PCF8537 datasheet(32/82 Pages) NXP

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PCF8537

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Product data sheet

Rev. 1 — 31 May 2012

32 of 82

NXP Semiconductors

PCF8537

Industrial LCD driver for multiplex rates up to 1:8

[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

power saving from 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), typically when the LCD exhibits approximately 10 % contrast. In

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

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 = 1 for static mode

n = 2 for 1:2 multiplex

n = 4 for 1:4 multiplex

n = 6 for 1:6 multiplex

n = 8 for 1:8 multiplex

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

Table 28.

LCD drive modes: summary of characteristics

LCD drive

mode

Number of:

LCD bias

configuration

[1]

VLCD[2]

Backplanes

Bias levels

static



Von(RMS)

1:2 multiplex

1⁄2

0.354

0.791

2.236

2.828Voff(RMS)

1:2 multiplex

1⁄3

0.333

0.745

2.236

3.0Voff(RMS)

1:2 multiplex[3]

1⁄4

0.395

0.729

1.845

2.529Voff(RMS)

1:4 multiplex[3]

1⁄2

0.433

0.661

1.527

2.309Voff(RMS)

1:4 multiplex

1⁄3

0.333

0.577

1.732

3.0Voff(RMS)

1:4 multiplex[3]

1⁄4

0.331

0.545

1.646

3.024Voff(RMS)

1:6 multiplex[3]

1⁄2

0.456

0.612

1.341

2.191Voff(RMS)

1:6 multiplex

1⁄3

0.333

0.509

1.527

3.0Voff(RMS)

1:6 multiplex

1⁄4

0.306

0.467

1.527

3.266Voff(RMS)

1:8 multiplex[3]

1⁄2

0.467

0.586

1.254

2.138Voff(RMS)

1:8 multiplex[3]

1⁄3

0.333

0.471

1.414

3.0Voff(RMS)

1:8 multiplex

1⁄4

0.293

0.424

1.447

3.411Voff(RMS)

off RMS



LCD

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

on RMS



LCD

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

on RMS



off RMS



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

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

on RMS





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

LCD

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