OM4085 Philips Semiconductors, OM4085 Datasheet - Page 6

• Manufacturer Part Number: OM4085
• Description: Universal LCD driver for low multiplex rates
• Manufacturer: Philips Semiconductors

Philips Semiconductors
Power-on reset
At power-on the OM4085 resets to a defined starting
condition as follows:
1. All backplane outputs are set to V
2. All segment outputs are set to V
3. The drive mode ‘1 : 4 multiplex with
4. Blinking is switched off
5. Input and output bank selectors are reset (as defined
6. The I
7. The data pointer and the subaddress counter are
Data transfers on the I
following power-on to allow completion of the reset action.
LCD bias generator
The full-scale LCD voltage (V
V
compensated externally through the V
Fractional LCD biasing voltages are obtained from an
internal voltage divider of three series resistors connected
between V
switched out of circuit to provide a
the 1 : 2 multiplex configuration.
Table 2
1997 Feb 25
Static (1 BP)
1 : 2 MUX (2 BP)
1 : 2 MUX (2 BP)
1 : 3 MUX (3 BP)
1 : 4 MUX (4 BP)
DD
LCD DRIVE MODE
Universal LCD driver for low multiplex
rates
in Table 5)
cleared.
V
LCD
2
C-bus interface is initialized
Preferred LCD drive modes: summary of characteristics
DD
. The LCD voltage may be temperature
and V
LCD
2
. The centre resistor can be
C-bus should be avoided for 1 ms
CONFIGURATION
static (2 levels)
op
1
1
1
1
LCD BIAS
2
3
3
3
) is obtained from
(3 levels)
(4 levels)
(4 levels)
(4 levels)
1
2
DD
bias voltage level for
LCD
DD
1
3
supply to pin 12.
bias’ is selected
2 4
1
1
1
V
---------------------- -
3
3
3
off rms
= 0.333
= 0.333
= 0.333
V
=
0
6
op
0.354
LCD voltage selector
The LCD voltage selector coordinates the multiplexing of
the LCD according to the selected LCD drive
configuration. The operation of the voltage selector is
controlled by MODE SET commands from the command
decoder. The biasing configurations that apply to the
preferred modes of operation, together with the biasing
characteristics as functions of V
resulting discrimination ratios (D), are given in Table 2.
A practical value of V
with a defined LCD threshold voltage (V
the LCD exhibits approximately 10% contrast. In the static
drive mode a suitable choice is V
ratios of 1 : 3 and 1 : 4 with
discrimination and hence the contrast ratios are smaller
(
1 : 4 multiplex). The advantage of these modes is a
reduction of the LCD full scale voltage V
1 : 3 multiplex (
1 : 4 multiplex (
These compare with V
V
V
op
op
3
=
=
=
1.732
4
6V
3
op(mrs)
3V
for 1 : 3 multiplex or
off rms
1
1
10 4
33 9
5 3
3 3
2
2
V
---------------------- -
bias):
bias):
=
on rms
V
2.449V
op
=
=
1
op
=
=
op
is determined by equating V
=
0.745
0.577
0.791
0.638
= 3 V
2.309V
1
off rms
2
off(rms)
bias are possible but the
op
op
off rms
= V
21 3
Product specification
3 V
when
DD
D
33 3
th
th
op
), typically when
=
5
5
3
. Multiplex drive
OM4085
V
as follows:
1
=
V
---------------------- -
V
=
=
=
3
LCD
off rms
bias is used.
on rms
1.528
=
2.236
2.236
1.732
1.915
and the
off(rms)
for