HD66727 Datasheet, PDF (65/97 Pages) Hitachi Semiconductor – Low-Power Dot-Matrix Liquid Crystal Display Controller/Driver with Key Scan Function

HD66727
When an Internal Booster and External Bleeder-Resistors are Used
When the internal operational amplifiers cannot fully drive the LCD panel used, V1 to V5 voltages can be
supplied through external bleeder-resistors (Figure 37). Here, the OPOFF pin must be set to the V_CC level to
turn off the internal operational amplifiers. Since the internal contrast adjuster is disabled in this case,
contrast must be adjusted externally. Double- and triple-boosters can be used as they are.
V_CC
V_CC
R _V1OUT
R _V2OUT
2R
R
R
VR
V3OUT
V4OUT
V5OUT
V_EE
Vci
C1
0.47 µF
to 1 µF _{+ C2}
V5OUT2
+
0.47 µF
to 1 µF
GND
V5OUT3
0.47 µF
+ _{to 1 µF}
GND
OPOFF = V_CC
HD66727
V_CC
+
–
V1
+
–
V2
+
–
V3
+
–
V4
+
–
V5
Booster
Notes: 1. Resistance of each external bleeder resistor should be 5 kΩ to 15 kΩ.
2. The bias current value for driving liquid-crystals can be varied by adjusting
the resistance (2R) between the V2OUT and V3OUT pins.
3. The internal contrast-adjuster is disabled; contrast must be adjusted either
by controlling the external variable resistor between V_EE and V5OUT or Vci
for the booster.
4. Vci is both a reference voltage and power supply for the booster; connect it to
V_CC directly or combine it with a transistor so that sufficient current can be
obtained.
5. Vci must be smaller than V_CC.
Figure 37 Power Supply Circuit Example Using External Bleeder-Resistor for LCD Drive Voltage
Generation
65