MB3825A Fujitsu Microelectronics, Inc., MB3825A Datasheet - Page 28

• Manufacturer Part Number: MB3825A
• Description: 6-ch DC/DC Converter ic With Synchronous Rectifier
• Manufacturer: Fujitsu Microelectronics, Inc.

28
MB3825A
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
full-on state (ON-duty
the DTC3 terminal (pin 31) from the V
ON-duty) independently for each channel as shown Figure.12.
When the voltage on the DTC3 terminal is lower than the triangular-wave (CT1) output voltage from the oscillator,
the output transistor turns off. The dead time calculation formula assuming that triangular-wave amplitude 0.7
V and triangular-wave maximum voltage 1.35 V is given below.
Duty (ON)
When you do not use this DTC3 terminal, connect then to V
Figure 12. When using DTC to set dead time
Figure 13. When not using DTC to set dead time
MAX
Vdt
0.7
Vdt
100 ) at power switch-on.To prevent this problem, you may determine the voltages on
0.65
100 [ ]
27
31
Ra
Rb
REF
VREF
DTC3
voltage so you can easily set the output transistor’s dead time (maximum
27
31
VREF
DTC3
REF
terminal (pin 27) as shown Figure.13..