Datasheet

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LT4180

4180fb

For more information www.linear.com/4180

Typical applicaTion

FeaTures DescripTion

Virtual Remote Sense

Controller

The LT

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 Sense™ 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 opto-

isolator sink capability, under/overvoltage lockout,

soft-start and a ±1% internal voltage reference. The

Virtual Remote Sense feature set includes user-program-

mable 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-lead, SSOP package.

Isolated Power Supply with Virtual Remote Sense

applicaTions

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 V

Range: 3.1V to 50V

24-Lead SSOP Package

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

L, LT , LT C , LT M, 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.

LOAD

vs V

WIRE

CAT5E CABLE

LINE

DIV0 DIV1V

OSC

COMP

DRAIN

SENSE DIV2 SPREAD CHOLD1 CHOLD2 CHOLD3 CHOLD4

4180 TA01a

RUN

OSC

SWITCHING

REGULATOR

–

LT4180

VIRTUAL REMOTE SENSE

SENSE

WIRING

(V)

LOAD

(V)

4.97

4.98

4.99

4.96

4.95

0.5 1.51 2 2.5 3

4.92

4.91

4.94

5.00

4.93

4180 TAO1b

Summary of content (18 pages)

PAGE 1
LT4180 Virtual Remote Sense Controller Features n n n n n n n n n n Description 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.
PAGE 2
LT4180 Absolute Maximum Ratings Pin Configuration (Note 1) 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.........................................
PAGE 3
LT4180 Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C, VIN = SENSE = 5V, unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN VINTVCC LDO Regulator Output Voltage in Dropout VIN = 2.5V 2.
PAGE 4
LT4180 Typical Performance Characteristics VREF vs Temperature 1.2215 204.0 3.165 3.160 3.155 INTVCC (V) 1.2205 1.2200 3.150 3.145 1.2195 5 25 45 65 85 105 125 TEMPERATURE (°C) 3.135 –55 –35 –15 4108 G01 203.0 202.5 202.0 3.140 1.2190 –55 –35 –15 ROSC = 20k COSC = 1nF 203.5 FREQUENCY (kHz) 1.2210 VREF (V) Oscillator Frequency vs Temperature INTVCC vs Temperature 5 25 45 65 85 105 125 TEMPERATURE (°C) 201.
PAGE 5
LT4180 Pin Functions INTVCC (Pin 1): The LDO Output. A low ESR ceramic capacitor provides decoupling and output compensation. 1µF or more should be used. Virtual Remote Sense. This is a high current output capable of driving opto-isolators. Other isolation methods may also be used with this output. 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. DIV2 (Pin 16): Dither Division Ratio Programming Pin.
PAGE 6
LT4180 Block Diagram 1 24 VIN INTVCC 4 – + 5 BANDGAP REF TRACK/ HOLD TRACK_HI_I CHOLD1 6 8 7 10 3 9 FB GUARD2 CHOLD2 CHOLD3 GUARD3 TRIM CIRCUIT REF_OK GND + 11 23 VPP HI_GAIN IAMP LDO 12 22 SENSE TRACK/ HOLD TRACK/ HOLD TRACK_HI_FB + – + GM2 – INST AMP TRACK/ HOLD – SPREAD GM1 SPREAD SPECTRUM CLOCK GENERATOR FB_SELECT CORRECTED _REF 20 21 DIV1 DIV2 19 18 17 16 REF TRACK_LOW_FB TRACK_DELTA_FB CHOLD4 COMP CLK MOD GUARD4 OSC 2 DIV0 OSC DRAIN OV + OV – RUN – UV +
PAGE 7
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.
PAGE 8
LT4180 Operation from degrading contacts. Making the capacitor larger can minimize the voltage ripple at the load due to a combination of load regulation and the dither frequency of the LT4180. Figure 3 shows the timing diagram for Virtual Remote Sense. A new cycle begins when the power supply and Virtual Remote Sense close the loop around VOUT (regulate VOUT = H).
PAGE 9
LT4180 Applications Information 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.
