PCF8536AT datasheet(16/54 Pages) NXP

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PCA85233

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Product data sheet

Rev. 5 — 12 November 2018

16 of 54

NXP Semiconductors

PCA85233

Automotive 80 × 4 LCD driver for low multiplex rates

A practical value for VLCD is determined by equating Voff(RMS) with a defined LCD

threshold voltage (Vth(off)), typically when the LCD exhibits approximately 10 % contrast. In

the static drive mode a suitable choice is VLCD >3Vth(off).

Multiplex drive modes of 1:3 and 1:4 with 1⁄2 bias are possible but the discrimination and

hence the contrast ratios are smaller.

Bias is calculated by

, where the values for a are

a = 1 for 1⁄2 bias

a = 2 for 1⁄3 bias

The RMS on-state voltage (Von(RMS)) for the LCD is calculated with Equation 4:

(4)

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 5:

(5)

Discrimination is the ratio of Von(RMS) to Voff(RMS) and is determined from Equation 6:

(6)

Using Equation 6, 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.

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

on RMS





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

LCD

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



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