MB3827 Datasheet, PDF (32/41 Pages) Fujitsu Component Limited. – 6-ch DC/DC Converter IC With Synchronous Rectification for voltage step-up and step-down

MB3827
s METHOD OF SETTING THE DEAD TIME
When setting step-up/step-down switching, Zeta type, or fly-back type step-up or inverter output, the output
transistor at start-up is in full-on (ON duty cycle = 100%) state. To prevent this, the DTC voltage from the DTC1-
1 terminal (pin 43) to the DTC6 terminal (pin 15) voltage is determined from the VREF voltage, as shown in
following figure , so that the output transistor dead time (the maximum value of the ON interval) can be set easily.
When the voltage on the DTC5 and DTC6 terminals 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 am-
plitude =: 0.7 V and triangular-wave maximum voltage =: 1.8 V is given below.
DUTY(ON)max =:
Vdt − 1.1
0.7
×
100[%],
Vdt
=
Rb
Ra + Rb
× VREF
When you do not use these DTC5 and DTC6 terminals, connect then to VREF terminal (pin 24) as shown
following figure (Not setting the channel 5,6 dead time).
Setting the channel 5, 6 dead time (same as for other channels)
VREF ²⁴
DTC5 ¹⁶
Ra
Rb
Vdt
VREF ²⁴
DTC6 ¹⁵
Ra
Rb
Vdt
Not setting the channel 5,6 dead time (same as for other channels)
VREF ²⁴
DTC5 ¹⁶
VREF ²⁴
DTC6 ¹⁵
32