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Table Of Contents

LT6110

6110fa

For more information www.linear.com/LT6110

Typical applicaTion

FeaTures DescripTion

Cable/Wire Drop

Compensator

The LT

6110 is a precision high side current sense with a

current mode output, designed for controlling the output

voltage of an adjustable power supply or voltage regulator.

This can be used to compensate for drops in voltage at

a remote load due to resistance in a wire, trace or cable.

The LT6110 monitors load current via a series-connected

internal or external sense resistor. Tw o current mode out

puts, one sinking and one sourcing, are provided that are

proportional

to the load current. This allows the LT6110 to

adjust the output voltage of a wide variety of regulators.

Either output may be used to monitor the load current.

Low DC offset allows for the use of a small sense resis

tor, as

well as precise control of small variations in wire

voltage drop.

L, LT , LT C , LT M , Linear Technology, the Linear logo and µModule are registered trademarks

and ThinSOT is a trademark of Linear Technology Corporation. All other trademarks are the

property of their respective owners.

applicaTions

Improve Voltage Regulation to a Remote Load by 10×

Ideal for Resistor-Adjustable Voltage Regulators

Gain Configurable with a Single Resistor

High Side Current Sensing:

Integrated 20mΩ Sense Resistor for Up to 3A

Ability to Use an External Sense Resistor

300µV Maximum Input Offset Voltage

Output Current Accuracy of 1% Maximum

30µA Maximum Supply Current

2V to 50V Supply Range

Fully Specified from –40°C to 125°C

Available in Low Profile (1mm) ThinSOT™ and

(2mm × 2mm) DFN Packages

Automotive and Industrial Power Distribution

USB Power

DC/DC Converters

Plug-In DC Adapters

Power over Ethernet

IOUT

+IN –IN

LT6110

–

IMON

–

REG

LOAD

WIRE

LOAD

6110 TA01

500mV/DIV

LOAD

COMPENSATED

LOAD

UNCOMPENSATED

LOAD

200µs/DIV

OUT

REGULATOR

GND

REMOTE

LOAD

Summary of content (38 pages)

