LCD_C Operation
939
SLAU367P – October 2012 – Revised April 2020
Copyright © 2012–2020, Texas Instruments Incorporated
LCD_C Controller
To source the bias voltages V2 to V4 externally, LCDEXTBIAS is set. This also disables the internal bias
generation. Typically, an equally weighted resistor divider is used with resistors ranging from a few k
Ω
to
1 M
Ω
, depending on the size of the display. When using an external resistor divider, the V
LCD
voltage may
be sourced from the internal charge pump when VLCDEXT = 0 taking the maximum charge pump load
current into account. V5 can also be sourced externally when R03EXT = 1. In static mode and all mux
modes using 1/2 biasing or 1/3 biasing, when R03EXT = 1 V5 can control the contrast of the connected
display by changing the voltage at the low end of the external resistor divider Rx as shown in the left part
of
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, which eliminates current consumption when
the LCD is not used. When VLCDEXT = 1, R33 serves as a V
LCD
input.
The bias generator supports 1/2 biasing when LCD2B = 1 and 1/3 biasing when LCD2B = 0. In static
mode, the internal divider is disabled.
Table 36-2. Bias Voltages and external Pins
Mode
Bias
Configuration
LCD2B
Voltage Level
Pin
Condition
Static
Static
X
V1 ("1")
R33
if LCDREXT = 1 or LCDEXTBIAS = 1
V5 ("0")
R03
if R03EXT = 1
2-mux, 3-mux, 4-mux
1/2
1
V1 ("1")
R33
if LCDREXT = 1 or LCDEXTBIAS = 1
V3 ("1/2")
R13
if LCDREXT = 1 or LCDEXTBIAS = 1
V5 ("0")
R03
if R03EXT = 1
2-mux, 3-mux, 4-mux
1/3
0
V1 ("1")
R33
if LCDREXT = 1 or LCDEXTBIAS = 1
V2 ("2/3")
R23
if LCDREXT = 1 or LCDEXTBIAS = 1
V4 ("1/3")
R13
if LCDREXT = 1 or LCDEXTBIAS = 1
V5 ("0")
R03
if R03EXT = 1
5-mux to 8-mux
1/3
0
V1 ("1")
R33
if LCDREXT = 1 or LCDEXTBIAS = 1
V2 ("2/3")
R23
if LCDREXT = 1 or LCDEXTBIAS = 1
V4 ("1/3")
R13
if LCDREXT = 1 or LCDEXTBIAS = 1
V5 ("0")
R03
if R03EXT = 1