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Electrical Specifications Subject to Change
LT4180 Virtual Remote Sense Controller FEATURES
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DESCRIPTION
The LT(R)4180 solves the problem of providing tight load regulation over long, highly resistive cables without requiring an additional pair of remote sense wires. This Virtual Remote SenseTM device continuously interrogates the line impedance and corrects the power supply output voltage via its feedback loop to maintain a steady voltage at the load regardless of current changes. The LT4180 is a full-featured controller with 5mA optoisolator sink capability, under/overvoltage lockout, soft-start and a 1% internal voltage reference. The Virtual Remote Sense feature set includes user-programmable dither frequency and optional spread spectrum dither. The LT4180 works with any topology and type of isolated or nonisolated power supply, including DC/DC converters and adjustable linear regulators. The LT4180 is available in a 24-pin, SSOP package.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and Virtual Remote Sense is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners.
Tight Load Regulation with Highly Resistive Cables without Requiring Remote Sense Wiring Compatible with Isolated and Nonisolated Power Supplies 1% Internal Voltage Reference 5mA Sink Current Capability Soft-Correct Reduces Turn-On Transients Undervoltage and Overvoltage Protection Pin-Programmable Dither Frequency Optional Spread Spectrum Dither Wide VIN Range: 3.1V to 50V 24-Pin SSOP Package
APPLICATIONS
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12V High Intensity Lamps 28V Industrial Systems High Power (>40 Watts) CAT5 Cable Systems Wiring Drop Cancellation for Notebook Computer Battery Charging AC and DC Adaptors Well-Logging and Other Remote Instrumentation Surveillance Equipment
TYPICAL APPLICATION
Isolated Power Supply with Virtual Remote Sense
CAT5E CABLE RSENSE + CL SWITCHING REGULATOR VC VIN - LINE VLOAD (V) RL LINE 5.00 4.99 4.98 4.97 4.96 4.95 4.94 4.93 4.92
4180 TA01a
VLOAD vs VWIRE
SENSE DIV0 DIV1 DIV2 SPREAD CHOLD1 CHOLD2 CHOLD3 CHOLD4 LT4180 ROSC DRAIN VIRTUAL REMOTE SENSE COMP COSC OV RUN FB
4.91
0
0.5
1
1.5 VWIRING (V)
2
2.5
4180 TAO1b
3
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LT4180 ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW INTVCC DRAIN COMP CHOLD1 GUARD2 CHOLD2 GUARD3 CHOLD3 GUARD4 1 2 3 4 5 6 7 8 9 24 VIN 23 VPP 22 SENSE 21 RUN 20 OV 19 SPREAD 18 DIV0 17 DIV1 16 DIV2 15 OSC 14 ROSC 13 COSC
VIN ............................................................. -0.3V to 52V SENSE.......................................................VIN - 0.3V to VIN INTVCC, RUN, FB, OV, ROSC, OSC, DIV0, DIV1, DIV2, SPREAD, CHOLD1, CHOLD2, CHOLD3, CHOLD4, DRAIN, COMP, GUARD2, GUARD3, GUARD4, VPP ............ -0.3V to 5.5V VIN Pin Current.......................................................10mA INTVCC Pin Current .............................................-10mA COSC Pin Current..................................................3.3mA Maximum Junction Temperature .......................... 125C Operating Junction Temperature Range (Note 2) E-, I-Grades ....................................... -40C to 125C MP-Grade .......................................... -55C to 125C Storage Temperature Range .................. -65C to 125C
CHOLD4 10 FB 11 GND 12
GN PACKAGE 24-LEAD NARROW PLASTIC SSOP TJMAX = 150C, JA = 85C/W
ORDER INFORMATION
LEAD FREE FINISH LT4180EGN#PBF LT4180IGN#PBF LT4180MPGN#PBF TAPE AND REEL LT4180EGN#TRPBF LT4180IGN#TRPBF LT4180MPGN#TRPBF PART MARKING* LT4180GN LT4180GN LT4180GN PACKAGE DESCRIPTION 24-Lead Narrow Plastic SSOP 24-Lead Narrow Plastic SSOP 24-Lead Narrow Plastic SSOP TEMPERATURE RANGE -40C to 125C -40C to 125C -55C to 125C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. 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
SYMBOL VIN IVIN VREF ILIM VOL VINTVCC PARAMETER Operating Supply Voltage Input Quiescent Current Reference Voltage Open-Drain Current Limit DRAIN Low Voltage LDO Regulator Output Voltage
The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C, VIN = SENSE = 5V, unless otherwise noted.
