HD66724 Datasheet, PDF (71/117 Pages) Hitachi Semiconductor – (Graphics LCD Controller/Driver with Key Scan Function)

HD66724/HD66725
When an Internal Booster and External Bleeder-Resistors are Used
When internal operational amplifiers cannot fully drive the LCD panel used, V1 to V5 voltages can be
supplied through external bleeder-resistors (figure 39). 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, contrast must be
adjusted externally. Connection of external bleeder-resistors can specify a given bias value from 1/2 to 1/6.
Figure 39 shows connection for 1/6-bias drive voltage generation. Double- and triple-boosters can be used
as they are.
OPOFF = Vcc
VLCD
HD66724/5
GND
Vci
VR
V1OUT
R _V2OUT
R _V3OUT
2R
V4OUT
R _V5OUT
R
GND
Vci
C1+
0.47 µF ⁺
to 1 µF
C1-
C2+
0.47 µF ⁺
to 1 µF
C2-
+
-
V1
+
-
V2
+
-
V3
LCD
driver
+
-
V4
+
-
V5
GND
Booster
SEG1 to SEG72 (96)
COM1 to COM24
COMS1 to COMS2
VLOUT
+ _{0.47 µF}
to 1 µF
GND
Notes:
1. Resistance of each external bleeder resistor should be 4.7 kΩ to 25 kΩ.
2. The bias current value for driving LCDs can be varied by adjusting the resistance (2R)
between the V3OUT and V4OUT pins.
3. The internal contrast adjuster is disabled; contrast must be adjusted either by controlling the
external variable resistor between VLCD and V1 for the booster.
4. Vci is both a reference voltage and power supply for the booster; connect it to Vcc directly or
combine it with a transistor so that sufficient current can be obtained.
5. Vci must be smaller than Vcc.
Figure 39 Circuit Using External Bleeder-Resistors
71