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LCD_A Controller Operation
19-6 LCD_A Controller
To source the bias voltages V2 − V4 externally, REXT is set. This also disables
the internal bias generation. Typically an equally weighted resistor divider is
used with resistors ranging from 100 kW to 1 MW. When using an external
resistor divider, the V
LCD
voltage may be sourced from the internal charge
pump when VLCDEXT = 0. V5 can also be sourced externally when R03EXT
is set.
When using an external resistor divider R33 may serve as a switched-V
LCD
output when VLCDEXT = 0. This allows the power to the resistor ladder to be
turned off eliminating current consumption when the LCD is not used. When
VLCDEXT = 1, R33 serves as a V
LCD
input.
Figure 19−3. Bias Generation
0
1
VLCDEXT
0
0
LCD Off
Internal V
LCD
LCDREF/R13
R23
R03
LCDCAP/R33
REXT
1
0
1
0
1
0
1
0
V5
V4 int.
V3 int.
V2 int.
V
LCD
AV
CC
LCD2B
0
VLCDx > 0
VLCDREFx > 0
R03EXT
Charge
Pump
DV
CC
R
R
R
R
R
Rx
Rx
Rx
Static 1/2 Bias 1/3 Bias
Optional External Resistors
Rx = Optional Contrast Control
V1 (V
LCD
)
V2 (2/3 V
LCD
)
V3 (1/2 V
LCD
)
V4 (1/3 V
LCD
)