pcf8813 NXP Semiconductors, pcf8813 Datasheet - Page 36

• Manufacturer Part Number: pcf8813
• Description: 67 + 1 X 102 Pixels Matrix Lcd Driver
• Manufacturer: NXP Semiconductors

Philips Semiconductors
11.11 Set HV generator stages
The PCF8813 incorporates a software-configurable
voltage multiplier. After reset (RES) the voltage multiplier
is set to 2
via the set HVgen stages command bits S[1:0].
11.12 Bias system
The bias voltage levels are set in the ratio of
R - R - nR - R - R giving a 1/(n + 4) bias system. Different
multiplex rates require different n factors. This is
programmed by BS[2:0] (see Table 15).
For multiplex rates of 1 : 68 the optimum bias value n is
given by:
Changing the bias system from the optimum value will
have a consequence for the contrast and viewing angle.
One reason to depart from the optimum would be to
reduce the required operating voltage. A compromise
between contrast and operating voltage must be found for
any particular application.
Table 15 Bias system programming
2004 Mar 05
BS[2] BS[1] BS[0]
(67 + 1)
0
0
0
0
1
1
1
1
n
0
0
1
1
0
0
1
1
V
=
DD2
68 3
. Other voltage multiplier factors are set
102 pixels matrix LCD driver
–
0
1
0
1
0
1
0
1
=
5.246
n
7
6
5
4
3
2
1
0
=
1 : 100
1 : 80
1 : 65 or 1 : 67
1 : 48
1 : 34 or 1 : 40
1 : 24
1 : 18 or 1 : 16
1 : 10, 1 : 9 or 1 : 8
MULTIPLEX RATES
5
RECOMMENDED
resulting in
1
/
9
bias.
36
Table 16 LCD bias voltage
Notes
1. Operation of bias level V4 is given for
2.
The operating voltage can be set by software through the
interface. The binary number V
operating voltage can be set according to the following
formula:
Where:
The corresponding voltage at the reference temperature,
T
V
V
V1
V2
V3
V4
V5
V6
CUT
SYMBOL
OP
LCD Tcut
V
generation of the LCD supply voltage V
V
module maker; see Table 17
V
V
(1)
(2)
OP
CAL
PR
PR*
V4 > V
to be selected accordingly.
operation of the bias level V5 is limited to voltages
V5 < V
accordingly.
For multiplex rates equal to or lower than 1 : 24 (n = 2)
, can be calculated as:
=
is an 8-bit unsigned number composed of PRS and
is an 8-bit unsigned number used internally for
set by an interface command.
is a 5-bit twos complement number set by the
V
CAL
SS
DD2,3
=
+ 0.9 V. For higher multiplex rates, V
4:0
a
+
BIAS VOLTAGES
1.1 V. V
V
+
OP
V
PR
-----------------
-----------------
-----------------
-----------------
n
n
n
n
n
n
V
V
b
LCD
+
+
+
+
2
+
1
+
SS
LCD
3
4
2
4
4
4
has to be selected
OP
representing the
Product specification
V
8
7
2
1
V
PCF8813
/
/
/
/
FOR
LCD
9
9
9
9
SS
LCD
VOLTAGES
V
V
V
V
BIAS
LCD
LCD
LCD
LCD
1
/
9
LCD
BIAS
has