CONDITIONS
l
MIN 3.10
l l
TYP 1
MAX 50 2 1.233 1.245 15 0.3
UNITS V mA V V mA V V
ROSC Open, COSC Open, SENSE = VIN VCHOLD2 = VCHOLD3 = 1.2V, Measured at CHOLD4 During Track VOUT Clock Phase With FB = VREF + 200mV, OSC Stopped with Voltage Feedback Loop Closed VIN = 3V VIN = 5V
1.209 1.197 5
1.221 1.221 10
3.15
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LT4180 ELECTRICAL CHARACTERISTICS
SYMBOL VINTVCC VOV VOHYST VRUN VRHYST IFB VOS PARAMETER LDO Regulator Output Voltage in Dropout Overvoltage Threshold Overvoltage Input Hysteresis Run Threshold Run Input Hysteresis Input Bias Current Current Amplifier Offset Voltage VIN = 3.5V VIN = 5V VIN = 48V A VL/A VH, A V Measured in V/V Measured at SENSE with SENSE = VIN Measured at CHOLD1 with VCHOLD1 = 1.2V Measured at CHOLD2 with VCHOLD2 = 1.2V Measured at CHOLD3 with VCHOLD3 = 1.2V Measured at CHOLD4 with VCHOLD4 = 1.5V, VCHOLD2 = 1V, VCHOLD3 = 1.2V Measured at CHOLD4 with VCHOLD4 = 1.5V, VCHOLD2 = 1.4V, VCHOLD3 = 1.2V ISC ILKG1 ILKG2 ILKG3 ILKG4 fOSC gmFB gmIAMP Soft-Correct Current Track/Hold Leakage Current Track/Hold Leakage Current Track/Hold Leakage Current Track/Hold Leakage Current Oscillator Frequency Voltage Error Amplifier Transconductance Current Amplifier Transconductance Measured at CHOLD4 Measured at CHOLD1 with VCHOLD1 = 1.2V Measured at CHOLD2 with VCHOLD2 = 1.2V Measured at CHOLD3 with VCHOLD3 = 1.2V Measured at CHOLD4 with VCHOLD4 = 1.2V ROSC = 20k, COSC = 1nF Measured from FB to COMP VCOMP = 2V, , OSC Stopped with Voltage Feedback Loop Closed Measured from SENSE to COMP VCOMP = 2V, , OSC Stopped with Current Feedback Loop Closed 170 200 110 750
The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C, VIN = SENSE = 5V, unless otherwise noted.
CONDITIONS VIN = 2.5V Rising VRISING - VFALLING Falling VRISING - VFALLING 20 -0.2 -4 -3 -4 0.891 -1 9.7 10 60 25 25 10 -200 1.5 1 1 1 1 230 0.9 20 1.21 80 0.2 4 3 4 0.909 1 10.3 A V/V A A A A A A A A A A kHz mho mho MIN 2.2 1.21 80 TYP MAX UNITS V V mV V mV A mV mV mV
A V(RATIO) ISENSE AV ICHOLD1 ICHOLD2 ICHOLD3 ICHOLD4
Current Amplifier Gain Ratio Current Amplifier Input Bias Current VFB Amplifier Gain Track/Hold Charging Current Track/Hold Charging Current Track/Hold Charging Current Track/Hold Charging Current
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. Note 2. The LT4180E is guaranteed to meet performance specifications from 0C to 125C junction temperature. Specifications over the -40C
to 125C operating junction temperature range are assured by design characterization and correlation with statistical process controls. The LT4180I is guaranteed over the full -40C to 125C operating junction temperature range. The LT4180MP is guaranteed over the full -55C to 125C operating junction temperature range. Note 3. Positive current is defined as flowing into a pin.
