LCD_C Operation
937
SLAU367P – October 2012 – Revised April 2020
Copyright © 2012–2020, Texas Instruments Incorporated
LCD_C Controller
With LCDBLKMODx = 11 the LCD controller switches automatically between the memories using the
divider to generate the blinking frequency. After LCDBLKMODx = 11 is selected, the memory to be
displayed for the first half a BLKCLK period is the LCD memory. In the second half, the blinking memory is
used as display memory. Switching between the memories is synchronized to the frame boundaries.
36.2.5 LCD Voltage And Bias Generation
The LCD_C module allows selectable sources for the peak output waveform voltage, V1, as well as the
fractional LCD biasing voltages V2 to V5. V
LCD
may be sourced from V
CC
, an internal charge pump, or
externally.
All internal voltage generation is disabled if the selected clock source (ACLK or VLOCLK) is turned off
(OSCOFF = 1) or the LCD_C module is disabled (LCDON = 0).
36.2.5.1 LCD Voltage Selection
V
LCD
is sourced from V
CC
when VLCDEXT = 0, VLCDx = 0, and VREFx = 0. V
LCD
is sourced from the
internal charge pump when VLCDEXT = 0, VLCDCPEN = 1, and VLCDx > 0. The charge pump is always
sourced from DV
CC
. The VLCDx bits provide a software selectable LCD voltage from 2.6 V to 3.44 V
(typical) independent of DV
CC
. See the device-specific data sheet for specifications.
When the internal charge pump is used, a 4.7-µF or larger capacitor must be connected between the
LCDCAP pin and ground. If no capacitor is connected and the charge pump is enabled, the
LCDNOCAPIFG interrupt flag is set, and the charge pump is disabled to prevent damage to the device.
To reduce system noise the charge pump can be temporarily disabled. It is disabled when LCDCPEN = 0
and re-enabled when LCDCPEN is changed back to 1. If the charge pump is temporarily disabled the
voltage stored on the external capacitor is used for the LCD voltages until the charge pump is re-enabled.
Some devices can also automatically disable the charge pump during certain periods of time (for example
during an ADC conversion). To enable this feature set the corresponding LCDCPDISx bits in the
LCDBCPCTL register. For details see the device-specific data sheet (if the feature is not listed in the data
sheet it is not supported by the respective device).
NOTE:
Capacitor Required For Internal Charge Pump
A 4.7-µF or larger capacitor must be connected from the LCDCAP pin to ground when the
internal charge pump is enabled. If no capacitor is connected, the LCDNOCAPIFG interrupt
flag is set and the charge pump is disabled.
The internal charge pump may use an external reference voltage when VLCDREFx = 01 (and LCDREXT
= 0 and LCDEXTBIAS = 0). In this case, the charge pump voltage is set to a multiply of the external
reference voltage according to the VLCDx bits setting.
When VLCDEXT = 1, V
LCD
is sourced externally from the LCDCAP, pin and the internal charge pump is
disabled.