MB39A214APFT-G-JNERE1 Datasheet, PDF (27/56 Pages) Fujitsu Component Limited. – 2ch DC/DC converter IC with PFM/ PWM synchronous rectification

MB39A214A
Minimum power supply voltage
The maximum on duty is limited by "the minimum off time (t_OFFMIN) that an IC holds without fail as a fixed
value" and "the on time (t_ON) determined by the power voltage value and the output voltage setting value".
The ratio between the output voltage and the power voltage must be less than the maximum on duty.
The minimum power supply voltage that is required to sustain the output voltage can be calculated by the
following formula.
V_{IN_MIN} =
(V_OUT + I_{OUT_MAX} ¯ (RDC + R_{ON_Main})) ¯ V_OUT
V_OUT − (V_OUT + I_{OUT_MAX} ¯ (RDC + R_{ON_Sync})) ¯ t_{OFF_MIN} ¯ f_OSC ¯1.2
V_{IN_MIN}
V_OUT
I_{OUT_MAX}
R_{ON_Main}
R_{ON_Sync}
RDC
: Power supply voltage [V]
: Output setting voltage [V]
: Maximum load current value [A]
: ON resistance of high-side FET [Ω]
: ON resistance of low-side FET [Ω]
: Series resistance of inductor [Ω]
f_OSC
t_{OFF_MIN}
: Switching frequency setting value [Hz]
: Minimum off time (Maximum value) [s]
(For the minimum off time, see “ON/OFF Time [Minimum OFF time ] ” in
“„ELECTRICAL CHARACTERISTICS”.)
Use the smaller switching frequency setting in order to make the voltage output possible with the lower
power voltage.
Slope voltages
It is necessary to sustain the Slope voltage 15 mV or higher in order to obtain the stable switching cycle.
The Slope voltage can be calculated by the following formula.
V_Slope =
(V_IN − V_OUT) ¯ V_OUT ¯ R_{ON_Sync}
L ¯ V_IN ¯ f_OSC
V_Slope
V_IN
V_OUT
f_OSC
R_{ON_Sync}
L
: Slope voltage [V]
: Power supply voltage [V]
: Output setting voltage [V]
: Switching frequency [Hz]
: ON resistance of low-side FET [Ω]
: Inductor value [H]
DS405-00007-1v0-E
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