MB3825A Ver la hoja de datos (PDF) - Fujitsu

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MB3825A

6-ch DC/DC Converter IC With Synchronous Rectifier

Fujitsu 

MB3825A

3. Protective Functions

(1) Timer-latch short-circuit protection circuit

The short detection comparator in each channel detects the output voltage level, and when any channel output

voltage falls below the short detection voltage, or the SCP terminal (pin 13) voltage falls below the reference

voltage, the timer circuit starts operating and the capacitor CSCP connected to the CSCP terminal (pin 23) starts

charging.

When the capacitor charge reaches approximately 0.7 V, the output transistor is turned off and the idle interval

becomes 100%.

When actuated, this protection circuit can be reset by turning on the power supply again. (See “METHOD OF

SETTING TIME CONSTANT FOR TIMER-LATCH SHORT PROTECTION CIRCUIT”.)

(2) Under voltage lockout protection circuit

A transient state at power-on or a momentary drop of the power supply voltage causes the control IC to mal-

function, resulting in system breakdown or system deterioration. By detecting the internal reference voltage with

respect to the power supply voltage, this protection circuit resets the latch circuit to turn off the output transistor

and set the duty (OFF) = 100%, while at the same time holding the CSCP terminal (pin 23) at the “L”. The reset

is cleared when the power supply voltage becomes greater than or equal to the threshold voltage level of this

protection circuit.

(3) Output Supply Monitor Comparator (Vcc Comp.)

The output supply monitor comparator compares the output circuit power supply (VCC (O) 1, 3, VCC (O) 2, VCC

(O) 4, 5, 6) to the VCC level, and operates the timer-latch short protection circuit if any of the output circuit power

supplies fall below Vcc − 0.65 V.

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