PAGE 1
LT6110 Cable/Wire Drop Compensator Features n n n n n n n n n n Description Improve Voltage Regulation to a Remote Load by 10× Ideal for Resistor-Adjustable Voltage Regulators Gain Configurable with a Single Resistor High Side Current Sensing: Integrated 20mΩ Sense Resistor for Up to 3A Ability to Use an External Sense Resistor 300µV Maximum Input Offset Voltage Output Current Accuracy of 1% Maximum 30µA Maximum Supply Current 2V to 50V Supply Range Fully Specified from –40°C to 125°C Available in Low Pr
PAGE 2
LT6110 Absolute Maximum Ratings (Note 1) Total Supply Voltage (V+ to V–)..................................55V +IN, –IN, IOUT, IMON to V– Voltage............................. V+ +IN, -IN, IOUT, IMON Current..................................10mA IOUT to IMON Voltage.....................................36V, –0.6V V+, +IN to IOUT Voltage..............................................36V Differential Input Voltage............................................. V+ RSENSE Current (Note 2) Continuous................
PAGE 3
LT6110 Electrical Characteristics The l denotes the specifications which apply over the full specified temperature range, otherwise specifications are at TA = 25°C. V+ = 5V, V– = VIMON = 0V, I+IN = 100µA, VIOUT – VIMON = 1.2V, unless otherwise noted.
PAGE 4
LT6110 Electrical Characteristics 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. In addition to the Absolute Maximum Ratings, the output current and supply current must be limited to insure that the power dissipation in the LT6110 does not allow the die temperature to exceed 150°C.
PAGE 5
LT6110 Typical Performance Characteristics VOS vs VSENSE Voltage 10 V+ = 5V VOS vs IMON Voltage TA = 125°C 200 TA = 85°C 100 TA = 0°C 0 8 TA = –40°C, –55°C –100 TA = 85°C 7 6 5 TA = 125°C 4 3 2 TA = 25°C 1 0.5 0 1.0 1.5 2.0 2.5 VSENSE (V) 3.0 3.5 0 0.1 4.0 3 800 UNITS 100 50 –0.8 –0.4 0 0.4 0.8 IOUT CURRENT ERROR (%) TA = –55°C 1 0 TA = 25°C –1 TA = –40°C –3 1.2 0 –1 TA = 0°C TA = 85°C, 125°C TA = 25°C –2 TA = 85°C, 125°C –4 0.001 0.1 0.
PAGE 6
LT6110 Typical Performance Characteristics IMON Current Error vs Supply Voltage 7 800 UNITS 200 150 100 50 5 4 TA = –55°C 3 TA = 0°C 2 –1 TA = –40°C TA = 25°C 1 TA = 85°C, 125°C 0 0 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.
PAGE 7
LT6110 Typical Performance Characteristics Output Short-Circuit Current vs Temperature 50 OUTPUT SHORT-CIRCUIT CURRENT (mA) 180 160 120 TA = 125°C 100 80 TA = –40°C 60 40 TA = 85°C 20 0 TA = –55°C 0 5 TA = 25°C 40 V+ = 36V 30 20 V+ = 5V 10 TA = 25°C TA = 0°C 0 –200 0 0.5 1 1.5 2 2.5 3 3.5 INPUT VOLTAGE (V) 4 4.5 –5 I+IN = 1mA I+IN = 100µA –10 –15 –20 TA = –40°C T = –55°C A –100 I+IN = 10µA 0 TA = 85°C 100 PSRR vs Frequency 100 V+ = 5V 5 VIOUT = 1.
PAGE 8
LT6110 Typical Performance Characteristics 0µA to 30µA IMON Current Step Response 0µA to 300µA IMON Current Step Response 0µA to 3mA IMON Current Step Response VSENSE VSENSE VSENSE 50mV/DIV 50mV/DIV 50mV/DIV VIOUT VIOUT VIOUT 6110 G34 R+IN = 10k R–IN = 0Ω RIMON = 3.4k TO GND VSENSE = 5mV Step Response VSENSE = 50mV Step Response VSENSE 20mV/DIV VIOUT 50mV/DIV 100µs/DIV V+ = 5V R+IN = 49.9Ω R–IN = 0Ω RIOUT = 1k TO 1.
PAGE 9
