HD66740 Datasheet, PDF (48/95 Pages) Hitachi Semiconductor – 112 x 80-dot Graphics LCD Controller/Driver

HD66740
Notes on Using Internal Operational Amplifier
The HD66740 has a low-current-consumption-type operational amplifier. When a low-voltage supply
is used, particularly at low temperatures near –20°C, the current in the operational amplifier is reduced.
Therefore, depending on the specifications or display pattern of the LCD panel used, screen quality may
be poor or the LCD panel may not operate at all.
For the operational specifications of the LCD panel, one must consider the drive condition (setting of the
VTEST pin) or the peripheral circuits of the LCD panel in conjunction with the power-supply voltage.
Pin condition for HD66740 (setting VTEST pin):
1. When the power-supply voltage is Vcc ≥ 2.5 V (i.e., the current in the operational amplifier is
sufficient), leave the VTEST pin open (disconnected).
2. When the power-supply voltage is Vcc < 2.5 V (i.e., the current is reduced in the operational
amplifier at low temperature), 1.2 to 1.3 V should be input to the VTEST pin.
The following table and figure correspond to inputs of 1.2 to 1.3 V to the VTEST pin. When higher
LCD drive current is required due to the characteristics of the LCD panel, check the screen quality and
current consumption, adjust the resistance values (R1 and R2), and increase the VTEST pin voltage.
(This is also valid when Vcc ≥ 2.5 V.)
Table 17-a
Vcc
2.4 V
2.0 V
1.8 V
Vcc
R1
R2
GND
to VTEST pin
Vtest = 1.2 to 1.3V
Figure 24-a Circuit to for Generating VTEST Pin Voltage
Settings to Generate VTEST Pin Voltage
R1
270 kΩ
220 kΩ
180 kΩ
R2
330 kΩ
360 kΩ
390 kΩ
Vtest (VTEST Pin Voltage)
1.23 V
1.22 V
1.22 V
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