BD9D321EFJ Datasheet, PDF (16/28 Pages) Rohm – 4.5V to 18V Input, 3.0A Integrated MOSFET 1ch Synchronous Buck DC/DC Converter

BD9D321EFJ
Datasheet
IL
Inductor saturation current > I_OUTMAX +⊿I_L /2
⊿I_L
Average inductor current
(Output Current：IOUT)
t
Figure 29. Waveform of current through inductor
Figure 30. Output LC filter circuit
The inductor peak to peak ripple current ⊿IL is calculated using the following equation.
ΔI_L
= V_OUT
× (V_IN－V_OUT ) × _VIN
1
× F_OSC
×L
[A]
For example, with VIN = 12 V, VOUT = 1.8 V, L = 2.2µH and the switching frequency F_OSC = 700 kHz, the calculated peak
current ⊿IL is 1.0A.
Then, the inductor saturation current must be larger than the sum of the maximum output current (IOUTMAX) and 1/2 of the
inductor ripple current (∆IL / 2).
The output capacitor C_OUT affects the output ripple voltage characteristics. The output capacitor C_OUT must satisfy the
required ripple voltage characteristics.
The output ripple voltage can be represented by the following equation.
ΔV_RPL
=
ΔI _L
× (R_ESR
+
1
8 × C_OUT
× F_OSC
)
[V]
R_ESR is the Equivalent Series Resistance (ESR) of the output capacitor.
※The capacitor rating must allow a sufficient margin with respect to the output voltage.
The output ripple voltage can be decreased with a smaller ESR.
A ceramic capacitor of about 22 µF to 100 µF is recommended.
※Pay attention to total capacitance value, when additional capacitor CLOAD is connected in addition to output capacitor
COUT. Then, please determine CLOAD and soft start time Tss (Refer to (3) Soft Start Setting) as satisfying the following
equation.
C_OUT
+ C_LOAD
≤
(I_OCP－I_OUT ) ×T_SS
V_OUT
IOCP is Over Current Protection Current limit value.
[μF]
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TSZ22111•15•001
16/25
TSZ02201-0J3J0AC00490-1-2
07.Aug.2013 Rev.001