PCF8545ATT datasheet(23/68 Pages) NXP

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NXP Semiconductors

PCF8545

Universal LCD driver for multiplex rates up to 1:8

7.4.1 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 gets 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 13. For a good contrast performance, the following rules should be followed:

(6)

(7)

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

selection of a, n (see Equation 3 to Equation 5) 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.

VRMS [V]

100 %

90 %

10 %

OFF

SEGMENT

GREY

SEGMENT

Vth(off)

Vth(on)

013aaa494

Figure 13. Electro-optical characteristic: relative transmission curve of the liquid

7.5 LCD drive mode waveforms

7.5.1 1:4 Multiplex drive mode

When four backplanes are provided in the LCD, the 1:4 multiplex drive mode applies,

as shown in Figure 14. This drawing is also showing the case of line inversion (see

Section 7.1.3.2).

PCF8545

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

Product data sheet

Rev. 2 — 4 October 2021

23 / 68

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