PCA9620 datasheet(22/71 Pages) NXP

22 / 71 page

PCA9620

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Product data sheet

Rev. 1 — 9 December 2010

22 of 71

NXP Semiconductors

PCA9620

Universal LCD driver for low multiplex rates

(2)

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

(3)

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

7.4.1.1

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 14.

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.

off RMS

()

–

()

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

LCD

on RMS

()

off RMS

()

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

()

–

()

–

()

–

()

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

Fig 14. Electro-optical characteristic: relative transmission curve of the liquid

on RMS

()

high

≥

off RMS

()

low

≤

VRMS [V]

100 %

90 %

10 %

OFF

SEGMENT

GREY

SEGMENT

Vlow

Vhigh

001aam358

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