STE2002 Datasheet, PDF (6/51 Pages) STMicroelectronics – 81 X 128 SINGLE CHIP LCD CONTROLLER / DRIVER

STE2002
CIRCUIT DESCRIPTION
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.
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 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 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 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).
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 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
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, ⁿⁿ-----++-----³⁴-- V_LCD , ⁿⁿ-----++-----²⁴-- V_LCD ,n-----²_+-----4-- V_LCD, _n-----¹_+-----4-- V_LCD ,V_SS
Figure 4. Bias level Generator
R
V_LCD
n+3
n + 4 ^·VLCD
R
n+2
n + 4 ^·VLCD
nR
2
n + 4 ^·VLCD
R
1
n + 4 ^·VLCD
R
V_{SS D00IN1150}
thus providing an 1/(n+4) ratio, with n calculated from:
n= m – 3
For m = 81, n = 6 and an 1/10 ratio is set.
For m = 65, n =5 and an 1/9 ratio is set.
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