PCF8536AT datasheet(19/54 Pages) NXP

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PCA8576F

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Product data sheet

Rev. 3 — 3 December 2014

19 of 54

NXP Semiconductors

PCA8576F

Automotive 40 × 4 LCD driver

where the values for n are

n = 1 for static drive mode

n = 2 for 1:2 multiplex drive mode

n = 3 for 1:3 multiplex drive mode

n = 4 for 1:4 multiplex drive mode

The RMS off-state voltage (Voff(RMS)) for the LCD is calculated with Equation 2:

(2)

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

1⁄2 bias is

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.

7.6.2.1

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 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.

off RMS



–





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

LCD

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



th on





off RMS



th off





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