LT6110 Pin Functions (TSOT-23/DFN) NC (Pin 1/Pin 8): Not Internally Connected. IOUT (Pin 2/Pin 7): Sinking Current Output. IOUT will sink a current that is equal to VSENSE/RIN. VSENSE is the voltage developed across the sense resisor. IMON (Pin 3/Pin 6): Sourcing Current Output. IMON will source a current that is equal to 3 • VSENSE/RIN. V– (Pin 4/Pin 5): Negative Power Supply. Normally connected to ground. –IN (Pin 5/Pin 4): Negative Input to the Internal Sense Amplifier.
PAGE 10
LT6110 Block Diagram VIN IN OUT + VREG RF REGULATOR I+IN ADJ GND VSENSE ILOAD RWIRE VLOAD+ 0.1µF RIN +IN – V+ RS –IN RSENSE 0.020Ω 1k NC + – IOUT RG IMON V– 6110 F01 RWIRE VLOAD– Figure 1. Block Diagram and Typical Connection 10 6110fa For more information www.linear.
PAGE 11
LT6110 Applications Information INTRODUCTION The LT6110 provides a simple and effective solution to a common problem in power distribution. When a load draws current through a long or thin wire, wire resistance causes an IR drop that reduces the voltage delivered to the load. A regulator IC cannot detect this drop without a Kelvin sense at the load, which requires a multi-conductor wire that is not supported in some applications.
PAGE 12
LT6110 Applications Information +IN and –IN Design Procedure The +IN and –IN inputs can have a maximum differential voltage equal to the supply voltage. This protects the LT6110 if the –IN pin (the remote load side) is accidentally shorted to ground. In this case, the IOUT current must be limited to less than 2mA (see the Limiting the Regulator Boost Voltage section). The design of an LT6110 compensation circuit is a simple 3-step process.
PAGE 13
LT6110 Applications Information Step 2: Determine the resistor on the +IN pin, RIN, required to cancel VDROP. The regulator output voltage will increase as current is pulled from the IOUT pin through the feedback resistor, RF, creating a compensation voltage. VCOMP = IIOUT • RF To cancel the voltage drop at the load, set VCOMP equal to VDROP.
PAGE 14
LT6110 Applications Information Without the compensation circuit (no RSENSE) the load regulation in percent would be, Kelvin Sense Connection to RSENSE To reduce RSENSE error due to trace resistance, the –IN pin and RIN resistor should be connected as close to RSENSE as possible, as reflected in Figure 2. –0.5V LoadRegUNCOMP (%) = • 100 = –10% 5V The regulator’s output will also change due to its own load regulation effects (per the regulator’s specification).
PAGE 15
LT6110 Applications Information In Figure 3 RF is split into RFA and RFB. VREG is the no-load quiescent output voltage of the regulator. The design of these two feedback resistors follows: RFA = VDROP IIOUT IIOUT can be sized to be 100µA at full load current and only this resistor creates the VDROP compensation voltage. RFB = VREG – VFB – RFA IQ IQ is the no-load quiescent current flowing through the resistor string.
PAGE 16
LT6110 Applications Information RWIRE 0.5Ω RIN 200Ω LT3080 IN VIN VLOAD 3V 1A +IN V+ ISET RS –IN LOAD 20mΩ + – VREG LT6110 IOUT + – SET RSET1 301k IMON RSET2 1.69k IMON V– 6110 F05 IMON = 3 IIN+ Figure 5. Wire Loss Compensation Using a Current Referenced LDO To compensate for VDROP at ILOAD(MAX) set: RSET2 = VDROP IIMON and RSET1 = VREG – RSET2 ISET As an example, to compensate this 3V regulator for a 500mV cable drop with a 1A load current set I+IN for 100µA for best accuracy.
