MB3817 Datasheet, PDF (20/29 Pages) Fujitsu Component Limited. – Switching Regulator Controller

MB3817
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
on the DTC terminals (pin 6) from the VREF voltage so you can easily set the output transistor’s dead time
(maximum ON-duty) independently for each channel as shown below.
When the voltage on the DTC terminals (pin 6) 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 ≅
0.4 V and triangular-wave minimum voltage ≅ 1.4 V is given below.
Duty (ON)MAX ^{.=. Vdt – 1.0 V} × 100 [%]
0.4
When you do not use these DTC terminals, connect them to VREF terminal.
• When using DTC to set dead time
16 _VREF
Ra
6 _DTC
Vdt
Rb
• When not using DTC to set dead time
16 _VREF
6 _DTC
20