PCF8820U Philips Semiconductors, PCF8820U Datasheet - Page 8

• Manufacturer Part Number: PCF8820U
• Description: 67 x 101 Grey-scale/ECB colour dot matrix LCD driver
• Manufacturer: Philips Semiconductors

Philips Semiconductors
7.11
The bias voltage generator generates 4 buffered
intermediate LCD bias voltages. It contains 4 operational
amplifiers and an input reference voltage generator. It can
operate in two voltage ranges:
7.12
The high voltage generator contains a voltage multiplier
which uses a charge pump circuit supplied by V
V
The multiplier is software programmable with a factor from
2 to 8. In the direct drive mode the output voltage
V
7.13
The viscosity of the liquid crystal depends on the
temperature; so to maintain optimum contrast at lower
temperatures V
shows V
high multiplex rate liquid crystal.
Linear temperature compensation is supported in the
PCF8820. The temperature coefficient for V
set to one of 8 values by setting bits TC
2000 Dec 07
handbook, halfpage
DD3
LCDOUT
Normal mode (from 7.0 to 14.5 V)
Partial screen mode (from 4.5 to 14.5 V).
67 101 Grey-scale/ECB colour dot matrix
LCD driver
(1) LCD characteristic.
(2) Linear temperature compensation.
Fig.2
.
V LCD
(V)
Bias voltage generator
High voltage generator
Temperature compensation
LCD
= V
LCD supply voltage as a function of the
temperature.
DD2
as a function of the temperature for a typical
LCD
.
needs usually to be increased. Fig.2
0
2
to TC
LCDOUT
T amb ( C)
MGT123
0
DD2
.
(1)
(2)
can be
and
8
7.14
The PCF8820 has a built-in temperature sensor. The
sensor monitors the temperature and writes an 8-bit
number into the status register. The temperature sensor
and status register can both be accessed via the I
interface controller.
The temperature sensor allows any temperature
compensation to be implemented; any programmable
parameter can be optimized as a function of the sensor
read-out temperature.
7.15
The LCD waveforms are shown in Figs 3, 4 and 5.
At frame inversion, the PCF8820 generates a dummy row
cycle, where no row is selected. This ensures equal
conditions for the first row after frame inversion as for the
other rows. Therefore the effective multiplex rate in all
modes is 1 : (multiplex rate + 1).
7.16
DDRAM to display mapping is shown in Fig.6.
Temperature sensor
LCD driver waveforms
DDRAM to display mapping
Product specification
PCF8820
2
C-bus