BD9B301MUV-LB Datasheet, PDF (21/33 Pages) Rohm – Over Current Protection

BD9B301MUV-LB
Datasheet
Selection of Components Externally Connected
1. Output LC Filter Constant
In order to supply a continuous current to the load, the DC/DC converter requires an LC filter for smoothing the
output voltage. It is recommended to use inductors of values 0.47µH to 1.0µH when FREQ=L or 1.0µH to 1.5µH at
FREQ=H.
IL
Inductor saturation current > I_OUTMAX +⊿I_L /2
IOUTMAX
⊿I_L
Average inductor current
t
Figure 49. Waveform of current through inductor
Figure 50. Output LC filter circuit
Inductor ripple current ∆IL
ΔI _L V_OUT
V _IN -V_OUT
V _IN
1
F_OSC
L
608 mA
Where:
VIN= 5V
VOUT= 1.2V
L=1.5µH
FOSC=1MHz (switching frequency)
The saturation current of the inductor must be larger than the sum of the maximum output current and 1/2 of the inductor
ripple current ∆IL.
The output capacitor COUT affects the output ripple voltage characteristics. The output capacitor COUT must satisfy the
required ripple voltage characteristics.
The output ripple voltage can be represented by the following equation.
ΔV _RPL
ΔI _L
R _ESR
8
1
C _OUT
F_OSC ^{V}
where RESR 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 47 µF is recommended.
*Be careful of total capacitance value, when additional capacitor C_LOAD is connected in addition to output capacitor C_OUT.
Use maximum additional capacitor C_LOAD (Max) condition which satisfies the following condition.
Maximum starting inductor ripple current IL_START Over Current limit 3.8A min
Maximum starting inductor ripple current ILSTART can be expressed using the following equation.
IL_START Maximum starting output current I_OMAX Charge current to output capacitor I_CAP
ΔI _L
2
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2015.04.02 Rev.001