PAGE 17
LT6110 Applications Information RWIRE 0.25Ω RSENSE 0.025Ω RIN +IN V+ RS –IN R1= 20mΩ VIN 10µF IN LT1083 ADJ OUT IADJ VREG R1 499Ω IOUT 10µF RG 1k + – R2 = RG = 1.62k ISET R2 3.16k LT6110 IMON VLOAD 12V 5A 1.25V ISET R1• (VLOAD – VREF ) IADJ • R1+ VREF – RG ILOAD • (RSENSE +R WIRE) 3 •I+IN VIMON(MAX) = RG • (ISET +IADJ + 3 •I+IN) V– 6110 F06 IIMON IIMON = 3 I+IN Figure 6.
PAGE 18
LT6110 Applications Information ERROR SOURCES this will create a VDROP of 760mV. Without the LT6110 compensator the regulation of the 5V supply at the load would be 15%. The LT6110 output current allows for reliable compensation for small or large connection wiring voltage drops. The voltage regulation at the remote load can be improved dramatically using the LT6110.
PAGE 19
LT6110 Applications Information To create this current at full load requires an RIN value of VSENSE/IIOUT, 40mV/80µA, or 500Ω. Using the nearest standard 1% tolerance value of 499Ω will be sufficient. Without considering any error terms other than this slight change in value for RIN results in nearly perfect cable drop compensation. The theoretical load regulation would be improved from 15% to less than 0.01%.
PAGE 20
LT6110 Applications Information Table 1. Compensation Error Using Typical Variances Expected at 25°C. FIGURE 7 DESIGN EXAMPLE. TOTAL VDROP TO COMPENSATE = 744mV, I+IN = 74.6µA TERM DESIGN VALUE/SPEC UNITS RSENSE 20 mΩ RIN 499 VOS 0 ∆VOS/∆I+IN 0 COMMENT/CALCULATION FOR MAXIMUM VCOMP FOR MINIMUM VCOMP TYPICAL ERROR VALUE TYPICAL ERROR VALUE 7.50% 21.5 –7.50% 18.5 Ω –0.5% 496.5 0.5% 501.5 µV –100 –100 100 100 –0.15 –0.15 0.15 0.
PAGE 21
LT6110 Applications Information 0dB R+IN –3dB R–IN 1k C1 0 –60 –90 1 IIOUT = 100µA 10 100 FREQUENCY (kHz) PHASE (DEG) –30 +IN V+ RS –IN 20mΩ –120 1000 LT6110 IOUT 6110 F08 + – Figure 8. LT6110 Frequency Response IMON VREG 500mV/DIV V– 6110 F11 Figure 11. LT6110 Frequency Compensation VLOAD 500mV/DIV EXTERNAL CURRENT SENSE RESISTORS 2A 1A 100µs/DIV 6110 F09 Figure 9.
PAGE 22
LT6110 Applications Information The value of the external RSENSE determines the VSENSE voltage. If IIOUT is 100µA then a VSENSE of 50mV is large enough to minimize the compensating IOUT current error due to VOS to less than 1% (see Figure 13). IOUT CURRENT ERROR (%) 100 0.4V ≤ VIOUT ≤ V+ – 1.5V VIMON = V– = 0V VOS(MAX) 10 1 0.1 Precision Current Shunt Resistor A precision, very low VLOAD error, compensation circuit can be implemented with an LT6110 and a precision external RSENSE.
PAGE 23
LT6110 Applications Information Copper Resistor Made from an RF Inductor 24 Table 3. Coilcraft Air Core Inductors for External RSENSE COILCRAFT PART NUMBER INDUCTANCE (nH)* DCR NOMINAL (mΩ) (±6% TYPICAL) IRMS (A) 0908SQ-27N 27 8.5 4.4 2222SQ-221 221 9.8 5 1010 US-141 146 3.1 14 20 PCB TRACE CURRENT (A) An inductor made of copper wire will have a small DC resistance, DCR or RCOIL, with a temperature coefficient that matches that of the copper wire connecting the remote load.
PAGE 24
