PCF2113EU2 datasheet(9/72 Pages) PHILIPS

9 / 72 page

2001 Dec 19

Philips Semiconductors

Product speciﬁcation

LCD controllers/drivers

PCF2113x

FUNCTIONAL DESCRIPTION

7.1

LCD supply voltage generator

The LCD supply voltage may be generated on-chip. The

VLCD generator is controlled by two internal 6-bit registers:

VA and VB. The nominal LCD operating voltage at room

temperature is given by the relationship:

VOP(nom) = (integer value of register × 0.08) + 1.82

7.1.1

PROGRAMMING RANGES

Programmed value: 1 to 63. Voltage: 1.90 to 6.86 V.

Tref =27 °C.

Values producing more than 6.5 V at operating

temperature are not allowed. Operation above this

voltage may damage the device. When programming the

operating voltage the VLCD tolerance and temperature

coefficient must be taken into account.

Values below 2.2 V are below the specified operating

range of the chip and are therefore not allowed.

Value 0 for VA and VB switches the generator off

(i.e. VA = 0 in character mode, VB = 0 in icon mode).

Usually register VA is programmed with the voltage for

character mode and register VB with the voltage for icon

mode.

When VLCD is generated on-chip the VLCD pins should be

decoupled to VSS with a suitable capacitor.

The generated VLCD is independent of VDD and is

temperature compensated. When the VLCD generator and

the direct mode are switched off, an external voltage may

be supplied at connected pins VLCD1 and VLCD2.VLCD1 and

VLCD2 may be higher or lower than VDD2.

During direct mode (program DM register bit) the internal

VLCD generator is turned off and the VLCD2 output voltage

is directly connected to VDD2. This reduces the current

consumption during icon mode and Mux 1 : 9 (depending

on VDD2 value and LCD liquid properties).

The VLCD generator ensures that, as long as VDD is in the

valid range (2.2 to 4 V), the required peak voltage

VOP = 6.5 V can be generated at any time.

7.2

LCD bias voltage generator

The intermediate bias voltages for the LCD display are

also generated on-chip. This removes the need for an

external resistive bias chain and significantly reduces the

system current consumption. The optimum value of VLCD

depends on the multiplex rate, the LCD threshold voltage

(Vth) and the number of bias levels. Using a 5-level bias

scheme for 1 : 18 maximum rate allows VLCD < 5 V for

most LCD liquids. The intermediate bias levels for the

different multiplex rates are shown in Table 1. These bias

levels are automatically set to the given values when

switching to the corresponding multiplex rate.

Table 1

Bias levels as a function of multiplex rate; note 1

Note

1. The values in the table are given relative to VLCD − VSS, e.g. 3/4 means 3/4 × (VLCD − VSS).

MULTIPLEX

RATE

NUMBER

OF LEVELS

1:18

VLCD

3/4

1/2

1/4

VSS

1:9

VLCD

3/4

1/2

1/4

VSS

1:2

VLCD

2/3

1/3

VSS

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