RR0816P-154-D Просмотр технического описания (PDF) - Fujitsu

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RR0816P-154-D

2-ch DC/DC Converter IC with Overcurrent Protection

Fujitsu 

MB39A104

■ SETTING THE SOFT-START AND DISCHARGE TIMES

To prevent rush currents when the IC is turned on, you can set a soft-start by connecting soft-start capacitors

(CS1 and CS2) to the CS1 terminal (pin 11) for channel 1 and the CS2 terminal (pin 14) for channel 2, respectively.

When CTL terminal (pin 24) goes to “H” level and IC starts (VCC ≥ UVLO threshold voltage), the external soft-

start capacitors (CS1 and CS2) connected to CS1 and CS2 terminals are charged at 10 µA. The error amplifier

output (FB1 (pin 9) , FB2 (pin 16) ) is determined by comparison between the lower one of the potentials at two

non-inverted input terminals (1.24 V, CS1 terminal voltages) and the inverted input terminal voltage (−INE1 (pin

10) voltage, −INE2 (pin 15) voltage).

The FB1 (FB2) terminal voltage is decided for the soft-start period by the comparison between 1.24 V in an

internal reference voltage and the voltages of the CS1 (CS2) terminal. The DC/DC converter output voltage

rises in proportion to the CS1 (CS2) terminal voltage as the soft-start capacitor connected to the CS1 (CS2)

terminal is charged.

The soft-start time is obtained from the following formula:

Soft-start time: ts (time to output 100%)

ts (s) =: 0.124 × CS (µF)

=: 5 V

CS1 (CS2) terminal voltage

=: 1.24 V

=: 0 V

Error Amp block −INE1 (−INE2) voltage

t

Soft-start time (ts)

14

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