pcf8576d NXP Semiconductors, pcf8576d Datasheet - Page 10

• Manufacturer Part Number: pcf8576d
• Description: Universal Lcd Driver For Low Multiplex Rates
• Manufacturer: NXP Semiconductors

Philips Semiconductors
6.1
At power-on the PCF8576D resets to the following starting
conditions:
Data transfers on the I
following power-on to allow completion of the reset action.
6.2
Fractional LCD biasing voltages are obtained from an
internal voltage divider comprising three resistors
connected in series between V
resistor can be bypassed to provide a
for the 1 : 2 multiplex configuration. The LCD voltage can
be temperature compensated externally via the supply to
pin V
6.3
The LCD voltage selector co-ordinates the multiplexing of
the LCD in accordance with 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
Discrimination ratios (D), are given in Table 2.
A practical value for V
V
typically when the LCD exhibits approximately 10%
contrast. In the static drive mode a suitable choice is
V
Multiplex drive modes of 1 : 3 and 1 : 4 with
possible but the discrimination and hence the contrast
ratios are smaller.
2004 Dec 22
off(rms)
LCD
All backplane outputs are set to V
All segment outputs are set to V
Drive mode ‘1 : 4 multiplex with
Blinking is switched off
Input and output bank selectors are reset (as defined in
Table 4)
The I
The data pointer and the subaddress counter are
cleared
Display is disabled.
Universal LCD driver for low
multiplex rates
LCD
> 3V
Power-on reset
LCD bias generator
LCD voltage selector
2
with a defined LCD threshold voltage (V
C-bus interface is initialized
.
th
.
LCD
2
C-bus should be avoided for 1 ms
is determined by equating
LCD
LCD
1
LCD
and V
3
and the resulting
LCD
bias’ is selected
1
2
bias voltage level
SS
. The middle
1
2
bias are
th
),
10
6.3.1
Bias is calculated by the formula
For
The LCD on voltage (V
The LCD off voltage (V
where V
is the LCD drive mode: 1 = static, 2 = 1 : 2, 3 = 1 : 3,
4 = 1 : 4.
Discrimination is the ratio of V
by the formula
Using the above formula, the discrimination for an LCD
drive mode of 1 : 3 with
discrimination for an LCD drive mode of 1 : 4 with
is
The advantage of these LCD drive modes is a reduction of
the LCD full-scale voltage V
1 : 3 multiplex (
V
1 : 4 multiplex (
V
These compare with V
used.
V
V
op
op
LCD
LCD
----------
--- -
N
------------------------------------------------------------
a
--------------------------------- -
1
3
1
21
N
2
2
=
=
+
–
bias, a = 1; for
= 1.528.
op
LCD
1
--------------------- -
2a
6 V
N 1
4
is the resultant voltage at the LCD segment; N
+
–
+
3
a
BIAS FORMULAE
N
off(rms)
N
2
V
---------
V
1
1
3
2
2
on
off
bias):
bias):
------------ -
1
= 2.309 V
=
1
+
= 2.449 V
1
a
LCD
on
off
3
1
-------------------------------------------- -
bias, a = 2.
) is calculated by the formula
) is calculated by the formula
a
a 1
2
2
= 3 V
bias is
+
–
LCD
1
on
off(rms)
2
2
off(rms)
as follows:
off(rms)
to V
+
+
------------ -
1
1
+
N 1
N 1
3
off
Product specification
a
–
–
, and is determined
= 1.732, and the
PCF8576D
when
1
3
bias is
1
2
bias