IC-SP-06027 R1
5-4. VB power supply
•
The VB power (VB = typ. 7.5V) to be output to the CB pin is generated at the VCC power. The VB power
is supplied to the IC internal circuits such as the triangular wave oscillation circuit, over current detection
circuit and so on.
•
The VB power circuit constitutes a feedback circuit (see Fig. 5-8). To prevent oscillation, connect a
capacitor C0 to the CB pin.
•
The recommended capacity for the C0 is 0.22μF ± 20%. If any value other than the recommended one is
to be used, refer to the below precautions and determine a suitable capacity.
<Precautions>
•
As shown in Fig. 5-9, the CB pin may be oscillated depending on the C0 capacity and the output current
IB.
•
The larger the C0 capacity is, the more stable the VB power supply is. It is recommended, however not to
set the capacity figure to an excessive level. As a guide, it should be 2μ to 3μF or less in the
non-oscillated region.
CB pin
VCC pin
C0
Internal
circuit
IB
Reference
Voltage
source
External
circuit
(Inside the IC)
Fig. 5-8. Equivalent circuit for the VB power supply
Specification: 25mA maximum
10
1
C0 (
μ
Ｆ
)
0.1
Oscillation
0.01
0
5
10
15
20
25
30
Output current IB for VB power supply (mA)
Fig.5-9. IB and C0 dependence of CB pin oscillation (reference data)
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18
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