (R1 = 2.49k) results in a 0.5% uncertainty in the output voltage. For low power applications where the output voltage tolerance is less important, efficiency can be increased by increasing the value of R1. Programming Turn-On and Turn-Off Thresholds with the RUN Pin The LTC3704 contains an independent, micropower voltage reference and comparator detection circuit that remains active even when the device is shut down, as shown in Figure 8. This allows users to accurately program an input voltage at which the converter will turn on and off. The falling threshold voltage on the RUN pin is equal to the internal reference voltage of 1.248V. The comparator has 100mV of hysteresis to increase noise immunity. The turn-on and turn-off input voltage thresholds are programmed using a resistor divider according to the following formulas:
3704i
9
LTC3704
APPLICATIO S I FOR ATIO
R2 VIN(OFF) = 1.248 V * 1 + R1 R2 VIN(ON) = 1.348 V * 1 + R1
+
R2
INPUT SUPPLY
OPTIONAL FILTER CAPACITOR
R1 1.248V POWER REFERENCE GND
3704 F08a
-
Figure 8a. Programming the Turn-On and Turn-Off Thresholds Using the RUN Pin
EXTERNAL LOGIC CONTROL
Figure 8b. On/Off Control Using External Logic
+
R2 1M INPUT SUPPLY
-
Figure 8c. External Pull-Up Resistor On RUN Pin for "Always On" Operation
3704i
10
U
The resistor R1 is typically chosen to be less than 1M. For applications where the RUN pin is only to be used as a logic input, the user should be aware of the 7V Absolute Maximum Rating for this pin! The RUN pin can be connected to the input voltage through an external 1M resistor, as shown in Figure 8c, for "always on" operaton.
VIN RUN COMPARATOR BIAS AND START-UP CONTROL RUN 6V
W
UU
+ -
RUN COMPARATOR RUN 6V 1.248V
+ -
3704 F08b
VIN RUN COMPARATOR
RUN 6V
+ -
GND
1.248V
3704 F08c
LTC3704
PACKAGE DESCRIPTIO
5.23 (.206) MIN
0.50 3.05 0.38 (.0197) (.0120 .0015) BSC TYP RECOMMENDED SOLDER PAD LAYOUT
0.254 (.010) GAUGE PLANE
0.18 (.007) SEATING PLANE 0.17 - 0.27 (.007 - .011) 0.13 0.05 (.005 .002)
MSOP (MS) 1001
0.50 (.0197) NOTE: TYP 1. DIMENSIONS IN MILLIMETER/(INCH) 2. DRAWING NOT TO SCALE 3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX
U
MS Package 10-Lead Plastic MSOP
(Reference LTC DWG # 05-08-1661)
0.889 0.127 (.035 .005) 3.2 - 3.45 (.126 - .136) 3.00 0.102 (.118 .004) (NOTE 3) 10 9 8 7 6 0.497 0.076 (.0196 .003) REF DETAIL "A" 0 - 6 TYP 12345 0.53 0.01 (.021 .006) DETAIL "A" 1.10 (.043) MAX 0.86 (.034) REF 4.88 0.10 (.192 .004) 3.00 0.102 (.118 .004) NOTE 4
3704i
11
LTC3704
TYPICAL APPLICATIO
C9 1nF OPTIONAL
R5 68.1k 1% RUN ITH RC 9.1k NFB CC2 330pF CC1 10nF RT 80.6k 1% FREQ MODE/SYNC LTC3704 INTVCC GATE GND SENSE VIN CIN 47F 16V CVCC 4.7F
R1 1.21k 1%
RELATED PARTS
PART NUMBER LT1175 LT(R)1619 LTC1624 LTC1700 LTC1871 LTC1872 LT1930 LT1931 LT1964 LTC3401/LTC3402 DESCRIPTION Negative Linear Low Dropout Regulator Current Mode PWM Controller Current Mode DC/DC Controller No RSENSE Synchronous Step-Up Controller No RSENSE Boost, Flyback and SEPIC Controller SOT-23 Boost Controller 1.2MHz, SOT-23 Boost Converter Inverting 1.2MHz, SOT-23 Converter ThinSOT Linear Low Dropout Regulator 1A/2A 3MHz Synchronous Boost Converters
TM
ThinSOT is a trademark of Linear Technology Corporation.
12
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 q FAX: (408) 434-0507
q
U
R4 154k 1% VIN 5V TO 15V L1* CDC 22F 25V X7R L2* M1 D1 COUT1 100F 6.3V VOUT -5V 5A
+ COUT2
150F 6.3V GND
3704 F01a
R2 3.65k 1%
CIN: TDK C5570X5R1C476M COUT1: TDK C5750X5R0J107M COUT2: PANASONIC EEFUE0J151R CDC: TDK C5750X7R1E226M CVCC: TDK C2012X5R0J475K
D1: FAIRCHILD MBR2035CT L1, L2: COILTRONICS VP5-0053 (*COUPLED INDUCTORS, WITH 3 WINDINGS IN PARALLEL ON PRIMARY AND SECONDARY) M1: INTERNATIONAL RECTIFIER IRF7822
High Efficiency Positive-to-Negative Converter
COMMENTS User-Selectable Current Limit from 200mA to 800mA, 0.4V Dropout at 500mA, 45A Operating Current 300kHz Fixed Frequency, Boost, SEPIC, Flyback Topology SO-8; 300kHz Operating Frequency; Buck, Boost, SEPIC Design; VIN Up to 36V Up to 95% Efficiency, Operation as Low as 0.9V Input 2.5V VIN 30V, Current Mode Control, Programmable fOSC from 50kHz to 1MHz Delivers Up to 5A, 550kHz Fixed Frequency, Current Mode Up to 34V Output, 2.6V VIN 16V, Miniature Design Positive-to-Negative DC/DC Conversion, Miniature Design 200mA Output Current, Low Noise, 340mV Drop Out at 200mA, 5-Lead ThinSOT Up to 97% Efficiency, Very Small Solution, 0.5V VIN 5V
3704i LT/TP 1201 1.5K * PRINTED IN USA
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2001

▲Up To Search▲

Price & Availability of LTC3704

	To Download LTC3704 Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .