PCF8535 datasheet(13/52 Pages) PHILIPS

13 / 52 page

1999 Aug 24

Philips Semiconductors

Objective speciﬁcation

× 133 pixel matrix driver

PCF8535

handbook, halfpage

MGS473

VLCD

°C

Fig.4 VLCD as function of liquid crystal temperature (typical values).

Table 5

Selectable temperature coefﬁcients

7.13

VOP

7.13.1

SET VOP VALUE

The voltage at the reference temperature can be

calculated as: [VLCD (T=Tcut)]

(4)

The operating voltage, VOP, can be set by software.

The generated voltage is dependent on the temperature,

programmed Temperature Coefficient (TC) and the

programmed voltage at the reference temperature (Tcut):

(5)

The values for Tcut, a and b are given in Table 6.

The maximum voltage that can be generated is dependent

on the voltage VDD2 and the display load current.

Two overlapping VOP ranges are selectable via the

command page “Hv-gen control”, see Fig.5.

The low range offers programming from 4.5 to 10.215 V,

with the high range from 10.215 to 15.93 V at the cut point

temperature, Tcut. Care must be taken, when using

temperature coefficients, that the programmed voltage

does not exceed the maximum allowed VLCD voltage,

see Chapter 10.

For a particular liquid, the optimum VLCD can be calculated

for a given multiplex rate. For a Mux rate of 1 : 65, the

optimum operating voltage of the liquid can be calculated

as:

(6)

where Vth is the threshold voltage of the liquid crystal

material used.

Table 6

Values for parameters of the HV generator

programming

TC[2]

TC[1]

TC[0]

TC VALUE

UNIT

000

°C

001

−0.44 × 10−3

°C

010

−1.10 × 10−3

°C

011

−1.45 × 10−3

°C

100

−1.91 × 10−3

°C

101

−2.15 × 10−3

°C

110

−2.32 × 10−3

°C

111

−2.74 × 10−3

°C

LCD

Tcut

()

LCD

()

cut

–

() TC

()

SYMBOL

BITS

VALUE

UNIT

PRS = 0

4.5

PRS = 1

10.215

0.045

Tcut

°C

LCD

165

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–





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6.85

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