bd8301muv ROHM Co. Ltd., bd8301muv Datasheet - Page 9

• Manufacturer Part Number: bd8301muv
• Description: High-efficiency Step-up/down Switching Regulators With Built-in Power Mosfet
• Manufacturer: ROHM Co. Ltd.

(4) Output voltage setting
○
BD8301MUV
c
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(2) Output capacitor
(3) Setting of oscillation frequency
2009 ROHM Co., Ltd. All rights reserved.
* Note that the above example of frequency setting is just a design target value, and may differ from the actual equipment.
Fig. 23 Oscillation frequency – RT pin resistance
Vpp=⊿IL×
There must be an adequate margin between the maximum rating and output voltage of the capacitor, taking the DC
bias property into consideration.
Output ripple voltage when ceramic capacitor is used is obtained by the following equation.
See Fig. 24 for the relationship between RT and soft-start time.
The internal reference voltage of the ERROR AMP is 0.8 V. Output voltage should be obtained by referring to
Equation (8) of Fig. 25.
A ceramic capacitor with low ESR is recommended for output in order to reduce output ripple.
Setting must be performed so that output ripple is within the allowable ripple voltage.
Oscillation frequency can be set using a resistance value connected to the RT pin (1 pin).
Oscillation frequency is set at 1 MHz when RT = 47 kΩ, and frequency is inversely proportional to RT value.
See Fig. 23 for the relationship between RT and frequency.
Soft-start time changes along with oscillation frequency.
10000
1000
100
2π×f×Co
1
1
RT PIN RESISTANCE [kΩ]
10
R2
R1
VOUT
+ ⊿IL×R
INV
100
ERROR AMP
VREF
0.8V
ESR
1000
Fig. 25 Setting of feedback resistance
[V] ・・・ (5)
9/13
Vo=
Fig. 24 Soft-start time – RT pin resistance
0.1
10
1
(R1+R2)
1
R2
RT PIN RESISTANCE [kΩ]
10
×0.8 [V] ・・・ (8)
100
1000
Technical Note
2009.05 - Rev.B