PCF8562 datasheet(8/43 Pages) NXP

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PCF8562

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Product data sheet

Rev. 6 — 16 June 2011

8 of 43

NXP Semiconductors

PCF8562

Universal LCD driver for low multiplex rates

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

a segment. It can be thought of as a measurement of contrast.

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 1:

(1)

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)

Table 5.

Biasing characteristics

LCD drive

mode

Number of:

LCD bias

configuration

Backplanes Levels

static



1:2 multiplex

1⁄2

0.354

0.791

2.236

1:2 multiplex

1⁄3

0.333

0.745

2.236

1:3 multiplex

1⁄3

0.333

0.638

1.915

1:4 multiplex

1⁄3

0.333

0.577

1.732

off RMS



LCD

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

on RMS



LCD

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

on RMS



off RMS



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

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

on RMS





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

LCD

off RMS



–





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

LCD

on RMS



off RMS



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

–

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

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