feature

2.7-V to 20-V operation

pin package

Requires minimal number of external components

Compatible with existing power supply designs that include remote outputs

Voltage sensor

Differential Shared Bus

Precision Current Sense Amplifier (Gain of 40)

Undervoltage lockout circuit

User Programmable Shared Loop Compensation

application

Parallel power supply

illustrate

The UC3902 load sharing controller is an 8-pin device that balances the current drawn from independent parallel power supplies. Load sharing is accomplished by adjusting the output current of each power supply to a level proportional to the voltage on the shared bus.

The main supply is automatically designated as the supply regulated to the highest voltage, driving the shared bus at a voltage proportional to its output current. The UC3902 trims the output voltages of the other parallel power supplies so that they each support their share of the load current. Typically, each power supply is designed for the same current level, although this is not required for use with the UC3902. By properly adjusting the current sense resistors, power supplies with different output current capabilities can be paralleled with each power supply that provides the same percentage of output current capability for a particular load.

application information

The values of the five passive components must be determined to configure the UC3902 load sharing controller. The output and return lines of each converter are connected together at the load, and a current sense resistor RSENSE is inserted into each negative return line. Another resistor, R, is also inserted into each positive sense line. The differential shared bus terminals (shared+ and shared-) of each UC3902 are connected together separately, and the shared node is also connected to system ground. A typical application is shown in Figure 1. adjuvant disease

The design of a load sharing controller can be performed in the following steps:

first step.

When A is 40, the gain of the current sense amplifier CSA is at full load and the voltage drop across the R resistor is I × R. Taking into account the gain of the current sense amplifier, the voltage at full load on the current sharing bus, the sense O(max) sense

The voltage must remain at 1.5 volts below VCC or below 10 volts, whichever is less. VSHARE represents an upper limit, but designers should choose a full-scale shared bus voltage, keeping in mind that every volt on the load-sharing bus adds approximately 100 mA to the master controller's supply current, proportional to the number of parallel slave units times.

Step two.

Care must be taken to ensure that I is low enough so that both drive current and power dissipation are within the capabilities of the device. For most applications, I currents between 5-10 mA are acceptable. In a typical application, a 360ΩRG resistor from the ADJR pin to ground sets IADJ (max) to approximately 5mA. Adjust (max) Adjust (max)

R must be low enough not to interfere with the proper operation of the converter's voltage feedback loop. Typical R values are between 20Ω and 100Ω, depending on V, V and the selected I value. Adjuvant Disease Adjuvant Disease O (max) Adjusted (max)

the fourth step.

A resistor in series with C is required to improve the phase margin of the load sharing loop. The zero point is at the load sharing loop crossover frequency f. Class C Class C When the system is powered on, the converter with the highest output voltage tends to provide the most current and control the shared bus. The other converters increase their output voltages until their output currents are proportional to the shared bus voltage minus 50 mV. The converter as the main circuit may vary due to differences in warm-up drift, load and line transient response of each converter.

Additional Information

one. Application Note U-163, (Technical Information Literature Number: SLUA128) Laszlo Balogh's UC3902 Load Sharing Controller and Its Performance in Distributed Power Systems Tape and Reel Information

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