pcf8812 NXP Semiconductors, pcf8812 Datasheet - Page 17

• Manufacturer Part Number: pcf8812
• Description: 65 X 102 Pixels Matrix Lcd Driver
• Manufacturer: NXP Semiconductors

Philips Semiconductors
10.9
Due to the temperature dependency of the liquid crystals
viscosity the LCD controlling voltage V
increased with lower temperature to maintain optimum
contrast. There are 4 different temperature coefficients
available in the PCF8812 (see Fig.13). The coefficients
are selected by bits TC1 to TC0. Table 6 shows the typical
values of the different temperature coefficients. The
coefficients are proportional to the programmed V
10.10 Set V
The operating voltage V
generated voltage is dependent on temperature,
programmed Temperature Coefficient (TC) and the
programmed voltage at reference temperature (T
The voltage at reference temperature V
be calculated as follows:
2004 Feb 23
handbook, halfpage
65
V
V LCD
LCD T
Temperature control
102 pixels matrix LCD driver
V
Fig.13 Temperature coefficients.
OP
LCD
=
value
a
T
+
=
V
T
OP
cut
LCD
b
=
can be set by software. The
T cut
1
a
+
+
T T
V
OP
–
LCD
LCD
cut
b
must be
(T = T
MGS402
TC
T
cut
cut
LCD
).
) can
.
(1)
(2)
17
The parameters are explained in Table 6. The maximum
voltage that can be generated is dependent on the V
voltage and the display load current. Two overlapping
V
control’. For the LOW (PRS = 0) range a = a
HIGH (PRS = 1) range a = a
ranges. It should be noted that the charge pump is turned
off if V
(see Fig.14).
For MUX 1 to 65 the optimum operating voltage of the
liquid can be calculated as follows;
where V
material used.
Table 6 Typical values for parameters for the
As the programming range for the internally generated
V
(9 V) the user has to ensure, while setting the V
and selecting the Temperature Compensation (TC), that
under all conditions and including all tolerances that V
remains below 9 V.
a1
a2
b
T
LCD
LCD
cut
SYMBOL
ranges are selectable via the command ‘HV-gen
allows values above the maximum allowed V
V
OP
LCD
th
6 to 0 and the bit PRS are all set to zero
HV-generator programming
is the threshold voltage of the liquid crystal
=
-------------------------------------- -
2
2.94 (bit PRS = 0)
6.75 (bit PRS = 1)
0.03
27
1
+
1
–
65
VALUE
----------
1
65
2
with steps equal to ‘b’ in both
V
th
=
Product specification
6.85 V
V
V
V
C
PCF8812
1
UNIT
and for the
OP
th
register
LCD
DD2
LCD
(3)