PCF8534AHL(2011) データシートの表示（PDF） - NXP Semiconductors.

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PCF8534AHL
(Rev.:2011)

Universal LCD driver for low multiplex rates

NXP Semiconductors. 

NXP Semiconductors

PCF8534A

Universal LCD driver for low multiplex rates

D

=

-V----o---n----R---M----S---

VoffRMS

=

a----2---+-----2----a----+-----n--

a2 – 2a + n

(3)

Using Equation 3, the discrimination for an LCD drive mode of 1:3 multiplex with

1⁄2 bias is 3 = 1.732 and the discrimination for an LCD drive mode of 1:4 multiplex with

1⁄2 bias is

-----2---1--

3

=

1.528 .

The advantage of these LCD drive modes is a reduction of the LCD full scale voltage VLCD

as follows:

• 1:3 multiplex (1⁄2 bias): VLCD = 6  VoffRMS = 2.449VoffRMS

• 1:4 multiplex (1⁄2 bias): VLCD =

---4--------------3----

3

= 2.309VoffRMS

These compare with VLCD = 3VoffRMS when 1⁄3 bias is used.

VLCD is sometimes referred as the LCD operating voltage.

7.3.1 Electro-optical performance

Suitable values for Von(RMS) and Voff(RMS) are dependent on the LCD liquid used. The

RMS voltage, at which a pixel is switched on or off, determines the transmissibility of the

pixel.

For any given liquid, there are two threshold values defined. One point is at 10 % relative

transmission (at Vth(off)) and the other at 90 % relative transmission (at Vth(on)), see

Figure 6. For a good contrast performance, the following rules should be followed:

VonRMS  Vthon

(4)

VoffRMS  Vthoff

(5)

Von(RMS) and Voff(RMS) are properties of the display driver and are affected by the selection

of a, n (see Equation 1 to Equation 3) and the VLCD voltage.

Vth(off) and Vth(on) are properties of the LCD liquid and can be provided by the module

manufacturer.

It is important to match the module properties to those of the driver in order to achieve

optimum performance.

PCF8534A

Product data sheet

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

Rev. 6 — 25 July 2011

© NXP B.V. 2011. All rights reserved.

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