PCA9620 datasheet(21/71 Pages) NXP

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PCA9620

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Product data sheet

Rev. 1 — 9 December 2010

21 of 71

NXP Semiconductors

PCA9620

Universal LCD driver for low multiplex rates

[1]

Determined from Equation 3.

[2]

Determined from Equation 2.

[3]

In this 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 1:

(1)

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 2:

Table 26.

LCD drive modes: summary of characteristics

LCD drive

mode

Number of:

LCD bias

configuration

[1]

VLCD[2]

Backplanes Levels

static

∞

Von(RMS)

1:2 multiplex

⁄

0.354

0.791

2.236

2.828

× V

off(RMS)

1:2 multiplex

⁄

0.333

0.745

2.236

3.0

× V

off(RMS)

1:2 multiplex[3]

⁄

0.395

0.729

1.845

2.529

× V

off(RMS)

1:4 multiplex[3]

⁄

0.433

0.661

1.527

2.309

× V

off(RMS)

1:4 multiplex

⁄

0.333

0.577

1.732

3.0

× V

off(RMS)

1:4 multiplex[3]

⁄

0.331

0.545

1.646

3.024

× V

off(RMS)

1:6 multiplex[3]

⁄

0.456

0.612

1.341

2.191

× V

off(RMS)

1:6 multiplex

⁄

0.333

0.509

1.527

3.0

× V

off(RMS)

1:6 multiplex

⁄

0.306

0.467

1.527

3.266

× V

off(RMS)

1:8 multiplex[3]

⁄

0.467

0.586

1.254

2.138

× V

off(RMS)

1:8 multiplex[3]

⁄

0.333

0.471

1.414

3.0

× V

off(RMS)

1:8 multiplex

⁄

0.293

0.424

1.447

3.411

× V

off(RMS)

off RMS

()

LCD

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

on RMS

()

LCD

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

on RMS

()

off RMS

()

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

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

on RMS

()

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

LCD

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