MB3785A

21

s METHOD OF SETTING THE DEAD TIME

When the device is set for step-up inverted output based on the flyback method, the output transistor is fixed to

a full-on state (ON-duty = 100 %) at power switch-on. To prevent this problem, you may determine the voltages

dead time (maximum ON-duty) independently for each channel as shown below.

(1) CH1 and CH2 Channels

When the voltage on the DTC terminals (pins 4 and 9) is higher than the triangular-wave output voltage from

the oscillator, the output transistor turns off. The dead time calculation formula assuming that triangular-wave

amplitude := 0.6 V and triangular-wave minimum voltage := 1.3 V is given below.

When you do not use these DTC terminals, connect them to GND.

(2) CH3 and CH4 Channels

When the voltage on the DTC terminals (pins 28 and 33) is lower than the triangular-wave output voltage from

the oscillator, the output transistor turns off. The dead time calculation formula assuming that triangular-wave

amplitude := 0.6 V and triangular-wave maximum voltage := 1.9 V is given below.

Duty (OFF)

0.6

:=

Figure 9. When Using DTC to Set Dead Time

Figure 10. When Not Using DTC

DTC1

(DTC2)

Vdt

19

DTC1

(DTC2)

Duty (OFF)

0.6

:=