MB3827 Datasheet, PDF (21/41 Pages) Fujitsu Component Limited. – 6-ch DC/DC Converter IC With Synchronous Rectification for voltage step-up and step-down

MB3827
2. Channel Control Function
Channel on and off levels are dependent on the voltage levels of the CTL1-4,7 terminal (pin 27), XENB1-6
terminal (pin 4), CTL5 terminal (pin 28), and CTL6 terminal (pin 29).
CTL1-4,7
L
H
Each Channel On/Off Setting Conditions.
Voltage level of CTL pin
Channel on/off setting conditions
XENB1-6
CTL5
CTL6 Power CH7 CH1 to 4
CH5
CH6
X
X
X
OFF (standby state)
H
X
X
OFF
OFF
L
ON
L
H
ON
ON
L
ON
L
OFF
H
OFF
H
ON
Note: When the RB1 pin is connected to the VREF pin, the OUT1-3 and OUT1-4 pins are held at “L” level.
X : Don’t care.
3. Protective Functions
(1) Timer-latch short 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 −IN(C)8 terminal (pin 23) voltage falls below the reference
voltage, the timer circuit starts operating and the capacitor CSCP connected to the CSCP terminal (pin 31) starts
charging.
When the capacitor voltage reaches approximately 0.68 V, the output transistor is turned off and the dead time
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. Malfunction like the above-mentioned will be
prevented, 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 31) 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.
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