STE2002_06 Datasheet, PDF (8/61 Pages) STMicroelectronics – 81 x 128 single-chip LCD controller/driver

Circuit description
2
Circuit description
STE2002
2.1
Supplies voltages and grounds
V_DD2 is supply voltages to the internal voltage generator (see below). If the internal voltage
generator is not used, this should be connected to V_DD1 pad. V_DD1 supplies the rest of the
IC. V_DD1 supply voltage could be different form V_DD2.
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 V_LCD voltage. The output voltage (V_LCDOUT) is tightly controlled through the
V_LCDSENSE 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 V_LCDIN and V_LCDOUT pads must be connected together. An external supply could
be connected to V_LCDIN to supply the LCD without using the internal generator. In such
event the V_LDCOUT and V_LCDSENSE 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 V_DD1 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):
V_LCD,
n_-----+-----3_--
n+4
V_L
CD^,
n_-----+-----2_--
n+4
V_L
CD^,
-----²-------
n+4
V
LCD
,
-----¹-------
n+4
V_LCD,V_SS
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