STE2002 datasheet(6/51 Pages) STMICROELECTRONICS

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STE2002

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CIRCUIT DESCRIPTION

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.

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, us-

ing 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 tem-

perature) 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).

Oscillator

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

play 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

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):

Figure 4. Bias level Generator

thus providing an 1/(n+4) ratio, with n calculated from:

For m = 81, n = 6 and an 1/10 ratio is set.

For m = 65, n =5 and an 1/9 ratio is set.

LC D

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

LC D ,

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

LC D ,

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

LC D ,

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

LC D ,VSS

VLCD

VSS

·VLCD

n + 3

n + 4

n + 2

n + 4

D00IN1150

–

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