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参数资料
| 型号： | BD8151EFV-E2 |
| 厂商： | Rohm Semiconductor |
| 文件页数： | 10/20页 |
| 文件大小： | 0K |
| 描述： | IC PWR SUPPLY 1CH 20HTSSOP |
| 标准包装： | 2,500 |
| 应用： | LCD 监视器，笔记本电脑显示器 |
| 电流 - 电源： | 1.2mA |
| 电源电压： | 2.5 V ~ 5.5 V |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 20-TSSOP（0.173"，4.40mm 宽） |
| 供应商设备封装： | 20-HTSSOP-B |
| 包装： | 带卷 (TR) |
BD8151EFV, BD8157EFV
Technical Note
(4) Selecting the output rectification diode
Schottky barrier diode is recommended as the rectification diode to use at the DC/DC converter output stage. Select the
diode paying attention to the max. inductor current and max. output voltage.
Max. Inductor current I INMAX + ? I L < Rating current of diode
Max. output voltage V OMAX
< Rating voltage of diode
Since each parameter has 30% to 40% of dispersion, be sure to design providing sufficient margins.
(5) Design of the feedback resistor constant
Refer to the following equation to set the feedback resistor. As the setting range, 10 k ? to 330 k ? is recommended. If the
resistor is set to a 10 k ? or lower, it causes the reduction of power efficiency. If it is set to 330 k ? or larger, the offset
voltage becomes larger by the input bias current 0.4 μA (Typ.) in the internal error amplifier.
Step-up
Vo =
R8 + R9
R9
? 1.245
[V]
Vo
R8
2
Reference voltage 1.245 V
＋
ERR
－
R9
FB
Fig. 31Feedback Resistance Setting
(6) Setting the soft start time
Soft start is required to prevent the coil current at the time of startup from increasing
and the overshoot of the output voltage at the starting time. Fig. 32 shows the
relation between the capacitance and soft start time. Please refer to it to set the
capacitance.
As the capacitance, 0.001 μF to 0.1μF is recommended. If the capacitance is set to
0.001 μF, the overshooting may occur on the output voltage. If the capacitance is
set to 0.1 μF or larger, the excessive back current flow may occur in the internal
10
1
0.1
parasitic elements when the power is turned OFF and it may damage IC. When the
capacitor of 0.1 μF or larger is used, be sure to insert a diode to Vcc in series, or a
bypass diode between the SS pin and VCC.
0.01
0.001
0.01
SS CAPACITANCE[uF]
0.1
Bypass diode
Back current prevention diode
Fig.32 SS Pin Capacitance vs
Delay Time
VCC
Output pin
Fig. 33 Bypass Diode Example
When there is the startup relation (sequences) with other power supplies, be sure to use the high accuracy product (such as X5R).
Soft start time may vary according to the input voltage, output voltage loads, coils and output capacity. Be sure to verify the
operation using the actual product.
(7) Setting the ENB pin
When the ENB pin is set to Hi, the internal circuit becomes active and the DC/DC converter starts operating. When it is set
to Low, the shut down is activated and all circuits will be turned OFF.
(8) Setting the frequency by FCLK
It is possible to change the switching frequency by setting the FCLK pin to Hi or Low. When it is set to Low, the product
operates at 600 kHz (Typ.). When it is set to Hi, the product operates at 1,200 kHz (Typ.).
www.rohm.com
? 2009 ROHM Co., Ltd. All rights reserved.
10/17
2009.07 - Rev.B
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