PAGE 10
LT4180 Applications Information CLOAD = RWIRE NPO ceramic or other capacitors with low leakage and dielectric absorption should be used for all HOLD capacitors. 2.2 • 2 • fDITHER 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 9.38Ω/100m conductor resistance. Maximum wiring resistance is: RWIRE = 2 • 1000ft • 0.305m/ft • 0.
PAGE 11
LT4180 Applications Information VLOAD 11.9V VLOAD 1V/DIV IDITHER 500mA/DIV IDITHER 500mA/DIV 20µs/DIV 4180 F07b Figure 7b. Dither Current and VOUT with 10nF, 37k Compensation 1.5A Load 4180 F08b Figure 8b. 500mA to 1A Transient Response Test with CHOLD4 = 47nF Nicely Damped Behavior After all the CHOLD values have been finalized, check for proper voltage drop correction and converter behavior (start-up, regulation, etc.), over the load and input voltage ranges. VLOAD 11.
PAGE 12
LT4180 Applications Information ⎛ 1.22V • 37.5k ⎞ R SERIES = ⎜ ⎟ − 6.1k = 5.34k ⎝ ⎠ 4V VIN R1 LT4180 RUN R2 R1 = 37.5k − 5.34k − 6.1k = 26.06 k FB R3 OV R4 4180 F09 Figure 9. Voltage Divider for Output Voltage, UVL and OVL The voltage divider resistors can be calculated from the following equations: V 1.22V RT = OV , R4 = 200µA 200µA Where RT is the total divider resistance and VOV is the overvoltage set point. ⎛ 5V • 6.1k ⎞ 1.22 V − ⎜ ⎟ ⎝ 37.5k ⎠ = 3.05k R3 = 5V 37.5k R2 = R SERIES − R3 = 2.
PAGE 13
LT4180 Applications Information Using Guard Rings REGULATOR 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 11.
PAGE 14
LT4180 Typical Applications 12V, 500mA Linear Regulator R1 0.2Ω 1% Q1 IRLZ440 VIN 20V C1 4.7µF 25V R3 27k R2 63.4k 1% R5 5.36k 1% R7 10k FB R6 2.2k 1% RUN C3 1µF DIV2 DIV1 DIV0 VPP INTVCC SENSE VIN OV SPREAD U2 LT4180EGN INTVCC GND INTVCC C2 1µF R4 3.
PAGE 15
For more information www.linear.com/4180 R14 8.66k 1% R9 105k 1% R6 9.1k R16 36.5k 1% RT FB SHDN/ UVLO VC SS C7 0.1µF CIN1 1µF 100V GND GATE INTVCC C4 4.7µF 50V CIN2 1µF 100V U2 LT3758 SENSE EMSE SYNC VIN VIN PULSE ENGINEERING PA1277NL VC VIN GND VIN 18V TO 72V VIN R2 10k VC C10 (OPT.) C18 2200pF 250V 1 2 3 R11 1.3k R13 5.36k 1% R10 2.74k 1% R8 523Ω 1% C11 47pF RUN 3 2 VOUT VIN C5 1µF C3 100µF 10V R5 0.
PAGE 16
LT4180 Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. GN Package 24-Lead Plastic SSOP (Narrow .150 Inch) (Reference LTC DWG # 05-08-1641 Rev B) .337 – .344* (8.560 – 8.738) 24 23 22 21 20 19 18 17 16 15 1413 .045 ±.005 .229 – .244 (5.817 – 6.198) .254 MIN .033 (0.838) REF .150 – .157** (3.810 – 3.988) .150 – .165 1 .0165 ±.0015 2 3 4 5 6 7 8 9 10 11 12 .0250 BSC RECOMMENDED SOLDER PAD LAYOUT .015 ±.004 × 45° (0.38 ±0.
PAGE 17
LT4180 Revision History REV DATE DESCRIPTION PAGE NUMBER A 6/11 Revised Typical Applications drawings Revised Electrical Characteristics Replaced curves G08 and G09 in Typical Performance Characteristics Replaced text for CHOLD Capacitor Selection and Compensation section and deleted Power Supply Current Limiting paragraph in Applications Information section B 4/13 Revised schematics 1, 13, 14, 18 2, 3 4 10, 11 14, 15, 18 4180fb Information furnished by Linear Technology Corporation is believed
PAGE 18
LT4180 Typical Application 12V 1.5A Buck Regulator E1 VIN 22V TO 36V GND + E3 C1 22µF 50V C6 0.47µF R3 100k INTVCC C5 0.1µF 50V R5 30.1k R8 68.1k 1% R7 10k R1 0.067Ω 1% C2 1µF 50V VIN BD BOOST SW RUN/SD PG FB RT VISHAY 1HLP2020CZ-11 L1, 10µH R4 61.9k 1% C7 22µF 25V D1 DFLS240 R6 3.65k 1% UI LT3685EDD SYNC VC INTVCC D2 CMDSH-3 R11 1k C4 1µF INTVCC C8 1µF FB R9 2.01k 1% R10 5.36k 1% OUTPUT TO WIRING AND LOAD 12V, 1.5A 2.