STE2002 datasheet(8/61 Pages) STMICROELECTRONICS

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Circuit description

STE2002

8/61

Circuit description

2.1

Supplies voltages and grounds

VDD2 is supply voltages to the internal voltage generator (see below). If the internal voltage

generator is not used, this should be connected to VDD1 pad. VDD1 supplies the rest of the

IC. VDD1 supply voltage could be different form VDD2.

2.2

Internal supply voltage generator

The IC has a fully integrated (no external capacitors required) charge pump for the Liquid

Crystal Display supply voltage generation. The multiplying factor can be programmed to be:

Auto, X6, X5, X4, X3, X2, using the ’set CP Multiplication’ Command. If Auto is set, the

multiplying factor is automatically selected to have the lowest current consumption in every

condition. This make possible to have an input voltage that changes over time and a

constant VLCD voltage. The output voltage (VLCDOUT) is tightly controlled through the

VLCDSENSE pad. For this voltage, eight different temperature coefficients (TC, rate of change

with temperature) can be programmed using the bits TC1 and TC0 and T2,T1 & T0. This will

ensure no contrast degradation over the LCD operating range. Using the internal charge

pump, the VLCDIN and VLCDOUT pads must be connected together. An external supply could

be connected to VLCDIN to supply the LCD without using the internal generator. In such

event the VLDCOUT and VLCDSENSE must be connected to GND and the internal voltage

generator must be programmed to zero (PRS = [0;0], Vop = 0 - Reset condition).

2.3

Oscillator

A fully integrated oscillator (requires no external components) is present to provide the clock

for the Display System. When used the OSC pad must be connected to VDD1 pad. An

external oscillator could be used and fed into the OSC pin. An oscillator out is provided on

the OSCOUT Pad to cascade two or more drivers

2.4

Bias levels

To properly drive the LCD, six (Including VLCD and VSS) different voltage (Bias) levels are

generated. The ratios among these levels and VLCD, should be selected according to the

MUX ratio (m). They are established to be (Fig. 4):

LCD

------------- V

LCD,

------------- V

LCD,

------------- V

LCD,

------------- V

LCD,VSS

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