Product data

PCF8534A All information provided in this document is subject to legal disclaimers. © NXP B.V. 2011. All rights reserved.
Product data sheet Rev. 6 — 25 July 2011 10 of 52
NXP Semiconductors
PCF8534A
Universal LCD driver for low multiplex rates
(3)
Using Equation 3
, the discrimination for an LCD drive mode of 1:3 multiplex with
1
⁄
2
bias is and the discrimination for an LCD drive mode of 1:4 multiplex with
1
⁄
2
bias is .
The advantage of these LCD drive modes is a reduction of the LCD full scale voltage V
LCD
as follows:
• 1:3 multiplex (
1
⁄
2
bias):
• 1:4 multiplex (
1
⁄
2
bias):
These compare with when
1
⁄
3
bias is used.
V
LCD
is sometimes referred as the LCD operating voltage.
7.3.1 Electro-optical performance
Suitable values for V
on(RMS)
and V
off(RMS)
are dependent on the LCD liquid used. The
RMS voltage, at which a pixel is switched on or off, determines the transmissibility of the
pixel.
For any given liquid, there are two threshold values defined. One point is at 10 % relative
transmission (at V
th(off)
) and the other at 90 % relative transmission (at V
th(on)
), see
Figure 6
. For a good contrast performance, the following rules should be followed:
(4)
(5)
V
on(RMS)
and V
off(RMS)
are properties of the display driver and are affected by the selection
of a, n (see Equation 1
to Equation 3) and the V
LCD
voltage.
V
th(off)
and V
th(on)
are properties of the LCD liquid and can be provided by the module
manufacturer.
It is important to match the module properties to those of the driver in order to achieve
optimum performance.
D
V
on RMS
V
off RMS
-----------------------
a
2
2a n++
a
2
2a– n+
---------------------------==
3 1.732=
21
3
---------- 1.528=
V
LCD
6V
off RMS
 2.449V
off RMS
==
V
LCD
43
3
----------------------
2.309V
off RMS
==
V
LCD
3V
off RMS
=
V
on RMS
V
th on

V
off RMS
V
th off
