PCF8536AT datasheet(44/103 Pages) NXP

44 / 103 page

PCA8530

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Product data sheet

Rev. 2 — 25 September 2014

44 of 103

NXP Semiconductors

PCA8530

Automotive 102 x 4 Chip-On-Glass LCD segment driver

8.10.5 LCD voltage selector

The LCD voltage selector co-ordinates the multiplexing of the LCD in accordance with the

selected LCD drive configuration. The operation of the voltage selector is controlled by the

Set-bias-mode command (see Table 16 on page 16) and the Set-MUX-mode command

(see Table 20 on page 20).

[1]

Determined from Equation 6.

[2]

Determined from Equation 5.

[3]

In this example, the discrimination factor and hence the contrast ratio is smaller. The advantage of this LCD drive mode is a power

saving from a reduction of VLCD.

Intermediate LCD biasing voltages are obtained from an internal voltage divider. The

biasing configurations that apply to the preferred modes of operation, together with the

biasing characteristics as functions of VLCD and the resulting discrimination ratios (D), are

given in Table 35. 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.

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. In

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

Bias is calculated by

, where the values for a are

a = 1 for 1⁄2 bias

a = 2 for 1⁄3 bias

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

(4)

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

The RMS off-state voltage (Voff(RMS)) for the LCD is calculated with Equation 5:

(5)

Table 35.

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

1⁄2

0.354

0.791

2.236

2.828

 V

off(RMS)

1:2 multiplex

1⁄3

0.333

0.745

2.236

3.0

 V

off(RMS)

1:4 multiplex[3]

1⁄2

0.433

0.661

1.527

2.309

 V

off(RMS)

1:4 multiplex

1⁄3

0.333

0.577

1.732

3.0

 V

off(RMS)

off RMS



LCD

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

on RMS



LCD

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

on RMS



off RMS



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

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

on RMS





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

LCD

off RMS



–





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

LCD

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