Texas Instruments UC3902N, UC3902DTR, UC3902D, UC2902N, UC2902DTR Datasheet

UC1902
UC2902
UC3902

PRELIMINARY

SLUS232 - FEBRUARY 1999

FEATURES

• 2.7V to 20V Operation

• 8-Pin Package

• Requires Minimum Number of

External Components

• Compatible with Existing Power
Supply Designs Incorporating Remote
Output Voltage Sensing

• Differential Share Bus

• Precision Current Sense Amplifier with

Gain of 40

• UVLO (Undervoltage Lockout)
Circuitry

• User Programmable Share Loop
Compensation

Load Share Controller

1

3

2

4

8

6

7

5

+

–

R

40R

LOAD SHARECONTROLLER

+

–

ADJ AMPLIFIER

BIAS UVLO

+

–

+

–

+

–

SHARE SENSE AMPLIFIER

SHARE DRIVE AMPLIFIER

2.3V

35mV

+

0.6V
+

CURRENT SENSE
AMPLIFIER

ERROR AMPLIFIER

GND

SENSE

ADJ

ADJR

VCC

SHARE+

SHARE–

COMP

BLOCK DIAGRAM

UDG-99042

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 supply’s 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.

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 20Ω – 100Ω) to be inserted.

2

UC1902
UC2902
UC3902

CONNECTION DIAGRAM

DIL-8, SOIC-8 (Top View)
N, J and D Package

ELECTRICAL CHARACTERISTICS:

Unless otherwise specified, TA= –55°C to +125°C for UC1902, –40°C to+85°C for

UC2902, 0°C to 70°C for UC3902, VCC = 5V, R

ADJR

= 1kΩ, V

ADJ

= 5V, COMP = 5nF capacitor to GND, V

SHARE

–

= 0V, TA= TJ.

PARAMETERS TEST CONDITIONS MIN TYP MAX UNIT

Power Supply

Supply Current SHARE+ = 1V, SENSE = 0V 4 6 mA

VCC = 20V 6 10 mA

Undervoltage Lockout

Startup Voltage SHARE+ = 0.2V, SENSE = 0V, COMP = 1V 2.3 2.5 2.7 V
Hysteresis SHARE+ = 0.2V, SENSE = 0V, COMP = 1V 60 100 140 mV

Current Sense Amplifier

Input Offset Voltage 0.1V ≤ SHARE+ ≤ 1.1V –2.5 –0.5 1.5 mV
Gain SENSE to SHARE 0.1V ≤ SHARE+ ≤ 1.1V –41 –40 -39 V/V
Input Resistance 0.6 1 1.5 kΩ

Share Drive Amplifier

SHARE+ High VCC = 2.5V, SENSE = –50mV, I

SHARE+ = –1mA 1.2 1.4 V

VCC = 12V, SENSE = –250mV, I

SHARE+ = –1mA 9.6 10 10.4 V

VCC = 20V, SENSE = –250mV, I

SHARE+ = –1mA 9.6 10 10.4 V

SHARE+ Low VCC = 2.5V, SENSE = +10mV, I

SHARE+ = –1mA 20 50 mV

VCC = 12V, SENSE = +10mV, I

SHARE+ = –1mA 20 50 mV

VCC = 20V, SENSE = +10mV, I

SHARE+ = –1mA 20 50 mV

SHARE+ Output Voltage Measures SHARE+, SENSE = 0mV, R

SHARE+ = 200Ω resistor

SHARE+ to GND

20 40 mV

CMRR 0 ≤ SHARE– ≤ 1V , SENSE used as input to amplifier 50 90 dB
Load Regulation Load on SHARE+, –1mA ≤ I

LOAD ≤ –20mA, SENSE =

–25mV

020mV

Short Circuit Current SHARE+ = 0V, SENSE = –25mV –85 –50 –20 mA
Slew Rate SENSE = +10mV to –90mV Step, 200Ω resistor SHARE+ to

GND

0.16 0.27 0.37 V/µs

SENSE = –90mV to +10mV Step, 200Ω resistor SHARE+ to
GND

0.12 0.24 0.34 V/µs

Supply Voltage (ADJ and VCC) . . . . . . . . . . . . . . –0.3V to 20V

SENSE Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . –5V to +5V

ADJR, COMP Voltage. . . . . . . . . . . . . . . . . . . . . . –0.3V to +4V

SHARE–, SHARE+ Voltages . . . . . . . . . . . . . . . . –0.3V to 10V

SHARE+ Current . . . . . . . . . . . . . . . . . . . . . –100mA to +10mA

ADJ Current . . . . . . . . . . . . . . . . . . . . . . . . . . . –1mA to +30mA

Storage Temperature . . . . . . . . . . . . . . . . . . . –65°C to +150°C

Junction Temperature. . . . . . . . . . . . . . . . . . . –55°C to +150°C

Lead Temperature (Soldering, 10sec.) . . . . . . . . . . . . . +300°C

All voltages are with respect to pin 1. Currents are positive into,
negative out of the specified terminal. Consult Packaging Sec­tion of the Databook for thermal limitations and considerations
of packages.

ABSOLUTE MAXIMUM RATINGS