MB3883 Datasheet, PDF (28/39 Pages) Fujitsu Component Limited. – 6-ch DC/DC Converter IC With Synchronous Rectification for voltage step-up and step-down

MB3883
s SETTING THE DEAD TIME
When the device is set for step-up inverted output based on the step-up or step-up/down Zeta method or flyback
method, the FB pin voltage may reach and exceed the rectangular wave voltage due to load fluctuation. If this
is the case, the output transistor is fixed to a full-ON state (ON duty = 100 %). To prevent this, set the maximum
duty of the output transistor. To set it, set the voltage at the DTC1 terminal (pin 36) by applying a resistive voltage
divider to the VREF voltage as shown below.
When the voltage at the DTC1 terminal (pin 36) is higher than the triangular wave voltage (CT1), the output
transistor is turned on. The maximum duty calculation formula assuming that triangular wave amplitude =: 0.7
V and triangular wave minimum voltage =: 1.1 V is given below. (Same to other channels.)
DUTY
(ON)
max=:
Vdt − 1.1
0.7 V
V
× 100 (%) , Vdt =
Rb
Ra + Rb
× VREF
When the DTC1 terminal is not used, connect it directly to the VREF terminal (pin 16) as shown below (when
no dead time is set). (Same to other channels.)
VREF ¹⁶
DTC1 ³⁶
Ra
Rb
Vdt
When using DTC to set dead time (Same to other channels.) ( CH1)
VREF ¹⁶
DTC1 ³⁶
When no dead time is set ( Same to other channels.) ( CH 1)
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