MB39A214APFT-G-JNERE1 Datasheet, PDF (36/56 Pages) Fujitsu Component Limited. – 2ch DC/DC converter IC with PFM/ PWM synchronous rectification

MB39A214A
Selection of fly-back diode
This device is improved by adding the fly-back diode when the conversion efficiency improvement or the
suppression of the low-side FET fever is desired, although those are unnecessary to execute normally. The
effect is achieved in the condition where the switching frequency is high or output voltage is lower. Select
schottky barrier diode (SBD) that the forward current is as small as possible. In this DC/DC control IC, the
period for the electric current flow into fly-back diode is limited to dead time period because the
synchronous rectification system is adopted. (as for the dead time, see “Output Block” in “ELECTRICAL
CHARACTERISTICS”). Each rating for the fly-back diode can be calculated by the following formula.
I_D ≥ I_{OUT_MAX} ¯f_OSC ¯ (t_D1 + t_D2)
I_D
: Forward current rating of SBD [A]
I_{OUT_MAX} : Maximum load current [A]
f_OSC : Switching frequency [Hz]
t_D1, t_D2 : Dead time [s]
I_FSM ≥ I_{OUT_MAX} + ^ΔIL
2
I_FSM : Peak forward surge current ratings of SBD [A]
I_{OUT_MAX} : Maximum load current [A]
ΔI_L : Ripple current peak-to-peak value of inductor [A]
V_{R_Fly} > V_IN
V_{R_Fly} : Reverse voltage of fly-back diode direct current [V]
V_IN
: Power supply voltage [V]
36
DS405-00007-1v0-E