Datasheet

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LTC4350

4350fb

Typical applicaTion

FeaTures DescripTion

Hot Swappable

Load Share Controller

The LTC

4350 is a load share controller that allows sys-

tems to equally load multiple power supplies connected

in parallel. The output voltage of each supply is adjusted

using the SENSE

input until all currents match the share

bus. The LTC4350 also isolates supply failures by turning

off the series pass transistors and identifying the failed

supply. The failed supply can then be removed and replaced

with a new unit without turning off the system power. The

LTC4350 is available in a 16-pin narrow SSOP package.

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and Hot

Swap and ThinSOT are trademarks of Linear Technology Corporation. All other trademarks are

the property of their respective owners.

5V Load Share (5A per Module)

applicaTions

Build N + 1 Redundant Supply

Hot Swap™ Power Supplies

Isolates Supply Failures from Output

Eliminates ORing Diodes

Identifies and Localizes Output Low, Output High

and Open-Circuit Faults

Output Voltages from 1.5V to 12V

16-Lead Narrow SSOP Package

Servers and Network Equipment

Telecom and Base Station Equipment

Distributed Power Systems

GAIN COMP1 GND COMP2

GATE

0.010Ω

SUD50N03-07

–

SET

OUT

STATUS STATUS

SHARE BUS

TIMER

OUT

–

0.1µF

51Ω 100Ω

37.4k

12.1k

100Ω

4.7µF

1000pF

150Ω

0.1µF

LTC4350

0.1µF

34k

470k

12.1k

121k

43.2k

274k

0.1µF

VICOR*

VI-J30-CY

SENSE

OUT

SENSE

–

TRIM

OUT

–

GAIN COMP1 GND COMP2

GATE

0.010Ω

SUD50N03-07

–

SET

OUT

STATUS STATUS

TIMER

0.1µF

51Ω 100Ω

37.4k

12.1k

100Ω

4350 TA01

4.7µF

1000pF

150Ω

0.1µF

LTC4350

34k

*LOAD SHARING CIRCUIT WORKS WITH MOST POWER SUPPLIES THAT HAVE A SENSE

OR FB PIN

470k

0.1µF

VICOR*

VI-J30-CY

SENSE

OUT

SENSE

–

TRIM

OUT

–

0.1µF

12.1k121k

43.2k

274k

NOT RECOMMENDED FOR NEW DESIGNS

Contact Linear Technology for Potential Replacement

Summary of content (18 pages)

