Technical Note
5/16
BH76806FVM, BH76809FVM, BH76812FVM, BH76816FVM
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2009.03 - Rev.A
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●Pin descriptions
7 NVCC
-VCC
(-2.75V)
Flying capacitor “-”pin
(8pin)
8 C2
0V
↑↓
-VCC
(-2.75V)
＊1 The DC voltage in the figure is VCC = 3.0 V. These values are for reference only and are not guaranteed.
＊2 These values are for reference only and are not guaranteed.
Description of operations
1) Principles of video driver with no output coupling capacitor
When the amplifier operates using single voltage power supply, the operating potential point is approximately 1/2 Vcc.
Therefore, a coupling capacitor is required to prevent DC output. For the video driver, the load resistance is 150 (75
+ 75 ). Therefore, the coupling capacitor should be about 1000 µF when a low bandwidth for transmission is considered.
(See Figure 3.)
When the amplifier operates using a dual (±) power supply, the operating point can be set at GND level, and therefore,
there is no need for a coupling capacitor to prevent DC output.
Since a coupling capacitor is not needed, there is no sagging of low-frequency characteristics in output stage. (See Figure
4.)
2) Generation of negative voltage by charge pump circuit
As is shown in Figure 5, the charge pump consists of a pair of switches (SW1 and SW2) and a pair of capacitors (flying
capacitor and load capacitor), generating a negative voltage. When +3 V is applied to this IC, approximately -2.83 V of
negative voltage is obtained.
0V
VCC
NVC
C1
C2
VCC
C2
NVCC
GND
VCC
GND
VCC
VCC
NVC
Load voltage pins (7 pins)
Amp (Dual power supply)
VCC
-VCC
75Ω
75Ω
Amp (Single power supply)
VCC
75Ω
75Ω
1/2VCC Bias
1000μF
Fig.3 Fig.4
Output capacitor is required due to DC
voltage at output pin
Output capacitor is not required since
DC voltage is not applied to output pin
