PCF8566P datasheet(7/40 Pages) PHILIPS

7 / 40 page

1998 May 04

Philips Semiconductors

Product speciﬁcation

Universal LCD driver for low multiplex

rates

PCF8566

6.1

Power-on reset

At power-on the PCF8566 resets to a defined starting

condition as follows:

1. All backplane outputs are set to VDD

2. All segment outputs are set to VDD

3. The drive mode ‘1 : 4 multiplex with 1

⁄3bias’ is selected

4. Blinking is switched off

5. Input and output bank selectors are reset (as defined

in Table 5)

6. The I2C-bus interface is initialized

7. The data pointer and the subaddress counter are

cleared.

Data transfers on the I2C-bus should be avoided for 1 ms

following power-on to allow completion of the reset action.

6.2

LCD bias generator

The full-scale LCD voltage (Vop) is obtained from

VDD − VLCD. The LCD voltage may be temperature

compensated externally through the VLCD supply to pin 12.

Fractional LCD biasing voltages are obtained from an

internal voltage divider of three series resistors connected

between VDD and VLCD. The centre resistor can be

switched out of circuit to provide a 1

⁄2bias voltage level for

the 1 : 2 multiplex configuration.

6.3

LCD voltage selector

The LCD voltage selector coordinates the multiplexing of

the LCD according to the selected LCD drive

configuration. The operation of the voltage selector is

controlled by MODE SET commands from the command

decoder. The biasing configurations that apply to the

preferred modes of operation, together with the biasing

characteristics as functions of Vop =VDD − VLCD and the

resulting discrimination ratios (D), are given in Table 2.

A practical value of Vop 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 Vop ≥ 3Vth. Multiplex drive

ratios of 1 : 3 and 1 : 4 with 1

⁄2 bias are possible but the

discrimination and hence the contrast ratios are smaller

(

for 1 : 3 multiplex or

for

1 : 4 multiplex). The advantage of these modes is a

reduction of the LCD full scale voltage Vop as follows:

1 : 3 multiplex (1

⁄2bias):

1 : 4 multiplex (1

⁄2bias):

These compare with Vop =3Voff(rms) when 1⁄3bias is used.

1.732

21 3

⁄

1.528

op(mrs)

2.449V

off rms

()

⁄ V

off rms

()

2.309V

off rms

()

Table 2

Preferred LCD drive modes: summary of characteristics

LCD DRIVE MODE

LCD BIAS

CONFIGURATION

Static (1 BP)

static (2 levels)

∞

1 : 2 MUX (2 BP)

⁄2 (3 levels)

1 : 2 MUX (2 BP)

⁄3 (4 levels)

⁄3 = 0.333

1 : 3 MUX (3 BP)

⁄3 (4 levels)

⁄3 = 0.333

1 : 4 MUX (4 BP)

⁄3 (4 levels)

⁄3 = 0.333

off rms

()

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

on rms

()

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

on rms

()

off rms

()

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

2 4

0.354

⁄

10 4

⁄

0.791

52.236

⁄

0.745

52.236

33 9

⁄

0.638

33 3

⁄

1.915

⁄

0.577

31.732

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