PAGE 1
LTC4350 Hot Swappable Load Share Controller NOT RECOMMENDED FOR NEW DESIGNS Contact Linear Technology for Potential Replacement Features n n n n n n n Description Build N + 1 Redundant Supply Hot Swap™ Power Supplies Isolates Supply Failures from Output Eliminates ORing Diodes Identifies and Localizes Output Low, Output High and Open-Circuit Faults Output Voltages from 1.
PAGE 2
LTC4350 Absolute Maximum Ratings Pin Configuration (Note 1) TOP VIEW Supply Voltage (VCC).................................................17V Input Voltage TIMER.................................................... –0.3V to 1.2V R+, R– (Note 2)....................................... –0.3V to 17V FB.......................................................... –0.3V to 5.3V OV, UV........................................................ –0.3V to 17V Output Voltage COMP1..........................................
PAGE 3
LTC4350 Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 5V unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS DC Characteristics VUVTH UV Pin Threshold High Going Threshold Low Going Threshold l l 1.215 1.205 1.244 1.220 1.258 1.237 V V VOVTH OV Pin Threshold High Going Threshold Low Going Threshold l l 1.203 1.180 1.220 1.205 1.250 1.
PAGE 4
LTC4350 Typical Performance Characteristics ICC vs VCC 3.5 ICC vs Temperature 1.66 TA = 25°C VCC = 5V UV THRESHOLD (V) 1.62 ICC (mA) 2.5 2.0 1.60 1.58 1.5 1.56 0 2 4 8 6 VCC (V) 10 12 1.54 –50 14 UV Threshold vs Temperature 1.222 VCC = 5V 1.250 OV THRESHOLD (V) 1.235 1.230 1.225 0 2 4 8 6 VCC (V) 10 12 14 4350 G03 OV Threshold vs Temperature 1.225 TA = 25°C VCC = 5V 1.220 1.216 1.214 1.212 1.210 1.208 1.215 1.210 1.205 0 25 50 TEMPERATURE (°C) –25 75 1.
PAGE 5
LTC4350 Typical Performance Characteristics Gain Pin Voltage vs Temperature 2.7 2.6 ∆VGATE vs VCC 13 RGAIN = 25k (VR+ – VR–) = 100mV VCC = 5V ∆VGATE vs Temperature 13.0 TA = 25°C VCC = 5V 12 12.5 2.4 ∆VGATE (V) 2.5 ∆VGATE (V) GAIN (V) 11 10 12.0 9 8 2.3 2.2 –50 11.5 7 –25 0 25 50 TEMPERATURE (°C) 75 100 6 0 2 4 4350 G10 8 6 VCC (V) 10 12 14 4350 G11 11.0 –50 –25 0 25 50 TEMPERATURE (°C) 75 100 4350 G12 Pin Functions UV (Pin 1): Undervoltage Pin.
PAGE 6
LTC4350 Pin Functions GND (Pin 8): Chip Ground. FB (Pin 9): Analog Error Amplifier Input (E/A1). This pin is used to monitor the output supply voltage with an external resistive divider. The FB pin voltage is compared to 1.220V reference. The difference between the FB pin voltage and the reference is amplified and output on the COMP1 pin. RSET (Pin 10): Analog Output Pin. The IOUT amplifier converts the voltage at the COMP2 pin (down a diode voltage) to the RSET pin.
PAGE 7
LTC4350 Block Diagram 14 13 R+ GATE + VCC 12 R– – 16 CHARGE PUMP ISENSE gm = 1m 6 Ω COMP1 GAIN + REF 9 SB E/A1 FB – COMP2 E/A2 – REVERSE CURRENT R IOUT + – UV – OV + 2µA/6µA + LOGIC REF 10 – REF 2 11 IOUT + +– RSET 1 5 OVER/UNDER CURRENT 30mV – 7 20k + R+ 4 – TIMER STATUS 3 15 GND 8 4350 BD 4350fb
PAGE 8
LTC4350 Applications Information Introduction Many system designers find it economically feasible to parallel power supplies to achieve redundancy. The second trend is providing some load sharing between the many supplies. In some cases, a failure in any one supply will trigger a sequence that disconnects the faulty supply and sends a flag to the system. Then, a service technician will swap in a good supply.
PAGE 9
LTC4350 Applications Information OUT+ PASS-FET USED TO DISCONNECT A BAD POWER SUPPLY AND TO HOT-SWAP A POWER SUPPLY R 1 SENSE 2 CG + – THIS VOLTAGE REPRESENTS THE REFERENCE CURRENT VALUE (i.e., SHARE BUS) NEEDED TO FORCE THE OUTPUT VOLTAGE TO EQUAL THE REF FB PIN ISENSE GATE DRIVE ROUT + IADJ LOAD 4 3 – SENSE+ gm = 1m Ω IOUT PIN COMP1 PIN – SHARE BUS E/A1 REF THIS RESISTOR CONVERTS IADJ TO A VOLTAGE TO MODIFY THE REMOTE SENSE INPUT OF THE POWER SUPPLY (SENSE+).
