µ PC1935
3.5.3 Channel 3 (for inverted output)
The ON/OFF signal control method of the output oscillation of channel 3 is to input the ON/OFF signal from ON3 as
shown in Figure 3-5. The PWM converter can be turned ON/OFF by controlling the level of the DTC3 pin. However, it is
necessary to keep the level of the FB3 output high so that the timer latch does not start when the PWM converter is OFF.
In this circuit example, the FB3 output level is controlled by controlling the level of the II3 pin.
Because channel 3 supports an inverted converter, its PWM comparator logic is different from that of channels 1 and 2.
Figure 3-5 ON/OFF Control (channel 3: for inverted output)
ON3
Q33
Q31
VREF
R31
R32
–VO3
(Converter
output voltage)
FB3
II3
–
SCP comparator
(common to each channel) DLY
+
+ Error
Q1
0.3 V amplifier
–
0.63 V
Q32
VREF
R33
C31
To output stage
–
–
+
PWM comparator
DTC3
R34
Oscillation section
(common to each channel)
CDLY
(1) When ON3 is high: OFF status
Q31: ON → Q32: ON → DTC3 pin: High level → Output duty of PWM comparator: 0 %
Q33: ON → II3 pin: Low level → FB3 output: High level → SCP comparator output: High level → Q1 is ON.
→ Timer latch stops.
(2) When ON3 is low: ON status
Q31: OFF → Q32 is OFF. → C31 is charged in the sequence of [VREF → C31 → R34] → DTC3 pin voltage drops.
→ Soft start
Q33: OFF → II3 pin: High level → FB3 output: Low level → SCP comparator output: Low level → Q1: OFF
→ Charging CDLY starts (timer latch start).
Caution Keep the high-level voltage of the DTC3 pin at 1.6 V or higher and the low-level voltage of the II3 pin
within 0.3 V. The maximum voltage that is applied to the II3 pin must be equal to or lower than VREF.
Data Sheet G13418EJ3V0DS00
19