BD9E300EFJ-LB Datasheet, PDF (21/33 Pages) Rohm – 7.0V to 36V Input, 2.5A Integrated MOSFET Single Synchronous Buck DC/DC Converter

BD9E300EFJ-LB
ΔV _RPL
=
0.84
×
(10m
+
8
×
1
44μ
×
1M
)
=
11
[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 3.8 [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 [mV]
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
[A]
where :
C _OUT is the output capacitance
C _LOAD is the output load capacitance
T_SS is the soft start time
From the above equation, VIN = 24V, VOUT = 5V, L = 4.7μH, IOMAX = 2.5A (max), switching frequency FOSC = 850kHz (min),
the output capacitor COUT = 44μF, TSS = 1.5ms 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) <
(3.8
- I _OMAX - ΔI _L /2) × T_SS
V_OUT
- C _OUT
=
197
[ μF]
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21/30
TSZ02201-0J3J0AJ00220-1-2
21.Feb.2014 Rev.002