PAGE 10
LTC4350 Applications Information increases. The output voltage will then increase by an amount equal to the voltage drop across ROUT. The external resistor, RSET, sets the voltage to current relationship in the IOUT block. The current in ROUT is defined as IADJ = (VCOMP2 – 0.58V)/RSET. The maximum voltage that can be applied across RSET is 1V. The range of the output voltage adjustment is set to be VMAXADJ = ROUT /RSET. This sets the worst-case output voltage if the share bus is accidentally shorted to VCC.
PAGE 11
LTC4350 Applications Information A timer is started as soon as the OV pin exceeds 1.220V. The timer consists of a 6µA current source into an external capacitor on the TIMER pin. As soon as the voltage on the TIMER pin exceeds 1.220V, the STATUS pin is pulled low. There are two external power FETs in Figure 3. The FET with its drain on the power supply side (left) and its source on the load side (right) is used to block high voltage faults from the load.
PAGE 12
LTC4350 Applications Information a SENSE+ line is not available, then the feedback divider at the module’s error amplifier can be used. The next step is to determine the maximum positive adjustment needed for each power supply. This adjustment includes any I • R drops across sense resistors, power FETs, wiring and connectors in the supply path between the power supply and the load. For example, if the maximum current is 10A and the parasitic resistance between the power supply and load is 0.
PAGE 13
LTC4350 Applications Information If we set RSET to be 100Ω, then an ROUT of 100Ω allows the output voltage a full 1V adjustment. For the 0.3V range in this example, the ROUT is 30Ω. In some power modules, there already exists a resistor between the SENSE + line and the power output. In this case, the value of ROUT is the parallel combination of two resistors, one in the module and one placed between the SENSE+ and output terminals of the module.
PAGE 14
LTC4350 Applications Information compensation capacitor CP2 can be looked up in Table 1 using tR. The value for the zero setting resistor, RP1, is 150Ω. This value guarantees the zero is at or above the crossover frequency. Table 1 power supply, then the LTC4350 will reside with the power supply on a daughter card that plugs into the main board. In this case, the input and output capacitors need to be hot swapped (see Figure 7). The output capacitors are Hot Swap protected by the LTC4350.
PAGE 15
LTC4350 Applications Information –48V RTN –48V RTN POWER SUPPLY 1 RTN VIN+ VDD UV LT4250L OV VEE SENSE PWRGD 1 OUT+ 3.3V 2 4 3 ON/OFF DRAIN GATE RSENSE ROUT SENSE+ SENSE– RG –48V 3 1 –48V –48V 3.3VOUT 4 2 VIN– OUT– CG VCC GND RSET SB RGAIN STATUS IOUT RSET R+ R– FB STATUS GAIN SB LTC4350 GND CONNECTOR GATE TIMER CT UV OV CUV COMP1 COMP2 LOAD CP1 CP2 RP2 –48V RTN POWER SUPPLY 2 RTN VIN+ VDD UV LT4250L OV VEE SENSE PWRGD 1 OUT+ 3 3.
PAGE 16
LTC4350 Package Description GN Package 16-Lead Plastic SSOP (Narrow .150 Inch) (Reference LTC DWG # 05-08-1641) .189 – .196* (4.801 – 4.978) .045 ±.005 16 15 14 13 12 11 10 9 .254 MIN .009 (0.229) REF .150 – .165 .229 – .244 (5.817 – 6.198) .0165 ± .0015 .150 – .157** (3.810 – 3.988) .0250 BSC RECOMMENDED SOLDER PAD LAYOUT 1 .015 ± .004 × 45° (0.38 ± 0.10) .007 – .0098 (0.178 – 0.249) .0532 – .0688 (1.35 – 1.75) 2 3 4 5 6 7 8 .004 – .0098 (0.102 – 0.249) 0° – 8° TYP .016 – .050 (0.406 – 1.
PAGE 17
LTC4350 Revision History (Revision history begins at Rev B) REV DATE DESCRIPTION PAGE NUMBER B 3/10 Not Recommended for New Designs 1 4350fb 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.
PAGE 18
LTC4350 Applications Information 24VIN VIN 24V VIN CIN RSENSE 1.5V RSENSE 1.5V COUT RG GND GND VCC SENSE GATE ON LT1641 TIMER INTVCC GND CG ROUT LTC1629 VOS+ VCC RSET RGAIN 1.