PCF8813 datasheet(36/72 Pages) PHILIPS

36 / 72 page

2004 Mar 05

Philips Semiconductors

Product speciﬁcation

(67 + 1)

× 102 pixels matrix LCD driver

PCF8813

11.11 Set HV generator stages

The PCF8813 incorporates a software-configurable

voltage multiplier. After reset (RES) the voltage multiplier

is set to 2

× VDD2. Other voltage multiplier factors are set

via the set HVgen stages command bits S[1:0].

11.12 Bias system

The bias voltage levels are set in the ratio of

R-R-nR-R-R giving a 1/(n + 4) bias system. Different

multiplex rates require different n factors. This is

programmed by BS[2:0] (see Table 15).

For multiplex rates of 1 : 68 the optimum bias value n is

given by:

resulting in 1/9 bias.

Changing the bias system from the optimum value will

have a consequence for the contrast and viewing angle.

One reason to depart from the optimum would be to

reduce the required operating voltage. A compromise

between contrast and operating voltage must be found for

any particular application.

Table 15 Bias system programming

Table 16 LCD bias voltage

Notes

1. Operation of bias level V4 is given for

V4 > VSS + 0.9 V. For higher multiplex rates, VLCD has

to be selected accordingly.

For multiplex rates equal to or lower than 1 : 24 (n = 2)

operation of the bias level V5 is limited to voltages

V5 < VDD2,3 − 1.1 V. VLCD has to be selected

accordingly.

The operating voltage can be set by software through the

interface. The binary number VOP representing the

operating voltage can be set according to the following

formula:

Where:

VOP is an 8-bit unsigned number used internally for

generation of the LCD supply voltage VLCD

VCAL is a 5-bit twos complement number set by the

module maker; see Table 17

VPR is an 8-bit unsigned number composed of PRS and

VPR* set by an interface command.

The corresponding voltage at the reference temperature,

TCUT, can be calculated as:

BS[2]

BS[1]

BS[0]

RECOMMENDED

MULTIPLEX RATES

0007

1 : 100

0016

1 : 80

1:65or1:67

0114

1 : 48

1:34or1:40

1012

1 : 24

1:18or1:16

1:10,1:9or1:8

n68

–

5.246

SYMBOL

BIAS VOLTAGES

BIAS

VOLTAGES

FOR 1/9 BIAS

VLCD

8/9 × VLCD

7/9 × VLCD

V4(1)

2/9 × VLCD

V5(2)

1/9 × VLCD

VSS

()

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

()

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

()

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

()

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

CAL 4:0

[] V

PR∗

LCD Tcut

()

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