BD9E303EFJ-LB Datasheet, PDF (19/31 Pages) Rohm – Over-Current Protection

BD9E303EFJ-LB
Datasheet
Now calculating with VIN = 24V, VOUT = 5V, switching frequency FOSC = 300kHz, ∆IL is1.3A, inductance value
That can be used is calculated as follows:
L V_OUT
V _IN ‐V_OUT
V _IN
1
F_OSC
ΔI _L
10.15 ≒10 μH
* If the output voltage setting is larger than half of VIN please calculated as follows:
L
4
V _IN
F_OSC ΔI _L
Also for saturation current of inductor, select the one with larger current than maximum output current added by 1/2 of
inductor ripple current ∆IL.
Output capacitor COUT affects output ripple voltage characteristics. Select output capacitor COUT so that necessary ripple
voltage characteristics are satisfied.
Output ripple voltage can be expressed in the following method.
ΔV _RPL ΔI _L
R _ESR
1
8 C _OUT F_OSC
With COUT = 44µF, RESR = 10mΩ the output ripple voltage is calculated as
ΔV_RPL 1.3
10m
8
1
44μ 300k
25.31 [mV]
* When selecting the value of the output capacitor COUT, please note that the value of capacitor CLOAD will add up to
the value of COUT to be connected to VOUT_.
Charging current to flow through the CLOAD, COUT and the IC startup, must be completed within the soft-start time this
charge. Over-current protection circuit operates when charging is continued beyond the soft-start time, the IC may not
start. Please consider in the calculation the condition that the lower maximum value capacitor CLOAD that can be
connected to VOUT (max) is other than COUT.
Inductor ripple current maximum value of start-up (ILSTART) < Over Current Protection Threshold 4.25 [A](min)
Inductor ripple current maximum value of start-up (ILSTART) can be expressed in the following method.
ILSTART = Output maximum load current(IOMAX) + Charging current to the output capacitor (ICAP) +
∆IL
2
Charging current to the output capacitor (ICAP) can be expressed in the following method.
I _CAP
C _OUT
C _LOAD
T_SS
V_OUT
From the above equation, VIN = 24V, VOUT = 5V, L = 10μH, IOMAX = 3.0A (max), switching frequency FOSC = 255kHz (min),
the output capacitor COUT = 44μF, TSS = 1.25ms soft-start time (min), it becomes the following equation when calculating
the maximum output load capacitance CLOAD (max) that can be connected to VOUT.
C _LOAD max
4.25 ‐ I _OMAX ‐ ΔI _L /2
V _OUT
T_{SS ‐ C OUT}
74.5 [ μF]
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TSZ22111•15•001
19/28
TSZ02201-0J3J0AJ00650-1-2
13.Feb.2015 Rev.002