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LT4180 TYPICAL PERFORMANCE CHARACTERISTICS
VREF vs Temperature
1.2215 3.165 3.160 3.155 INTVCC (V) VREF (V) 1.2205 3.150 3.145 1.2195 3.140 3.135 -55 -35 -15 FREQUENCY (kHz)
INTVCC vs Temperature
204.0
Oscillator Frequency vs Temperature
ROSC = 20k COSC = 1nF
1.2210
203.5
203.0
1.2200
202.5
202.0
1.2190 -55 -35 -15
5 25 45 65 85 105 125 TEMPERATURE (C)
4108 G01
5 25 45 65 85 105 125 TEMPERATURE (C)
4108 G02
201.5 -55 -35 -15
5 25 45 65 85 105 125 TEMPERATURE (C)
4108 G03
IDRAIN vs VDRAIN
14 12 10 IDRAIN (mA) 8 6 4 2 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 VDRAIN (V) 1
4180 G04
Normal Timing
500mV/DIV CHOLD1 WITH 15k PULL-DOWN 500mV/DIV CHOLD1 WITH 15k PULL-DOWN
Spread Spectrum Timing
2V/DIV OSC
4180 G05
2V/DIV OSC
4180 G06
5s/DIV TRIGGERED ON CHOLD1
1s/DIV TRIGGERED ON OSC
VLOAD vs VWIRE
5.00 4.99 4.98 4.97 VLOAD (V) 4.96 4.95 4.94 4.93 4.92 4.91 0 0.5 1 1.5 VWIRING (V)
4180 G07
Load Step in 12V Linear Application
RWIRE = 4 CL = 100F VSENSE 2V/DIV VLOAD 2V/DIV VOUT 2V/DIV VLOAD 2V/DIV ILOAD 500mA/DIV
Load Step in Buck Application
1.2A 200mA
4180 G09
ILOAD 200mA/DIV 2ms/DIV 200mA TO 700mA LOAD TRANSIENT 100F LOAD CAP 2 2.5 3
4180 G08
5ms/DIV
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LT4180 PIN FUNCTIONS
INTVCC (Pin 1): The LDO Output. A low ESR ceramic capacitor provides decoupling and output compensation. 1F or more should be used. DRAIN (Pin 2): Open-Drain of the Output Transistor. This pin drives either the LED in an opto-isolator, or pulls down on the regulator control pin. COMP (Pin 3): Gate of the Output Transistor. This pin allows additional compensation. It must be left open if unused. CHOLD1 (Pin 4): Connects to track/hold amplifier hold capacitor. The other end of this capacitor should be Kelvin connected to GND. GUARD2 (Pin 5): Guard Ring Drive for CHOLD2. CHOLD2 (Pin 6): Connects to track/hold amplifier hold capacitor. The other end of this capacitor should be Kelvin connected to GND. GUARD3 (Pin 7): Guard Ring Drive for CHOLD3. CHOLD3 (Pin 8): Connects to track/hold amplifier hold capacitor. The other end of this capacitor should be Kelvin connected to GND. GUARD4 (Pin 9): Guard Ring Drive for CHOLD4. CHOLD4 (Pin 10): Connects to track/hold amplifier hold capacitor. The other end of this capacitor should be Kelvin connected to GND. FB (Pin 11): Receives the feedback voltage from an external resistor divider across the main output. An (optional) capacitor to ground may be added to eliminate high frequency noise. The time constant for this RC network should be no greater than 0.1 times the dither frequency. For example, with fDITHER = 1kHz, = 0.1ms. GND (Pin 12): Ground. COSC (Pin 13): Oscillator Timing Capacitor. Oscillator frequency is set by this capacitor and ROSC. For best accuracy, the minimum recommended capacitance is 100pF . ROSC (Pin 14): Oscillator Timing Resistor. Oscillator frequency is set by this resistor and COSC. OSC (Pin 15): Oscillator Output. This output may be used to synchronize the switching regulator to the Virtual Remote Sense. This is a high current output capable of driving opto-isolators. Other isolation methods may also be used with this output. DIV2 (Pin 16): Dither Division Ratio Programming Pin. DIV1 (Pin 17): Dither Division Ratio Programming Pin. DIV0 (Pin 18): Dither Division Ratio Programming Pin. Use the following table to program the dither division ratio (fOSC /fDITHER)
Table 1. Programming the Dither Division Ratio (fOSC /fDITHER)
DIV2 0 0 0 0 1 1 1 1 DIV1 0 0 1 1 0 0 1 1 DIV0 0 1 0 1 0 1 0 1 DIVISION RATIO 8 16 32 64 128 256 512 1024
For example, fDITHER = fOSC/128 with DIV2 = 1 and DIV1 = DIV0 = 0. SPREAD (Pin 19): Spread Spectrum Enable Input. Dither phasing is pseudo-randomly adjusted when SPREAD is tied high. OV (Pin 20): Overvoltage Comparator Input. This prevents line drop correction when wiring drops would cause excessive switching power supply output voltage. Set OV so VREG(MAX) 1.50VLOAD. RUN (Pin 21): The RUN pin provides the user with an accurate means for sensing the input voltage and programming the start-up threshold for the line drop corrector. SENSE (Pin 22): Current Sense Input. This input connects to the current sense resistor. Kelvin connect to RSENSE. VPP (Pin 23): Connect this pin to INTVCC. VIN (Pin 24): Main Supply Pin. VIN must be locally bypassed to ground. Kelvin connect the current sense resistor to this pin and minimize interconnect resistance.
