HD66717 Datasheet, PDF (53/90 Pages) Hitachi Semiconductor – (Low-Power Dot-Matrix Liquid Crystal Display Controller/Driver)

HD66717
When an Internal Booster and Internal Operational Amplifiers are Used
To supply LCD drive voltage using the internal booster, circuits should be connected as shown in Figure
31. Here, contrast can be adjusted through the CT bits of the contrast-control instruction. Temperature
can be compensated either through the CT bits or by controlling the reference voltage for the booster (Vci
pin) using a thermistor.
Note that Vci is both a reference voltage and power supply for the booster; the reference voltage must
therefore be adjusted using an emitter-follower or a similar element so that sufficient current can be
supplied. In this case, Vci must be equal to or smaller than the V_CC level.
The HD66717 incorporates a voltage-follower operational amplifier for each of V1 to V5 to reduce
current flowing through the internal bleeder-resistors, which generate different levels of liquid-crystal
drive voltages. Thus, potential differences between V_CC and V1 and between V_EE and V5 must be 0.4V or
greater. Note that the OPOFF pin must be grounded when using the operational amplifiers.
a) Double boosting
OPOFF = GND
V_CC
Short-circuited
for 1-or 2-line
display
V_CC ^HD66717
R
V2 ^R
R
+– ^V1
+– V2
V3 ^R
R
R
VR
V_EE
+– ^V3
+– ^V4
+– ^V5
Vci
C1
0.47 µF
to 1 µF + ^C2
0.47 µF
to 1 µF ₊
V5OUT2
V5OUT3
GND
Booster
b) Triple boosting
OPOF = GND
V_CC
Short-circuited
for 1-or 2-line
display
V_CC ^HD66717
R
V2 ^R
R
+– ^V1
+– V2
V3 ^R
R
R
VR
V_EE
+– ^V3
+– ^V4
+– ^V5
Vci
C1
0.47 µF
to 1 µF ⁺
C2
V5OUT2
+
0.47 µF
to 1 µF
GND
V5OUT3
Booster
+
GND
Note: 1. The reference voltage input (Vci) must be adjusted so that the output voltage after boosting will not exceed
the absolute maximum rating of the liquid-crystal power supply voltage (15V). Particularly, Vci must be
5 V or less for triple boosting.
2. 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.
3. Vci must be smaller than V_CC.
4. To operate the voltage-follower correctly, potential differences between V_CC and V1 and between V5 and
V_EE must be 0.4V or greater, particularly for low-duty drive such as 1-line display.
5. Polarized capacitors must be connected correclty.
6. Circuits for temperature compensation should be designed based on the sample circuit shown in Figure 32.
Figure 31 Internal Power Supply Circuit Example for LCD Drive Voltage Generation
505