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2014-07-02 - Tiny Gecko Family - d0034_Rev1.20
507
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29.3.5 V
LCD
Selection
By default, the LCD driver runs on main external power (V
LCD
= V
DD
), see Table 29.7 (p. 507) .
An internal boost circuit can be enabled by setting VBOOSTEN in CMU_LCDCTRL and selecting the
boosted voltage by setting VLCDSEL in LCD_DISPCTRL. This will boosts V
LCD
to V
BOOST
. V
BOOST
can
be selected in the range of 3.0 V – 3.6 V by configuring VBLEV in LCD_DISPCTRL. Note that the boost
circuit is not designed to operate with the selected boost voltage, V
BOOST
, smaller than V
DD
. The boost
circuit can boost the V
LCD
up to 3.6 V when V
DD
is as low as 2.0 V.
When using the voltage booster, the LCD_BEXT pin must be connected through a 1 µF capacitor to
VSS, and the LCD_BCAP_P and LCD_BCAP_N pins must be connected to each other through a 22
nF capacitor.
It is also possible to connect a dedicated power supply to the LCD module. The LCD external power
supply must be connected to the LCD_BEXT pin and VLCDSEL in LCD_DISPCTRL must be set. In this
mode, the voltage booster should be disabled.
Table 29.7. LCD V
LCD
VLCDSEL
Mode
V
LCD
0
VDD
V
DD
(same as main external power)
1
VBOOST
Voltage booster/External V
DD
29.3.6 VBOOST Control
The boost voltage is configurable. By programming the VBLEV bits in LCD_DISPCTRL, the boost voltage
level can be adjusted between 3.0V and 3.6V.
The boost circuit will use an update frequency given by the VBFDIV bits in CMU_LCDCTRL, see
Table 29.8 (p. 507) ). It is possible to adjust the frequency to optimize performance for all kinds of LCD
panels (large capacitors may require less frequent updates, while small capacitors may require more
frequent updates). A lower update frequency would in general lead to smaller current consumption.
Table 29.8. LCD V
BOOST
Frequency
VBFDIV
V
BOOST
Update Frequency
000
LFACLK
001
LFACLK/2
010
LFACLK/4
011
LFACLK/8
100
LFACLK/16
101
LFACLK/32
110
LFACLK/64
111
LFACLK/128
29.3.7 Frame rate
It is important to choose the correct frame rate for the LCD display. Normally, the frame rate should be
between 30 and 100 Hz. A frame rate below 30 Hz may lead to flickering, while a frame rate above 100
Hz may lead to ghostering and unnecessarily high power consumption.
29.3.7.1 Clock Selection and Prescaler
The LFACLK is prescaled to LFACLK
LCDpre
in the CMU. The available prescaler settings are:
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