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LT4180 BLOCK DIAGRAM
1 24 VIN INTVCC 22 SENSE IAMP 23 VPP TRIM CIRCUIT
LDO 12 GND REF_OK BANDGAP REF
4
CHOLD1
11 5 6 8 7 10 3
FB GUARD2 CHOLD2 CHOLD3 GUARD3 TRACK_HI_FB INST AMP TRACK/ HOLD REF TRACK_LOW_FB TRACK_DELTA_FB CORRECTED _REF
GM1
TRACK/ HOLD TRACK/ HOLD
+ GM2 -
+ -
CHOLD4 COMP CLK GUARD4 MOD OSC OSC 15
9
2 20
DRAIN OV
+ OV - - UV +
OVERVOLTAGE
21
RUN
UNDERVOLTAGE ROSC 14 COSC 13
4180 BD
6
-
-
+
+
HI_GAIN
TRACK/ HOLD TRACK_HI_I SPREAD DIV0 SPREAD SPECTRUM CLOCK GENERATOR DIV1 DIV2
19 18 17 16
FB_SELECT
RLIM
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LT4180 OPERATION
Voltage drops in wiring can produce considerable load regulation errors in electrical systems (Figure 1). As load current, IL , increases the voltage drop in the wiring (IL * RW) increases and the voltage delivered to the system (VL) drops. The traditional approach to solving this problem, remote sensing, regulates the voltage at the load, increasing the power supply voltage (VOUT) to compensate for voltage drops in the wiring. While remote sensing works well, it does require an additional pair of wires to measure at the load, which may not always be practical. The LT4180 eliminates the need for a pair of remote sense wires by creating a Virtual Remote Sense. Virtual remote sensing is achieved by measuring the incremental change in voltage that occurs with an incremental change in current in the wiring (Figure 2). This measurement can then be used to infer the total DC voltage drop in the wiring, which can then be compensated for. The Virtual Remote Sense takes over control of the power supply via the feedback
IL POWER SUPPLY RW
pin (VFB) of the power supply maintaining tight regulation of load voltage, VL. Figure 3 shows the timing diagram for virtual remote sensing (VRS). A new cycle begins when the power supply and VRS close the loop around VOUT (regulate VOUT = H). Both VOUT and IOUT slew and settle to a new value, and these values are stored in the Virtual Remote Sense (track VOUT high = L and track IOUT = L). The VOUT feedback loop is opened and a new feedback loop is set up commanding the power supply to deliver 90% of the previously measured current (0.9IOUT). VOUT drops to a new value as the power supply reaches a new steady state, and this information is also stored in the Virtual Remote Sense. At this point, the change in output voltage (VOUT) for a -10% change in output current has been measured and is stored in the Virtual Remote Sense. This voltage is used during the next VRS cycle to compensate for voltage drops due to wiring resistance.
IL
+ -
+
VL
SYSTEM
POWER SUPPLY
RW
+
POWER WIRING
+
VL
SYSTEM
VOUT POWER WIRING
VOUT VFB
4180 F01
-
-
-
REMOTE SENSE WIRING VIRTUAL REMOTE SENSE
4180 F02
Figure 1. Traditional Remote Sensing
Figure 2. Virtual Remote Sensing
VOUT REGULATE VOUT TRACK VOUT HIGH TRACK IOUT REGULATE IOUT LOW TRACK VOUT LOW TRACK VOUT
4180 F03
Figure 3. Simplified Timing Diagram, Virtual Remote Sense
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LT4180 APPLICATIONS INFORMATION
INTRODUCTION The LT4180 is designed to interface with a variety of power supplies and regulators having either an external feedback or control pin. In Figure 4, the regulator error amplifier (which is a gm amplifier) is disabled by tying its inverting input to ground. This converts the error amplifier into a constant-current source which is then controlled by the drain pin of the LT4180. This is the preferred method of interfacing because it eliminates the regulator error amplifier from the control loop which simplifies compensation and provides best control loop response.
REGULATOR LT4180
DESIGN PROCEDURE The first step in the design procedure is to determine whether the LT4180 will control a linear or switching supply/regulator. If using a switching power supply or regulator, it is recommended that the supply be synchronized to the LT4180 by connecting the OSC pin to the SYNC pin (or equivalent) of the supply. If the power supply is synchronized to the LT4180, the power supply switching frequency is determined by: 4 fOSC = ROSC * COSC Recommended values for ROSC are between 20k and 100k (with 30.1k the optimum for best accuracy) and greater than 100pF for COSC. COSC may be reduced to as low as 50pF but oscillator frequency accuracy will be somewhat , degraded. The following example synchronizes a 250kHz switching power supply to the LT4180. In this example, start with ROSC = 30.1k: COSC = 4 = 531pF 250kHz * 30 . 1k
+ -
ITH OR VC
DRAIN
4180 F04
Figure 4. Nonisolated Regulator Interface
For proper operation, increasing control voltage should correspond to increasing regulator output. For example, in the case of a current mode switching power supply, the control pin ITH should produce higher peak currents as the ITH pin voltage is made more positive. Isolated power supplies and regulators may also be used by adding an opto-coupler (Figure 5). LT4180 output voltage INTVCC supplies power to the opto-coupler LED. In situations where the control pin VC of the regulator may exceed 5V, a cascode may be added to keep the DRAIN pin of the LT4180 below 5V (Figure 6). Use a Low VT MOSFET for the cascode transistor.
