OM6211 NXP Semiconductors, OM6211 Datasheet - Page 11

• Manufacturer Part Number: OM6211
• Description: 48 X 84 Dot Matrix Lcd Driver
• Manufacturer: NXP Semiconductors

Philips Semiconductors
9.11
Due to the temperature dependency of the liquid crystals viscosity, the LCD controlling voltage (V
at lower temperatures to maintain optimum contrast. Figure 4 shows V
multiplex rate liquid.
In the OM6211 the temperature coefficient of V
see Tables 4 and 8.
9.12
The binary number V
can be set by the serial interface command and can be
adjusted (calibrated) by 5 input pins according to the
following formula:
where:
To avoid numerical overflow the allowed values of V
should be limited to the range 32 to 225 (decimal).
The corresponding voltage at the reference temperature,
T
The generated voltage at V
temperature, programmed Temperature Coefficient (TC)
and the programmed voltage at the reference temperature
(T
2002 Jan 17
V
V
handbook, full pagewidth
nom
OP
LCD(Tnom)
nom
V
interface command
V
5 input pins V
V
generation of the LCD supply voltage V
48
PR
OS
OP
, can be calculated as follows:
).
=
is an 8-bit unsigned number set by the serial
is a 5-bit two’s complement number set by the
is an 8-bit unsigned number used internally for
Temperature compensation
V
V
LCD
PR
84 dot matrix LCD driver
=
generator
+
V
a
OS4
OS
+
V
to V
OP
OP
V LCD
representing the operating voltage
OS0
Fig.4 V
b
LCD
, see Table 9
is dependent on the
LCD
as a function of liquid crystal temperature (typical values).
LCD
.
LCD
can be selected from 4 values by setting bits TC
PR
(1)
(2)
11
T
Table 4. The maximum voltage that can be generated is
dependent on the voltage of V
current.
As the programming range for the internally generated
V
user has to ensure while setting the V
selecting the Temperature Compensation, that under all
conditions and including all tolerances the V
maximum 9 V will never be exceeded.
For a particular liquid crystal, the optimum value of V
can be calculated for a given multiplex rate. For a Mux rate
of 1 : 48, the optimum operating voltage of the liquid
crystal can be calculated as follows;
where V
V
V
nom
LCD
LCD
LCD
, a and b for each temperature coefficient are given in
allows values above the maximum allowed V
=
=
th
LCD
-------------------------------------- -
a
is the threshold voltage of the liquid crystal used.
2
+
as a function of temperature for a typical high
1
V
+
OP
1
–
48
----------
b
1
48
T
MGT848
1
V
+
th
TC
=
DD2
6.06 V
and the display load
LCD
T T
Product specification
–
) must be increased
PR
1
and TC
th
nom
register and
OM6211
LCD
0
limit of
,
LCD
LCD
, the
(3)
(4)