BD9E302EFJ Datasheet, PDF (32/44 Pages) Rohm – Integrated MOSFET Single Synchronous Buck DC/DC Converter

BD9E302EFJ
Datasheet
* When selecting the value of the output capacitor COUT, please use ceramic capacitor and please note that the value
of capacitor CLOAD connected to VOUT will be added up to the value of COUT. Charging current to flow through the
CLOAD, COUT when the IC startup, must be completed this charge within the soft-start time. Over-current protection
circuit operates when charging is continued beyond the soft-start time, the IC may not start. The maximum CLOAD that
can be connected to VOUT is calculated by the equation below.
Inductor ripple current maximum value of start-up (ILSTART) < Over Current Protection Threshold 4.16 [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 = 12V, VOUT = 5V, L = 4.7μH, IOMAX = 3.0A (Max), switching frequency FOSC = 484kHz (Min),
∆IL=1.282A (Max), the output capacitor COUT = 44μF, TSS = 1.2ms 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
4.16 ‐ I_OMAX ‐ ΔI _L /2
V_OUT
T_{SS ‐ C OUT}
80.56 [ μF]
5. Input voltage start-up
Figure 77. Input Voltage Start-up Time
Soft-start function is designed for the IC so that the output voltage will start according to the time that was decided
internally. After UVLO release, the output voltage range will be less than 70% of the input voltage at soft-start operation.
Please be sure that the input voltage of the soft-start after startup is as follows.
V _IN
≥^VOUT
0.85
0.7
[V]
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27.Apr.2016 Rev.002