PCF8545ATTSLASHA datasheet(22/72 Pages) NXP

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PCF8545

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Product data sheet

Rev. 1 — 13 November 2013

22 of 72

NXP Semiconductors

PCF8545

Universal LCD driver for multiplex rates up to 1:8

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.

[1]

Determined from Equation 5.

[2]

Determined from Equation 4.

[3]

In these examples, the discrimination factor and hence the contrast ratios are smaller. The advantage of

these LCD drive modes is a reduction of the LCD voltage VLCD.

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.

Bias is calculated by

, where the values for a are

a = 1 for 1⁄2 bias

a = 2 for 1⁄3 bias

a = 3 for 1⁄4 bias

The RMS on-state voltage (Von(RMS)) for the LCD is calculated with Equation 3

(3)

where VLCD is the resultant voltage at the LCD segment and where the values for n are

n = 4 for 1:4 multiplex drive

n = 6 for 1:6 multiplex drive

n = 8 for 1:8 multiplex drive

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

(4)

Discrimination is the ratio of Von(RMS) to Voff(RMS) and is determined from Equation 5:

Table 23.

Preferred LCD drive modes: summary of characteristics

LCD multiplex

drive mode

Number of:

LCD bias

configuration

[1]

VLCD[2]

Backplanes

Levels

1:4 [3]

1⁄2

0.433

0.661

1.527

2.309Voff(RMS)

1:4

1⁄3

0.333

0.577

1.732

3.0Voff(RMS)

1:4 [3]

1⁄4

0.331

0.545

1.646

3.024Voff(RMS)

1:6 [3]

1⁄2

0.456

0.612

1.341

2.191Voff(RMS)

1:6

1⁄3

0.333

0.509

1.527

3.0Voff(RMS)

1:6

1⁄4

0.306

0.467

1.527

3.266Voff(RMS)

1:8 [3]

1⁄2

0.467

0.586

1.254

2.138Voff(RMS)

1:8 [3]

1⁄3

0.333

0.471

1.414

3.0Voff(RMS)

1:8

1⁄4

0.293

0.424

1.447

3.411Voff(RMS)

off RMS



LCD

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

on RMS



LCD

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

on RMS



off RMS



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

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

on RMS





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

LCD

off RMS



–





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

LCD

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