PCF8545ATTAY datasheet(22/68 Pages) NXP

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NXP Semiconductors

PCF8545

Universal LCD driver for multiplex rates up to 1:8

Number of:

LCD multiplex

drive mode

Backplanes

Levels

LCD bias

configuration

[1] VLCD

[2]

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)

Table 22. Preferred LCD drive modes: summary of characteristics

[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:

(5)

VLCD is sometimes referred to as the LCD operating voltage.

PCF8545

All information provided in this document is subject to legal disclaimers.

Product data sheet

Rev. 2 — 4 October 2021

22 / 68

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