pcf8535 NXP Semiconductors, pcf8535 Datasheet - Page 12

• Manufacturer Part Number: pcf8535
• Description: 65 X 133 Pixel Matrix Driver
• Manufacturer: NXP Semiconductors

Philips Semiconductors
For calibrating the temperature read-out a measurement
must be taken at a defined temperature. The offset
between the ideal read-out and the actual result has to be
stored into a non-volatile register (e.g. EEPROM):
where TR
PCF8535.
The calibrated temperature read-out can be calculated for
each measurement as follows:
The accuracy after the calibration is 6.7% (plus 1 lsb) of
the difference between the current temperature and the
calibration temperature. For this reason a calibration at or
near the most sensitive temperature for the display is
recommended. E.g. for a calibration at 25 C with the
current temperature at 20 C, the absolute error may be
calculated as:
Absolute error = 0.067
= 3 C + 1 lsb = 4.17 C.
7.12
7.12.1
Due to the temperature dependency of the liquid crystals
viscosity the LCD controlling voltage, Voltage must be
increased at lower temperatures to maintain optimum
contrast. Fig.4 shows V
a typical high multiplex rate liquid.
In the PCF8535 the temperature coefficient of V
selected from 8 values by setting bits TC[2:0]
(see Table 5).
2001 Nov 07
Offset
TR
handbook, halfpage
65
Fig.4
cal
V LCD
=
Temperature compensation
=
T
TR
TR
meas
133 pixel matrix driver
EMPERATURE COEFFICIENTS
V
temperature (typical values).
LCD
meas
ideal
is the actual temperature read-out of the
as function of liquid crystal
–
+
TR
Offset
meas
LCD
[25
as a function of temperature for
0 C
( 20)]
MGS473
LCD
T
can be
(2)
(3)
12
Table 5 Selectable temperature coefficients
7.13
7.13.1
The voltage at the reference temperature (T
calculated as:
The operating voltage, V
The generated voltage is dependent on the temperature,
programmed Temperature Coefficient (TC) and the
programmed voltage at the reference temperature (T
The values for T
The maximum voltage that can be generated is dependent
on the voltage V
Two overlapping V
command page “HV-gen control” (see Fig.5).
The LOW range offers programming from 4.5 to 10.215 V,
with the HIGH range from 10.215 to 15.93 V at T
must be taken, when using temperature coefficients, that
the programmed voltage does not exceed the maximum
allowed V
For a particular liquid, the optimum V
for a given multiplex rate. For a Mux rate of 1 : 65, the
optimum operating voltage of the liquid can be calculated
as:
where V
material used.
V
V
V
LCD
LCD Tcut
LCD
TC2
0
0
0
0
1
1
1
1
=
=
V
th
OP
-------------------------------------- -
S
LCD
a
is the threshold voltage of the liquid crystal
2
ET
TC1
+
=
1
, see Chapter 10.
0
0
1
1
0
0
1
1
V
b V
+
a
OP
1
+
cut
DD2
–
65
VALUE
b V
, a and b are given in Table 6.
OP
----------
OP
1
65
and the display load current.
TC0
ranges are selectable via the
0
1
0
1
0
1
0
1
OP
OP
1
V
, can be set by software.
+
th
=
T T
6.85 V
TC VALUE
0.44
1.10
1.45
1.91
2.15
2.32
2.74
–
LCD
cut
Product specification
0
can be calculated
10
10
10
10
10
10
10
th
PCF8535
TC
3
3
3
3
3
3
3
cut
) can be
cut
UNIT
1/ C
1/ C
1/ C
1/ C
1/ C
1/ C
1/ C
1/ C
. Care
cut
(4)
(5)
(6)
):