Technical Note
5/16
BH76906GU, BH76909GU, BH76912GU, BH76916GU, BH76706GU
www.rohm.com
2009.03 - Rev.A
© 2009 ROHM Co., Ltd. All rights reserved.
C1 NVCC
-VCC
(-2.75 V)
Flying capacitor “-“ pin (8pin)
B1
C_MINUS
0V
↑↓
-VCC
(-2.75 V)
Note 1) DC voltages in the figure are those when VCC ＝ 3.0 V. Moreover, these values are reference values which are
not guaranteed.
Note 2) Numeric values in the figure are settings which do not guarantee ratings.
●Description of Operation
1) Principles of output coupling capacitorless video drivers
For an amplifier operated from a single power supply (single-supply), since the operating point has a potential of
approximately 1/2 Vcc, a coupling capacitor is required for preventing direct current in the output. Moreover, since the
load resistance is 150 (75 + 75 ) for the video driver, the capacity of the coupling capacitor must be on the order of
1000 F if you take into account the low band passband. (Fig.3)
For an amplifier operated from dual power supplies (+ supply), since the operating point can be at GND level, a coupling
capacitor for preventing output of direct current is not needed.
Moreover, since a coupling capacitor is not needed, in principle, there is no lowering of the low band characteristic at the
output stage. (Fig.4)
2) Occurrence of negative voltage due to charge pump circuit
A charge pump, as shown in Fig. 5, consists of a pair of switches (SW1, SW2) and a pair of capacitors (flying capacitor,
anchor capacitor). Switching the pair of switches as shown in Fig. 5 causes a negative voltage to occur by shifting the
charge in the flying capacitor to the anchor capacitor as in a bucket relay.
In this IC, by applying a voltage of +3 V, a negative voltage of approximately -2.8 V is obtained.
0V
NVC
C1
C2
VCC
C2
NVCC
GND
VCC
GND
VCC
VCC
NVC
Negative voltage pin (7pin)
Dual-supply amplifier
VCC
-VCC
75Ω
75Ω
Single-supply amplifier
VCC
75Ω
75Ω
1/2 VCC bias
1000μF
Fig.3 Fig.4
Output capacitor required since DC
voltage is occurring at output pin
Output capacitor not required since
DC voltage does not occur at output
pin
C_MINUS
