Fujitsu MB39A104 manual Control Function, Protective Functions, Operating circuit, OUT1, OUT2

MB39A104

2. Control Function

When CTL terminal (pin 24) is “L” level, IC becomes the standby mode. The power supply current is 10 ∝A (Max) at the standby mode.

On/Off Setting Conditions

CTL

L

H

Power

OFF (Standby)

ON (Operating)

3.Protective Functions

(1)Timer-latch overcurrent protection circuit block (OCP)

The timer-latch overcurrent protection circuit is actuated upon completion of the soft-start period. When an overcurrent flows, the circuit detects the increase in the voltage between the FET’s drain and source using the external FET ON resistor, actuates the timer circuit, and starts charging the capacitor CSCP con-nected to the CSCP terminal (pin 8). If the overcurrent remains flowing beyond the predetermined period of time, latch is set and OUT terminlas (pin 3,22) of each channel are fixed at “H” level. And the circuit sets the latch to turn off the external FET. The detection current value can be set by resistor RLIM1 connected between the FET’s drain and the ILIM1 terminal (pin 5) and resistor RLIM2 connected between the drain and the ILIM2 terminal (pin 20).

Changing connection enables to detect overcurrent at current sense resistor.

To reset the actuated protection circuit, either the power supply turn off and on again or set the CTL terminal (pin 6) to the “L” level to lower the VREF terminal (pin 17) voltage to 2.4 V (Min) or less. (See “1. Setting Timer- Latch Overcurrent Protection Detection Current” in “ ■ABOUT TIMER-LATCH PROTECTION CIRCUIT”.)

(2) Timer-latch short-circuit protection circuit (SCP Logic, SCP Comp.)

The short-circuit detection comparator (SCP Comp.) detects the output voltage level of Error Amp, and if the error amp output voltage of any channel falls below the short-circuit detection voltage (3.1 V Typ), the timer circuits are actuated to start charging the external capacitor CSCP connected to the CSCP terminal (pin 8).

When the capacitor voltage reaches about 0.73 V, the circuit is turned off the output transistor and sets the dead time to 100 %.

To reset the actuated protection circuit, either the power supply turn off and on again or set the CTL terminal (pin 24) to the “L” level to lower the VREF terminal (pin 17) voltage to 2.4 V (Min) or less. (See “2. Setting Time Constant for Timer-Latch Short-Circuit Protection Circuit” in “ ■ABOUT TIMER-LATCH PROTECTION CIR- CUIT”.)

(3) Under voltage lockout protection circuit (UVLO)

The transient state or a momentary decrease in supply voltage, which occurs when the power supply is turned on, may cause the IC to malfunction, resulting in breakdown or degradation of the system. To prevent such malfunctions, under voltage lockout protection circuit detects a decrease in internal reference voltage with respect to the power supply voltage, turns off the output transistor, and sets the dead time to 100% while holding the CSCP terminal (pin 8) at the “L” level.

The circuit restores the output transistor to normal when the supply voltage reaches the threshold voltage of the undervoltage lockout protection circuit.

(4) Protection circuit operating function table

This table refers to output condition when protection circuit is operating.

Operating circuit	CS1	CS2	OUT1	OUT2
Overcurrent protection circuit	L	L	H	H
Short-circuit protection circuit	L	L	H	H
Under-voltage lockout	L	L	H	H

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