REGULATOR INTVCC LT4180
This example uses 470pF For 250kHz: . ROSC = 4 = 34 . 04k 250kHz * 470pF
The closest standard 1% value is 34k. The next step is to determine the highest practical dither frequency. This may be limited either by the response time of the power supply or regulator, or by the propagation time of the wiring connecting the load to the power supply or regulator.
TO VC > 5V COMP
+ -
VC
OPTO-COUPLER
DRAIN
4180 F05
LT4180 INTVCC
Figure 5. Isolated Power Supply Interface
DRAIN
4180 F06
Figure 6. Cascoded DRAIN Pin for Isolated Supplies
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LT4180 APPLICATIONS INFORMATION
First determine the settling time (to 1% of final value) of the power supply. The settling time should be the worst-case value (over the whole operating envelope: VIN, ILOAD, etc.). 1 F1 = Hz 2 * t SETTLING For example, if the power supply takes 1ms to settle (worst-case) to within 1% of final value: F1 = 1 = 500Hz 2 * 1e - 3 Continuing this example, the dither frequency should be less than 500Hz (limited by the power supply). With the dither frequency known, the division ratio can be determined: f 250, 000 DRATIO = OSC = = 500 500 fDITHER The nearest division ratio is 512 (set DIV0 = L, DIV1 = DIV2 = H). Based on this division ratio, nominal dither frequency will be: f 250, 000 f DITHER = OSC = = 488 Hz 512 DRATIO After the dither frequency is determined, the minimum load decoupling capacitor can be determined. This load capacitor must be sufficiently large to filter out the dither signal at the load. 2.2 CLOAD = R WIRE * 2 * f DITHER Where CLOAD is the minimum load decoupling capacitance, RWIRE is the minimum wiring resistance of one conductor of the wiring pair, and fDITHER is the minimum dither frequency. Continuing the example, our CAT5 cable has a maximum 9.38/100m conductor resistance. Maximum wiring resistance is: RWIRE = 2 * 1000ft * 0.305m/ft * 0.0938/m RWIRE = 57.2
Next, determine the propagation time of the wiring. In order to ignore transmission line effects, the dither period should be approximately twenty times longer than this. This will limit dither frequency to: VF F2 = Hz 20 * 1. 017ns /ft * L Where VF is the velocity factor (or velocity of propagation), and L is the length of the wiring (in feet). For example, assume the load is connected to a power supply with 1000ft of CAT5 cable. Nominal velocity of propagation is approximately 70%. F2 = 0.7 = 34 . 4 kHz 20 * 1. 017e - 9 * 1000
The maximum dither frequency should not exceed F1 or F2 (whichever is less): fDITHER < min (F1, F2).
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LT4180 APPLICATIONS INFORMATION
With an oscillator tolerance of 15%, the minimum dither frequency is 414.8Hz, so the minimum decoupling capacitance is: CLOAD = 2.2 = 46 . 36F 57 . 2 * 2 * 414 . 8Hz is observed, decrease the value of the resistor until it just disappears. If overshoot or ringing is not observed, increase the value of the resistor until it is observed, then slightly decrease the value of the resistor so that overshoot and ringing disappear. Check for proper voltage drop correction and converter behavior (start-up, regulation etc.), over the load range, and repeat the above procedure with a smaller value of the compensation capacitor, if necessary. Decrease CHOLD4 capacitance until VOUT exhibits slight low frequency instability, then increase CHOLD4 slightly from this value. Setting Output Voltage, Undervoltage and Overvoltage Thresholds The RUN pin has accurate rising and falling thresholds which may be used to determine when Virtual Remote Sense operation begins. Undervoltage threshold should never be set lower than the minimum operating voltage of the LT4180 (3.1V). The overvoltage threshold should be set slightly greater than the highest voltage which will be produced by the power supply or regulator: VOUT(MAX) = VLOAD(MAX) + VWIRE(MAX) VOUT(MAX) should never exceed 1.5 * VLOAD Since the RUN and OV pins connect to MOSFET input comparators, input bias currents are negligible and a common voltage divider can be used to set both thresholds (Figure 7).
