BD9E303EFJ-LB Datasheet, PDF (18/31 Pages) Rohm – Over-Current Protection

BD9E303EFJ-LB
Datasheet
Selection of Components Externally Connected
Parameters required to design a power supply are as follows.
Parameter
Input Voltage
Output Voltage
Switching Frequency
Inductor ripple current
ESR of the output capacitor
Output capacitor
Soft-start time
Max output current
Unit
V_IN
V_OUT
FOSC
∆IL
RESR
COUT
TSS
IOMAX
Value Example
24 V
5V
300kHz(Typ)
1.3A
10mΩ
44μF
2.5ms(Typ)
3A
1. Switching Frequency
Switching frequency is fixed to FOSC = 300kHz (Typ).
2. Output Voltage Set Point
The output voltage value can be set by the feedback resistance ratio.
V_OUT
R₁ R₂
R₂
1.0 [V]
※ Minimum pulse range that can be produced at the output
stably through all the load area is 200nsec for
BD9E303EFJ-LB.
Use input/output condition which satisfies the following
method.
Figure 41. Feedback Resistor Circuit
200 nsec
≤_V
V
IN
OUT
F_OSC
3. Input capacitor configuration
For input capacitor, use a ceramic capacitor. For normal setting, 10μF is recommended, but with larger value, input ripple
voltage can be further reduced. Also, for capacitance of input capacitor, take temperature characteristics, DC bias
characteristics, etc. into consideration to set minimum value to no less than 4.7μF.
4. Output LC Filter
The DC/DC converter requires an LC filter for smoothing the output voltage in order to supply a continuous current to the
load. Selecting an inductor with a large inductance causes the ripple current ∆IL that flows into the inductor to be small,
decreasing the ripple voltage generated in the output voltage, but it is not advantageous in terms of the load transient
response characteristic. Selecting an inductor with a small inductance improves the transient response characteristic but
causes the inductor ripple current to be large, which increases the ripple voltage in the output voltage, showing a trade-off
relationship. Here, select an inductance so that the size of the ripple current component of the inductor will be 20% to 50%
of the Max output current (3A).
VIN
I_L
Inductor saturation current > I_OUTMAX +∆I_L /2
IOUTMAX
∆I_L
Average inductor current
t
Driver
L
VOUT
C_OUT
Figure 42. Waveform of current through inductor
Figure 43. Output LC filter circuit
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18/28
TSZ02201-0J3J0AJ00650-1-2
13.Feb.2015 Rev.002