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UC2902

UC3902

SLUS232E − DECEMBER 19, 2002 − REVISED JULY 2011

LOAD SHARE CONTROLLER

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FEATURES

2.7-V to 20-V Operation

D 8-Pin Package

D Requires Minimum Number of External

Components

D Compatible with Existing Power Supply

Designs Incorporating Remote Output

Voltage Sensin

D Differential Share Bus

D Precision Current Sense Amplifier (40 Gain)

D UVLO (Undervoltage Lockout) Circuitry

D User Programmable Share Loop

Compensation

APPLICATIONS

Paralelled Power Supplies

DESCRIPTION

The UC3902 load share controller is an 8-pin

device that balances the current drawn from

independent, paralleled power supplies. Load

sharing is accomplished by adjusting each

supplies’ output current to a level proportional to

the voltage on a share bus.

The master power supply, which is automatically

designated as the supply that regulates to the

highest voltage, drives the share bus with a

voltage proportional to its output current. The

UC3902 trims the output voltage of the other

paralleled supplies so that they each support their

share of the load current. Typically, each supply is

designed for the same current level although that

is not necessary for use with the UC3902. By

appropriately scaling the current sense resistor,

supplies with different output current capability

can be paralleled with each supply providing the

same percentage of their output current capability

for a particular load.

UDG−01141

−

40R

−

ADJ AMPLIFIER

BIAS UVLO

−

SHARE SENSE AMPLIFIER

SHARE DRIVE AMPLIFIER

2.3 V

35 mV

0.6 V

CURRENT SENSE

AMPLIFIER

ERROR AMPLIFIER

GND

SENSE

ADJ

ADJR

VCC

SHARE+

SHARE−

COMP

PRODUCTION DATA information is current as of publication date.

Products conform to specifications per the terms of Texas Instruments

standard warranty. Production processing does not necessarily include

testing of all parameters.

Summary of content (10 pages)

PAGE 1
UC2902 UC3902 SLUS232E − DECEMBER 19, 2002 − REVISED JULY 2011 LOAD SHARE CONTROLLER FEATURES D 2.7-V to 20-V Operation D 8-Pin Package D Requires Minimum Number of External D D D D D DESCRIPTION The UC3902 load share controller is an 8-pin device that balances the current drawn from independent, paralleled power supplies. Load sharing is accomplished by adjusting each supplies’ output current to a level proportional to the voltage on a share bus.
PAGE 2
UC2902 UC3902 SLUS232E − DECEMBER 19, 2002 − REVISED JULY 2011 DESCRIPTION (continued) A differential line is used for the share bus to maximize noise immunity and accommodate different voltage drops in each power converter’s ground return line. Trimming of each converter’s output voltage is accomplished by injecting a small current into the output voltage sense line, which requires a small resistance (typically 20 Ω to 100 Ω) to be inserted. These devices have limited built-in ESD protection.
PAGE 3
UC2902 UC3902 SLUS232E − DECEMBER 19, 2002 − REVISED JULY 2011 ELECTRICAL CHARACTERISTICS TJ = –40°C to 105°C, (unless otherwise noted) TEST CONDITIONS PARAMETER MIN TYP MAX UNIT Power SUPPLY SUPPLY CURRENT ICC Supply current SHARE+ = 1 V, SENSE = 0 V VCC = 20 V 4 6 6 10 mA UNDERVOLTAGE LOCKOUT VCC Startup voltage SHARE+ = 0.2 V, SENSE = 0 V, COMP = 1 V 2.3 2.5 2.7 V Hysteresis SHARE+ = 0.
PAGE 4
UC2902 UC3902 SLUS232E − DECEMBER 19, 2002 − REVISED JULY 2011 ELECTRICAL CHARACTERISTICS (continued) TJ = –40°C to 105°C, (unless otherwise noted) PARAMETER TEST CONDITIONS MIN TYP 8 15 8 15 MAX UNIT SHARE SENSE AMPLIFIER RIN Input impedance V(SHARE+) = 1 V, V(SENSE) = 10 mV V(SHARE−) = GND R(SHARE+) = 200 Ω (SHARE+ to GND) V(SHARE−) = 1 V, V(SENSE) = 10 mV kΩ V(SHARE) Threshold voltage V(SENSE) = 0 V 41 70 CMRR Common mode rejection ratio 0 V ≤ V(SHARE−) ≤ 1 V, V(SENSE) = −2.
PAGE 5
UC2902 UC3902 SLUS232E − DECEMBER 19, 2002 − REVISED JULY 2011 ORDERING INFORMATION TA 40°C to 85°C −40°C 0°C to 70°C (2) PACKAGE(2) PART NUMBER SOIC (D) UC2902D Plastic DIP (N) UC2902N SOIC (D) UC3902D Plastic DIP (N) UC3902N The D package is also available taped and reeled. Add an R suffix to the device type (i.e., bq24901DR) for quantities of 3,000 devices per reel.
PAGE 6
UC2902 UC3902 SLUS232E − DECEMBER 19, 2002 − REVISED JULY 2011 APPLICATION INFORMATION The values of five passive components must be determined to configure the UC3902 load share controller. The output and return lines of each converter are connected together at the load, with current sense resistor RSENSE inserted in each negative return line. Another resistor, RADJ, is also inserted in each positive remote sense line.
PAGE 7
UC2902 UC3902 SLUS232E − DECEMBER 19, 2002 − REVISED JULY 2011 The share loop compensation capacitor, CC is calculated to produce the desired share loop unity gain crossover frequency, fC. The share loop error amplifier’s transconductance, gM is nominally 4.5 ms. The values of the resistors are already known. Typically, fC is set to at least one order of magnitude below the converter’s closed loop bandwidth.
PAGE 8
PACKAGE MATERIALS INFORMATION www.ti.com 28-Jul-2011 TAPE AND REEL INFORMATION *All dimensions are nominal Device Package Package Pins Type Drawing SPQ Reel Reel A0 Diameter Width (mm) (mm) W1 (mm) B0 (mm) K0 (mm) P1 (mm) W Pin1 (mm) Quadrant UC2902DTR SOIC D 8 2500 330.0 12.4 6.4 5.2 2.1 8.0 12.0 Q1 UC3902DTR SOIC D 8 2500 330.0 12.4 6.4 5.2 2.1 8.0 12.
PAGE 9
PACKAGE MATERIALS INFORMATION www.ti.com 28-Jul-2011 *All dimensions are nominal Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm) UC2902DTR SOIC D 8 2500 340.5 338.1 20.6 UC3902DTR SOIC D 8 2500 340.5 338.1 20.
PAGE 10
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