PCF8553DTTSLASHA datasheet(16/51 Pages) NXP

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NXP Semiconductors

PCF8553

40 × 4 LCD segment driver

Discrimination is a term which is defined as the ratio of the on and off RMS voltages

(Von(RMS) to Voff(RMS)) across a segment. It can be thought of as a measurement of

contrast. Discrimination is determined from Equation 5:

(5)

Using Equation 5, the discrimination for an LCD drive mode of 1:3 multiplex with 1⁄2 bias

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

VLCD as follows:

• 1:3 multiplex (1⁄2 bias):

•

1:4 multiplex (1⁄2 bias):

These compare with

when 1⁄3 bias is used.

VLCD is sometimes referred as the LCD operating voltage.

8.2.1 Electro-optical performance

Suitable values for Von(RMS) and Voff(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 Vth(off)) and the other at 90 % relative transmission (at Vth(on)), see

Figure 9. For a good contrast performance, the following rules should be followed:

(6)

(7)

Von(RMS) (see Equation 3) and Voff(RMS) (see Equation 5) are properties of the display

driver and are affected by the selection of abias, nMUX, and the VLCD voltage.

Vth(off) and Vth(on) are properties of the LCD liquid and can be provided by the module

manufacturer. Vth(off) is sometimes named Vth. Vth(on) is sometimes named saturation

voltage Vsat.

It is important to match the module properties to those of the driver in order to achieve

optimum performance.

PCF8553

All information provided in this document is subject to legal disclaimers.

Product data sheet

Rev. 4 — 20 April 2021

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