LT6110 Applications Information 5.4mΩ ±15% AT 25°C PCB RESISTOR 21 2oz COPPER SQUARES TO REGULATOR ONE SQUARE 0.15 INCH × 0.15 INCH TO LOAD A 3/4 CORNER SQUARES 0.15 INCH × 0.15 INCH B A 3.5-SQUARE COLUMN RIN — 3/4 SQUARE 21 SQUARES (6 COLUMNS) — ONE SQUARE –IN — 3/4 SQUARE 6110 F16 V– IMON RS V+ IOUT NC +IN — ONE SQUARE A B Figure 16. LT6110 and PCB Trace Resistor Layout traces at the top and bottom corner squares. There are five connecting traces and their total resistance is 0.
PAGE 25
LT6110 Applications Information Case 1: LT6110 and the wire are at 75°C and the VLOAD error is –0.36%. If the RSENSE temperature coefficient matches the wire’s temperature coefficient of 3900ppm/°C then the VLOAD error is reduced. Using the copper wire resistance of an inductor as an RSENSE external the VLOAD error is reduced to –0.025%. Case 2: The LT6110 is at 75°C, the wire is at 25°C and the VLOAD error is 2.3%. The 2.3% error is mostly due to the internal RSENSE temperature coefficient.
PAGE 26
LT6110 Applications Information temperature then the wire’s resistance vs temperature is: RHIGH = RLOW • (1 + α • (THIGH – TLOW)). An approximation to the temperature rise in a wire due to current can be derived from the wire’s resistance vs temperature equation using the wire’s resistance increase vs safe operating current.
PAGE 27
LT6110 Applications Information ILOAD VREG VIN I+IN SWITCHING REGULATOR FB IOUT ISUPPLY RIN +IN V+ RS SWITCHING REGULATOR IMON RFA FB –IN IIOUT +IN V+ RS VLOAD LOAD –IN 20mΩ RIOUT + – RWIRE VDROP RIN RFB 20mΩ VIOUT IOUT ILOAD VREG VIN + – RG IOUT V– LT6110 IMON V– LT6110 6110 F18 6110 F17 Figure 17. LT6110 Power Dissipation The maximum operating ambient temperature TAMAX is equal to TJMAX – θJA • Power.
PAGE 28
LT6110 Applications Information ILOAD VREG VIN SWITCHING REGULATOR RFA RWIRE VDROP RIN FB +IN V+ RFB RS VLOAD LOAD SWITCHING REGULATOR VZENER IMON – V LT6110 +IN V+ RG IOUT IMON Example: Limit VIOUT to 20V. VLOAD = 48V and ILOADMAX = 2A, RWIRE = 1Ω. RSENSE = 20mΩ, RFA = 20.5k, RFB = 453k, RG = 12.4k, RIN = 402Ω, VFB = 1.223V, IIOUT = 100µA. Calculate VREGMAX = 48 + 2(0.02 + 1) = 50.04V. Calculate VZENERMIN: ⎞ ⎛ ⎜20 + 100 • 10 –6 • ⎟ ⎟ ⎜ ⎟ ⎜ VZENERMIN ≥ 50.04 – ⎜ 20.
PAGE 29
LT6110 Applications Information VIN VREG µModule REGULATOR RINT RSENSE RF + LOAD VLOAD RIN IOUT VFB ILOAD 1/2R WIRE +IN V+ RS – –IN 1/2RWIRE RG + – V– LT6110 6110 F21 Figure 21. An LT6110 with a µModule Regulator 1. ILOADCOMP = 1A. 2. Calculate RIN1 and RIN2: RIN1 = 576Ω and RIN2 = 115k. At ILOAD = 1A VLOAD = 4.75V and at ILOAD = 3.5A VLOAD = 5V.
PAGE 30
LT6110 Applications Information BUCK REGULATOR MODEL VIN – + MODULATOR gm IS THE MODULATOR TRANSCONDUCTANCE SLOPE COMP R OSCILLATOR Q S L LT6110 MODEL VREG CO RFA CCOMP RESR C2 R1 Re C1 + – VREF RFB VFB VLOAD RLOAD RG ERROR AMPLIFIER ge IS THE ERROR AMPLIFIER TRANSCONDUCTANCE RWIRE RSENSE + – VC RIN IIOUT LT6110 6110 F22 Figure 22.
PAGE 31
LT6110 Applications Information produces a load transient that settles without overshoot or ringing (a 10% CCOMP tolerance is adequate). An optional connection for CCOMP is in parallel with RFA and RFB (from VREG to VFB) to reduce the CCOMP value for the smallest capacitor size. Figures 24a through 24c illustrate a typical loop optimization procedure when an LT6110 is included in the regulator’s loop.
