BD9B301MUV-LB Datasheet, PDF (22/33 Pages) Rohm – Over Current Protection

BD9B301MUV-LB
Datasheet
Charge current to output capacitor I_CAP can be expressed using the following equation.
I _CAP
C _OUT
C _LOAD
T_SS
V_{OUT [A]}
For example, given VIN= 5V, VOUT= 3.3V, L= 1.5µH, switching frequency F_OSC= 800kHz(Min), Output capacitor COUT=
44µF, Soft Start time TSS= 0.5ms(Min), and load current during soft start IOSS= 3A, maximum C_LOAD can be computed
using the following equation.
C _LOAD max
3.8 ‐ I_OSS ‐ ΔIL /2
V_OUT
T_{SS ‐ C OUT  6.38 μF}
If the value of CLOAD is large, and cannot meet the above equation, adjust the value of the capacitor CSS to meet the
condition below.
C _LOAD max
3.8 ‐ I_OSS ‐ ΔI _L /2
V_OUT I _SS
V _FB
C _SS ‐ C _OUT
(Refer to the following items (3) Soft Start Setting equation of time TSS and soft-start value of the capacitor to be
connected to the CSS.)
For example, given VIN = 5V, VOUT = 3.3V, L = 1.5µH, load current during soft start IOSS = 3A, switching frequency FOSC=
800kHz (Min), Output capacitor COUT = 44µF, VFB = 0.792V(Max), ISS = 2.0µA(Max), with CLOAD = 220uF, capacitor CSS
is computed as follows.
C _SS
V_OUT I _SS
3.8 ‐ I_OSS ‐ ΔI _L /2 V_FB
C _LOAD C _OUT
6617 pF
2. Output Voltage Setting
The output voltage value can be set by the feedback resistance ratio.
For stable operation, it is recommended to use feedback resistance R1 of more than 20kΩ.
V_OUT
R1
Error Amplifier
VOUT
R1 R2
R2
0.8 V
FB
R2
0.8V
R2
0.8
VOUT ‐ 0.8
R1 Ω
Figure 51. Feedback Resistor Circuit
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TSZ02201-0J3J0AJ00830-1-2
2015.04.02 Rev.001