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 k to 1 M When using an external

resistor divider, the VLCD 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-VLCD

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 VLCD input.

Figure 193. Bias Generation
0
1
VLCDEXT
0
0
LCD Off
Internal VLCD
LCDREF/R13
R23
R03
LCDCAP/R33
REXT
1
0
1
0
1
0
1
0V5
V4 int.
V3 int.
V2 int.
VLCD
AVCC
LCD2B
0
VLCDx > 0
VLCDREFx > 0
R03EXT
Charge
Pump
DVCC
R
R
R
R
R
Rx Rx
Rx
Static 1/2 Bias1/3 Bias
Optional External Resistors
Rx = Optional Contrast Control
V1 (VLCD)
V2 (2/3 VLCD)
V3 (1/2 VLCD)
V4 (1/3 VLCD)