Datasheet

PCF8536 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2012. All rights reserved.
Product data sheet Rev. 2 — 21 February 2012 28 of 74
NXP Semiconductors
PCF8536
Universal LCD low multiplex driver with 6 channel PWM generator
(6)
It should be noted that V
LCD
is sometimes referred to as the LCD operating voltage.
8.4.1 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 will be switched on or off, determine 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 14
. For a good contrast performance, the following rules should be followed:
(7)
(8)
V
on(RMS)
and V
off(RMS)
are properties of the display driver and are affected by the selection
of a, n (see Equation 4
to Equation 6) 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. V
th(off)
is sometimes just named V
th
. V
th(on)
is sometimes named saturation
voltage V
sat
.
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+
---------------------------==
Fig 14. Electro-optical characteristic: relative transmission curve of the liquid
V
on RMS
V
th on

V
off RMS
V
th off

V
RMS
[V]
100 %
90 %
10 %
OFF
SEGMENT
GREY
SEGMENT
ON
SEGMENT
V
th(off)
V
th(on)
Relative Transmission
013aaa494