VIN R1 LT4180 RUN
This is the minimum value. Select a nominal value to account for all factors which could reduce the nominal, such as initial tolerance, voltage and temperature coefficients and aging. CHOLD Capacitor Selection and Compensation With dither frequency determined, use the following equations to determine CHOLD values: 11 . 9nF CHOLD1 = fDITHER (kHz) and CHOLD2 = CHOLD3 = 2 . 5nF fDITHER (kHz)
So, with a dither frequency of 488Hz: CHOLD1 = and CHOLD2 = CHOLD3 = 2 . 5nF = 5 . 12nF 0 . 488(kHz) 11 . 9nF = 24 . 4nF 0 . 488kHz
NPO ceramic or other capacitors with low leakage and dielectric absorption should be used for all hold capacitors. . Set CHOLD4 to 1F Start with a 47pF capacitor between the COMP and DRAIN pins of the LT4180. Add an RC network in parallel with the 47pF capacitor. 10k and 10nF are good starting values. Connect a DC load corresponding to full-scale load current and verify that VOUT produces a rounded squarewave without any noticeable overshoot or ringing (similar to the VOUT waveform in Figure 3). If overshoot or ringing
R2 FB R3 OV R4
4180 F07
Figure 7. Voltage Divider for Output Voltage, UVL and OVL
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LT4180 APPLICATIONS INFORMATION
The voltage divider resistors can be calculated from the following equations: V 1 . 22V R T = OV , R4 = 200 A 200 A Where RT is the total divider resistance and VOV is the overvoltage set point. Find the equivalent series resistance for R2 and R3 (RSERIES). This resistance will determine the RUN voltage level. 1 . 22 * R T RSERIES = - R4 VUVL R1 = R T - RSERIES - R4 R4 1 . 22 V - VOUT(NOM) * RT R3 = VOUT(NOM) RT R2 = RSERIES - R3 Where VUVL is the RUN voltage and VOUT(NOM) is the nominal output voltage desired. , , For example, with VUVL = 4V VOV = 7.5V and VOUT(NOM) = 5V RT = R4 = 7 . 5V = 37 . 5 k 200A 1 . 22V = 6 . 1k 200 A RSENSE SELECTION Select the value of RSENSE so that it produces a 100mV voltage drop at maximum load current. For best accuracy, VIN and SENSE should be Kelvin connected to this resistor. Soft-Correct Operation The LT4180 has a soft-correct function which insures orderly start-up. When the RUN pin rising threshold is first exceeded (indicating VIN has crossed its undervoltage lockout threshold), power supply output voltage is set to a value corresponding to zero wiring voltage drop (no correction for wiring). Over a period of time (determined by CHOLD4), the power supply output voltage ramps up to account for wiring voltage drops, providing best load-end voltage regulation. A new soft-correct cycle is also initiated whenever an overvoltage condition occurs.
5V POWER SUPPLY OUTPUT VOLTAGE 10Vw POWER SUPPLY INPUT VOLTAGE
4180 F08
200ms/DIV
Figure 8. Soft-Correct Operation, CHOLD4 = 1F
1 . 22V * 37 . 5k RSERIES = - 6 . 1k = 5 . 34k 4V R1 = 37 . 5 k - 5 . 3 4 k - 6 . 1k = 26 . 06 k 5V * 6 . 1k 1 . 22 V - 37 . 5 k = 3 . 05 k R3 = 5V 37 . 5 k R2 = RSERIES - R3 = 2 . 29 k
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LT4180 APPLICATIONS INFORMATION
Using Guard Rings The LT4180 includes a total of four track/holds in the Virtual Remote Sense path. For best accuracy, all leakage sources on the CHOLD pins should be minimized. At very low dither frequencies, the circuit board layout may include guard rings which should be tied to their respective guard ring drivers. To better understand the purpose of guard rings, a simplified model of hold capacitor leakage (with and without guard rings) is shown in Figure 9. Without guard rings, a large difference voltage may exist between the hold capacitor (Pin 1) node and adjacent conductors (Pin 2) producing substantial leakage current through the leakage resistance (RLKG). By adding a guard ring driver with approximately the same voltage as the voltage on the hold capacitor node, the difference voltage across RLKG1 is reduced substantially thereby reducing leakage current on the hold capacitor. Synchronization Linear and switching power supplies and regulators may be used with the LT4180. In most applications regulator interference should be negligible. For those applications where accurate control of interference spectrum is desirable, an oscillator output has been provided so that
RLKG
switching supplies may be synchronized to the LT4180 (Figure 10). The OSC pin was designed so that it may directly connect to most regulators, or drive opto-isolators (for isolated power supplies). Spread Spectrum Operation Virtual remote sensing relies on sampling techniques. Because switching power supplies are commonly used, the LT4180 uses a variety of techniques to minimize potential interference (in the form of beat notes which may occur between the dither frequency and power supply switching frequency). Besides several types of internal filtering, and the option for VRS/power supply synchronization, the LT4180 also provides spread spectrum operation. By enabling spread spectrum operation, low modulation index pseudo-random phasing is applied to Virtual Remote Sense timing. This has the effect of converting any remaining narrow-band interference into broadband noise, reducing its effect. Increasing Voltage Correction Range Correction range may be slightly improved by regulating INTVCC to 5V. This may be done by placing an LDO between VIN and INTVCC. Contact Linear Technology Applications for more information.
