PCF8534A datasheet(7/44 Pages) NXP

7 / 44 page

PCF8534A_3

Product data sheet

Rev. 03 — 10 November 2008

7 of 44

NXP Semiconductors

PCF8534A

Universal LCD driver for low multiplex rates

Table 5 shows the biasing conﬁgurations applicable to the preferred operating modes

together with the biasing characteristics as functions of Voper and the resulting

discrimination ratios (D).

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

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

the static drive mode a suitable choice is Voper > 3Vth.

Multiplex drive ratios of 1:3 and 1:4 with 1

⁄

2 bias are possible but the discrimination and

hence the contrast ratios are smaller e.g.:

for 1:3 multiplex or

for 1:4 multiplex

The advantage of these modes is the reduction of the LCD full-scale voltage Voper as

follows:

• 1:3 multiplex (1

⁄2 bias):

• 1:4 multiplex (1

⁄2 bias):

These compare with Voper =3Voff(RMS) when 1⁄3 bias is used. It should be noted that

Voper =VLCD.

Table 5.

Preferred LCD drive modes: summary of characteristics

LCD drive

mode

Number of

LCD bias

conﬁguration

Backplanes

Levels

static

∞

1:2

⁄

0.354

0.791

2.234

1:2

⁄

0.333

0.745

2.237

1:3

⁄

0.333

0.638

1.915

1:4

⁄

0.333

0.577

1.732

----------

1.528





oper

off RMS

()

2.449V

off RMS

()

oper

()

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

2.309V

off RMS

()

off RMS

()

oper

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

on RMS

()

oper

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

on RMS

()

off RMS

()

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

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