PAGE 32
LT6110 Typical Applications LT6110 with External RSENSE and LT3690 Buck Regulator at 3.3V VIN 6.5V TO 25V 10µF VIN EN BST 0.68µF UVLO 4.7µH SS 1000pF VC SW LT3690 0.47µF FB VCCINT SYNC 47pF 100µF PG 22k 680pF 10.2k BIAS 2 301k 0.8V 3 100k GND RT 1 4 32.4k 600kHz NC +IN V+ IOUT LT6110 IMON RS V– –IN 8 RIN 340Ω 7 0.1µF 6 5 RSENSE* 8.5mΩ RWIRE 0.25Ω *THE CURRENT SENSE RESISTOR IS THE DCR OF A LOW COST INDUCTOR. COILCRAFT 0908SQ-27N (27nH) VLOAD LOAD 3.
PAGE 33
LT6110 Typical Applications LT6110 with External PCB RSENSE and LTM4600 µRegulator at 3V VIN 6V TO 24V + 150µF 22µF 22µF VIN VREG VOUT 22µF 100µF 100µF LTM4600HV 1M RUN/SS 0.1µF FCB SGND PGND 100k ±0.5% 0.6V VOSET 1000pF RF 18.7k RG 3.92k 1 2 3 4 NC +IN IOUT V+ LT6110 IMON RS V– –IN 8 RIN 523Ω 7 0.1µF 6 5 PCB RSENSE RWIRE 6mΩ 0.075Ω ±20% + RWIRE 0.075Ω WIRE DROP COMPENSATION: VLOAD = 3.0V, ILOADMAX = 10A, USING 20ft, 18AWG WIRE WITH GROUND RETURN.
PAGE 34
LT6110 Typical Applications LT6110 with External RSENSE and LTC3789 Buck-Boost Regulator at 12V VIN 5V TO 36V INTVCC 100k 1 2 1nF 0.01µF 0.01µF 3 4 14.7k 5 6 7 121k 8 400kHz VIN VREG 9 10 11 12 13 PGOOD VFB SW1 TG1 SS BOOST1 SENSE+ PGND SENSE– BG1 ITH SGND LTC3789 VIN MODE/PLLIN INTVCC FREQ EXTVCC RUN VINSNS VOUTSNS BG2 BOOST2 27 2.2µF 14 I – OSENSE TG2 SW2 TRIM + 270µF 390pF 5.6Ω 10Ω 26 QA Si7848BDP 25 24 DA DFLS160 23 1µF 22 L 4.
PAGE 35
LT6110 Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. TS8 Package 8-Lead Plastic TSOT-23 (Reference LTC DWG # 05-08-1637 Rev A) 0.40 MAX 2.90 BSC (NOTE 4) 0.65 REF 1.22 REF 1.4 MIN 3.85 MAX 2.62 REF 2.80 BSC 1.50 – 1.75 (NOTE 4) PIN ONE ID RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR 0.22 – 0.36 8 PLCS (NOTE 3) 0.65 BSC 0.80 – 0.90 0.20 BSC 0.01 – 0.10 1.00 MAX DATUM ‘A’ 0.30 – 0.50 REF 0.09 – 0.20 (NOTE 3) 1.
PAGE 36
LT6110 Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. DC8 Package 8-Lead Plastic DFN (2mm × 2mm) (Reference LTC DWG # 05-08-1719 Rev A) 0.70 ±0.05 2.55 ±0.05 1.15 ±0.05 0.64 ±0.05 (2 SIDES) PACKAGE OUTLINE 0.25 ±0.05 0.45 BSC 1.37 ±0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED R = 0.05 TYP 2.00 ±0.10 (4 SIDES) PIN 1 BAR TOP MARK (SEE NOTE 6) R = 0.115 TYP 5 8 0.40 ±0.
PAGE 37
LT6110 Revision History REV DATE DESCRIPTION A 11/13 Maximum Amplifier Bias Current changed from 200nA to 100nA PAGE NUMBER 3 Addition of Minimum Input Voltage graph 7 Edits to Compensating an Output Referred Adjustable Voltage Regulator section 16 Edits to Error Sources section 18, 19, 20 Title added – Wire Drop Compensation Using a Micromodule Regulator 29 Edits to schematic LT6110 with External PCB RSENSE and LTM4600 µModule Regulator at 3V 33 Replaced schematic LT6110 with External PCB
PAGE 38
LT6110 Typical Application LT6110 with Internal RSENSE and LT3975 Buck Regulator at 3.3V VIN 7V TO 42V 100µF B00ST VIN 10µF 0.47µF EN 4.7µH SW PDS360 LT3975 VREG OUT 100µF SS 10nF RT 78.7k f = 600kHz SYNC GND FB 1.197V 1µF 16.5k 10pF 1M 1 2 3 576k 4 NC +IN V+ IOUT LT6110 IMON RS V– –IN 8 RIN 499Ω 7 0.1µF RWIRE 0.32Ω 6 5 + WIRE DROP COMPENSATION: VLOAD = 3.3V, ILOADMAX = 2.5A, USING 6ft, 30AWG WIRE WITH GROUND RETURN. MEASURED VLOAD REGULATION FOR 0 ≤ ILOAD ≤ 2.