RLKG1 RLKG2
1
2
1 WITH GUARD RING
2
WITHOUT GUARD RING
4180 F09
Figure 9. Simplified Leakage Models (with and without Guard Rings)
REGULATOR SYNC
LT4180 OSC
4180 F10
Figure 10. Clock Interface for Synchronization
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LT4180 TYPICAL APPLICATIONS
12V, 500mA Linear Regulator
R1 0.1 1% C1 4.7F 25V R2 63.4k 1% R4 3.74k 1% R5 5.36k 1% R7 10k INTVCC DRAIN C5 22pF C6 1nF COMP GND CHOLD1 GUARD2 CHOLD2 GUARD3 CHOLD3 GUARD4 CHOLD4 C7 4.7nF C8 470pF C9 470pF COSC C10 10nF OSC ROSC R9 41.7k 1%
4180 TA02
VIN 20V
Q1 IRLZ440
OUTPUT TO WIRING AND LOAD 500mA 8 MAX RWIRE 330F LOAD CAPACITANCE
INTVCC C3 1F
R3 27k
C2 1F FB RUN VIN SENSE U2 LT4180EGN DIV2 DIV1 DIV0 VPP INTVCC
C4 10F 25V
R6 2.2k 1%
OV
SPREAD
GND
Q2 VN2222
R8 20k
C11 470pF
12V, 600mA Boost Regulator
D1 DFLS220 C2 10F 25V R3 61.9k 1% R5 3.65k 1% R7 2k 1% R9 5.36k 1% R13 1.5k C3 1F FB RUN VIN SENSE R1 0.05 1% R2 191k
L1 4.7H VIN 5V VISHAY C1 IHLP2525CZ-11 4.7F 16V R4 100k R6 24.3k
OUTPUT TO WIRING AND LOAD (100mA MINIMUM) 600mA, 6 MAX RWIRE 470F LOAD CAPACITANCE C4 1F
INTVCC
GATE SW1 SW1 SW1 SW2 SW2 SW2 VCC SHDN FAULT U1 LT3581EMSE SS CLKOUT R10 84.5k C6 0.1F FB VC GND
DIV2 DIV1 DIV0 VPP INTVCC SPREAD OSC COSC ROSC R12 41.7k 1%
4180 TA03
R8 10k GND
SYNC RT
U2 LT4180EGN OV DRAIN COMP GND CHOLD1 GUARD2 CHOLD2 GUARD3 CHOLD3 GUARD4 CHOLD4 C7 47pF C9 4.7nF C10 470pF C12 10nF C11 470pF
C13 470pF
R11 10k 1%
C8 1nF
4180fp
13
LT4180
14
3.3V Isolated Flyback Regulator
VIN VOUT T1 CIN2 1F 100V C2 4700pF R2 10k D1 BAV21W 3 78 R3 51.1 1% 1 PA1277NL R5 0.018 1% C5 1F FB RUN VIN SENSE U1 LT4180EGN DIV2 D3 BAS516 2 32 D2 UPS840 100F 10V 56 C3 100F 10V C4 4.7F 50V 4 OUTPUT TO WIRING AND LOAD 3.3V, 3A 0.4 MAX RWIRE 1000F LOAD CAPACITANCE
VIN 18V TO 72V
TYPICAL APPLICATIONS
GND
CIN1 1F 100V
R6 17.4k 5678 Q1 Si4848DY R7, 1 INTVCC 123 R12 100 C10 (OPT.) RCS1 0.040 C8 0.01F R11 2k R13 5.36k 1% C11 47pF VC U3 PS2801-1 R10 2.74k 1% INTVCC2 R8 523 1% GATE R4 13.3k 1%
VIN
C7 0.1F
VIN
INTVCC2
VC
R9 105k 1%
SS
VIN
VC
C6 1F DIV1 DIV0 VPP INTVCC SPREAD OSC COSC ROSC C13 470pF C15 C14 0.1F 470pF R15 41.2k 1% OSC
SHDN/ UVLO
U2 LT3758 SENSE EMSE SYNC
C9 100pF
FB
RT
GND
R14 8.66k 1%
R16 36.5k 1%
OV DRAIN COMP GND CHOLD1 GUARD2 CHOLD2 GUARD3 CHOLD3 GUARD4 CHOLD4
C12 4.7nF (NANO) R17 20k 1% C17 3.3nF
C16 470pF
C18 2200pF 250V
4180 TA04
PULSE ENGINEERING PA1277NL
4180fp
LT4180 PACKAGE DESCRIPTION
GN Package 24-Lead Plastic SSOP (Narrow .150 Inch)
(Reference LTC DWG # 05-08-1641)
.337 - .344* (8.560 - 8.738) 24 23 22 21 20 19 18 17 16 15 1413
.045 .005
.033 (0.838) REF
.229 - .244 (5.817 - 6.198)
