PCF8531 Ver la hoja de datos (PDF) - Philips Electronics

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PCF8531

34 × 128 pixel matrix driver

Philips Electronics 

Philips Semiconductors

34 × 128 pixel matrix driver

Product specification

PCF8531

8.18.8 LCD BIAS VOLTAGE

Table 3 Intermediate LCD bias voltages

SYMBOL

BIAS

VOLTAGES

EXAMPLE FOR

1⁄7 BIAS

V1

VLCD

VLCD

V2

nn-----++-----34-- × VLCD

6⁄7 × VLCD

V3

nn-----++-----24-- × VLCD

5⁄7 × VLCD

V4

n-----+2-----4-- × VLCD

2⁄7 × VLCD

V5

n-----+1-----4-- × VLCD

1⁄7 × VLCD

V6

VSS

VSS

8.18.9 SET VOP VALUE:

The operating voltage VLCD can be set by software.

The voltage at reference temperature [VLCD (T = Tcut)] can

be calculated as: VLCD (Tcut) = (a + VOP × b).

The generated voltage is dependent on the temperature,

programmed Temperature Coefficient (TC) and the

programmed voltage at reference temperature (Tcut).

VLCD = VLCD (Tcut) × [1 + TC × (T − Tcut)].

The parameter values are given in Table 4.

Two overlapping VLCD ranges can be selected via the

command ‘HV-gen control’ (see Table 4 and Fig.8).

The maximum voltage that can be generated depends on

the VDD2 and VDD3 voltages and the display load current.

For Mux 1 : 34, the optimum operating voltage of the liquid

can be calculated as:

VLCD

=

----------1-----+---------3---4------------

2

×





1

–

----1-3---4--

×

Vt

h

=

5.30 × Vth

Where Vth is the threshold voltage of the liquid crystal

material used.

The practical value for VOP is determined by equating

Voff(rms) with a defined LCD threshold voltage (Vth),

typically when the LCD exhibits approximately

10% contrast.

As the programming range for the internally generated

VLCD allows values above the maximum allowed VLCD, the

user has to ensure, while setting the VOP register and

selecting the temperature compensation, that the VLCD

limit of maximum 9 V will never be exceeded under all

conditions and including all tolerances.

Table 4 Parameter values for the HV generator programming

SYMBOL

Tcut

a

b

Programming range

VALUE

PRS = 0

27

2.94

0.03

2.94 to 6.75

PRS = 1

27

6.75

0.03

6.75 to 10.56

UNIT

°C

V

V

V

2000 Feb 11

14

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