PCF8548 datasheet(20/40 Pages) PHILIPS

20 / 40 page

1999 Aug 16

Philips Semiconductors

Product speciﬁcation

× 102 pixels matrix LCD driver

PCF8548

Table 4

Programming the required bias system

BS[2]

BS[1]

BS[0]

RECOMMENDED MUX RATE

0007

1 : 100

0016

1 : 81

0105

1 : 64

0114

1 : 49

1003

1 : 36

1012

1 : 24

1101

1 : 16

1110

1 : 9

Table 5

LCD bias voltage

12.10 Set VOP value

The voltage at reference temperature can be calculated

as: [VLCD (T = Tcut)]

(1)

The operating voltage VLCD can be set by software.

The generated voltage is dependent on the temperature,

programmed Temperature Coefficient (TC) and the

programmed voltage at reference temperature (Tcut).

(2)

SYMBOL

BIAS VOLTAGES

FOR 1

⁄9 BIAS

VLCD

(n + 3)/(n + 4)

⁄9 × VLCD

(n + 2)/(n + 4)

⁄9 × VLCD

2/(n + 4)

⁄9 × VLCD

1/(n + 4)

⁄9 × VLCD

VSS

LCD

Tcut

()

LCD

()

cut

–

() TC

[]

The parameters are explained in Fig.16 and Table 6.

The maximum voltage that can be generated is dependent

on the VDD2 voltage and the display load current.

Two overlapping VLCD ranges are selectable via the

command ‘HV-gen control’. For the LOW (PRS = 0) range

a=a1 and for the HIGH (PRS = 1) range a = a2 with steps

equal to b in both ranges. It should be noted that the

charge pump is turned off if VOP[6;0] and bit PRS are all set

to zero. For Mux 1 : 65 the optimum operation voltage of

the liquid can be calculated as follows:

where Vth is the threshold voltage of the liquid crystal

material used.

LCD

165

----------

–





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

6.85

Table 6

Typical values for parameters for the HV-generator programming

SYMBOL

BITS

VALUE

UNIT

2.94 (PRS = 0)

6.75 (PRS = 1)

0.03

Tcut

°C

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