PCF8532 datasheet(8/49 Pages) NXP

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PCF8532

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Product data sheet

Rev. 2 — 10 February 2011

8 of 49

NXP Semiconductors

PCF8532

Universal LCD driver for low multiplex rates

Discrimination is the ratio of Von(RMS) to Voff(RMS) and is determined from Equation 3:

(3)

Using Equation 3, the discrimination for an LCD drive mode of 1:3 multiplex with

⁄

2 bias is

and the discrimination for an LCD drive mode of 1:4 multiplex with

⁄

2 bias is

The advantage of these LCD drive modes is a reduction of the LCD full scale voltage VLCD

as follows:

• 1:3 multiplex (1⁄2 bias):

• 1:4 multiplex (1⁄2 bias):

These compare with

when 1

⁄

3 bias is used.

It should be noted that VLCD is sometimes referred as the LCD operating voltage.

7.3.1 Electro-optical performance

Suitable values for Von(RMS) and Voff(RMS) are dependant 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 Vlow) and the other at 90% relative transmission (at Vhigh), see Figure 5.

For a good contrast performance, the following rules should be followed:

(4)

(5)

Von(RMS) and Voff(RMS) are properties of the display driver and are affected by the selection

of a, n (see Equation 1 to Equation 3) and the VLCD voltage.

Vlow and Vhigh 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.

on RMS

()

off RMS

()

-----------------------

()

–

()

–

()

–

()

--------------------------------------------

1.732

----------

1.528

LCD

off RMS

()

2.449V

off RMS

()

LCD

()

----------------------

2.309V

off RMS

()

LCD

off RMS

()

on RMS

()

high

≥

off RMS

()

low

≤

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