Texas Instruments UC3902N, UC3902DTR, UC3902D, UC2902N, UC2902DTR Datasheet
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Load Share Controller
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
UC1902
UC2902
UC3902
PRELIMINARY
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.
BLOCK DIAGRAM
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LOAD SHARE CONTROLLER |
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GND |
1 |
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8 |
VCC |
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BIAS |
UVLO |
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– |
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SHARE DRIVE AMPLIFIER |
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40R |
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+ |
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R |
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SENSE |
2 |
– |
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7 |
SHARE+ |
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+ |
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+ |
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CURRENT SENSE |
SHARE SENSE AMPLIFIER |
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AMPLIFIER |
– |
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6 |
SHARE– |
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+ |
ERROR AMPLIFIER |
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ADJ |
3 |
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35mV |
+ |
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ADJ AMPLIFIER |
0.6V |
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– |
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+ |
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5 |
COMP |
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+ |
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– |
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2.3V |
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ADJR |
4 |
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UDG-99042 |
SLUS232 - FEBRUARY 1999 |
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ABSOLUTE MAXIMUM RATINGS
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.
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, VADJ = 5V, COMP = 5nF capacitor to GND, VSHARE– = 0V, TA = TJ.
PARAMETERS |
TEST CONDITIONS |
MIN |
TYP |
MAX |
UNIT |
Power Supply |
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Supply Current |
SHARE+ = 1V, SENSE = 0V |
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4 |
6 |
mA |
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VCC = 20V |
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6 |
10 |
mA |
Undervoltage Lockout |
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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 |
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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 |
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0.6 |
1 |
1.5 |
kΩ |
Share Drive Amplifier |
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SHARE+ High |
VCC = 2.5V, SENSE = –50mV, ISHARE+ = –1mA |
1.2 |
1.4 |
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V |
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VCC = 12V, SENSE = –250mV, ISHARE+ = –1mA |
9.6 |
10 |
10.4 |
V |
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VCC = 20V, SENSE = –250mV, ISHARE+ = –1mA |
9.6 |
10 |
10.4 |
V |
SHARE+ Low |
VCC = 2.5V, SENSE = +10mV, ISHARE+ = –1mA |
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20 |
50 |
mV |
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VCC = 12V, SENSE = +10mV, ISHARE+ = –1mA |
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20 |
50 |
mV |
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VCC = 20V, SENSE = +10mV, ISHARE+ = –1mA |
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20 |
50 |
mV |
SHARE+ Output Voltage |
Measures SHARE+, SENSE = 0mV, RSHARE+ = 200Ω resistor |
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20 |
40 |
mV |
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SHARE+ to GND |
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CMRR |
0 ≤ SHARE– ≤ 1V , SENSE used as input to amplifier |
50 |
90 |
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dB |
Load Regulation |
Load on SHARE+, –1mA ≤ ILOAD ≤ –20mA, SENSE = |
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0 |
20 |
mV |
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–25mV |
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Short Circuit Current |
SHARE+ = 0V, SENSE = –25mV |
–85 |
–50 |
–20 |
mA |
Slew Rate |
SENSE = +10mV to –90mV Step, 200Ω resistor SHARE+ to |
0.16 |
0.27 |
0.37 |
V/μs |
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GND |
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SENSE = –90mV to +10mV Step, 200Ω resistor SHARE+ to |
0.12 |
0.24 |
0.34 |
V/μs |
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GND |
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2
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