.254 MIN .150 - .165
.150 - .157** (3.810 - 3.988)
1
.0165 .0015 RECOMMENDED SOLDER PAD LAYOUT .0250 BSC
23
4
56
7
8
9 10 11 12
.015 .004 x 45 (0.38 0.10)
.0075 - .0098 (0.19 - 0.25) 0 - 8 TYP
.0532 - .0688 (1.35 - 1.75)
.004 - .0098 (0.102 - 0.249)
.016 - .050 (0.406 - 1.270)
NOTE: 1. CONTROLLING DIMENSION: INCHES INCHES 2. DIMENSIONS ARE IN (MILLIMETERS) 3. DRAWING NOT TO SCALE *DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE **DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
.008 - .012 (0.203 - 0.305) TYP
.0250 (0.635) BSC
GN24 (SSOP) 0204
4180fp
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.
15
LT4180 TYPICAL APPLICATION
12V 1.5A Buck Regulator
VIN 22V TO 36V GND E3 E1
+
C1 22F 50V R3 100k
C2 1F 50V C6 0.47F VIN BD BOOST SW RUN/SD PG FB RT UI LT3685EDD VISHAY 1HLP2020CZ-11 L1, 10H C7 22F 25V D1 DFLS240 INTVCC VC D2 CMDSH-3 R11 1k R4 61.9k 1% R6 3.65k 1% R9 2.01k 1% R10 5.36k 1% C4 1F
R1 0.033 1%
OUTPUT TO WIRING AND LOAD 12V, 1.5A 2.5 MAX RWIRE 470F LOAD CAPACITANCE
INTVCC C8 1F
INTVCC R5 30.1k
C5 0.1F 50V
FB
RUN
VIN
SENSE LT4180EGN
DIV2
DIV1 DIV0
VPP INTVCC SPREAD
R7 10k
R8 68.1k 1%
SYNC
OV DRAIN COMP GND CHOLD1 GUARD2 CHOLD2 GUARD3 CHOLD3 GUARD4 CHOLD4 C9 47pF C10 4.7nF C11 470pF C13 10nF C12 470pF
OSC COSC ROSC R12 22.1k 1%
4180 TA05
C14 330pF
R13 17.4k 1%
C15 1.5nF
RELATED PARTS
PART NUMBER LT3581 LT3685 LT3573 LT3757 LT3758 LTC3805/ LTC3805-5 DESCRIPTION Boost/Inverting DC/DC Converter with 3.3A Switch, Soft-Start and Synchronization 36V, 2A, 2.4MHz Step-Down Switching Regulator Isolated Flyback Switching Regulator with 60V Integrated Switch Boost, Flyback, SEPIC and Inverting Controller Boost, Flyback, SEPIC and Inverting Controller Adjustable Fixed 70kHz to 700kHz Operating Frequency Flyback Controller COMMENTS 2.5V VIN 22V, Current Mode Control, 200kHz to 2.5MHz, MSOP-16E and 3mm x 4mm DFN-14 Packages 3.6V VIN 36V (60VPK), Integrated Boost Diode, MSOP-10E and 3mm x 3mm DFN Packages 3V VIN 40V, Up to 7W, No Opto-Isolator or Third Winding Required, MSOP-16E Package 2.9V VIN 40V, Current Mode Control, 100kHz to 1MHz Programmable Operation Frequency, MSOP-10E and 3mm x 3mm DFN-10 Packages 5.5V VIN 100V, Current Mode Control, 100kHz to 1MHz Programmable Operation Frequency, MSOP-10E and 3mm x 3mm DFN-10 Packages VIN and VOUT Limited Only by External Components, MSOP-10E and 3mm x 3mm DFN-10 Packages
4180fp
16 Linear Technology Corporation
(408) 432-1900 FAX: (408) 434-0507
LT 0310 * PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2010

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