PRELIMINARY TECHNICAL DATA
Charge Pump Regulator & COM Driver
for Color TFT Panel
a
ADM8840
Preliminary Technical Data
Programmable COM Driver to prevent Screen-Burn
3 Voltages (5.0V,15.0V,-15.0V) from one 3V Supply
Power Efficiency optimised for use with TFT in mobile
phones
FEATURES
FUNCTIONAL BLOCK DIAGRAM
-15V
C9
0.22F
VOLTAGE
INVERTER
C4+
C4-
C4
Low Quiescent Current
Low Shutdown Current (<5uA)
ShutdownFunction
0.22F
+15V
C8
ADM8840
0.22F
C2+
C2
TRIPLE
0.22
F
C2-
C3+
VOLTAGE
TRIPLER
C3
DOUBLE
0.22
F
APPLICATIONS
Handheld Instruments
TFT LCD Panels
C3-
OSCILLATOR
TIMING
GENERATOR
5VIN
+5V
5VOUT
C7
2.2F
LDO
VOLTAGE
REGULATOR
SHUTDOWN
CONTROL
SHDN
DISCHARGE
CellularPhones
VOUT
C10
C1+
C1-
C1
VOLTAGE
DOUBLER
3.3F
CONTROL
LOGIC
3.3F
C6
4.7
F
V
CC
C5+
C5
VOLTAGE
ADDER
3.3F
C5-
DAC1_IN
DAC1_SD
VREF
ADD_OUT
C11
GENERAL DESCRIPTION
8
8
4.7F
INT/EXT
DAC
DAC
DAC
1
2
+
-
CLK
The ADM8840 combines a charge pump regulator and a
Common Line (COM) driver in a single chip solution for use
in TFT LCD’s. The device provides an LCD controller and
grayscale DAC supply voltage of 5.0V (±±2)ꢀ ± gate drive
voltages of +15V and -15V and a COM driver voltage. This
COM Driver voltage alternates the polarity of the Common
line voltage every line (or every frame) on the display in order
to prevent screen-burn occuring over time. The ADM8840
is powered by a single 3.0V supply.
1
SERIAL
INTERFACE
DATA
CS / LDAC
TRANS_OUT
C12
INT/EXT
DAC
2
4.7F
POWER
BUFFER
LEVEL
TRANSLATOR
COM_OUT_AC
C13
COM_IN
4.7F
+
COM_OUT
DAC2_SD
DAC2_IN
5.5k⍀
-
C
PANEL
22nF
GND
The ADM8840 has an internal 100KHz oscillator for driving
the charge pumps.
The COM Driver section of the ADM8840 can be used to
generate the alternate frame or line inversion of the COM
line of the LCD panel. The ADM8840 receives the COM
clock from the controller with a frequency up to 10kHz and
allows programmable conditioning of its amplitude and
centre voltage through the use of on-board DAC’s. This
allows programmable elimination of display flicker caused
by the COM inversion.
The ADM8840 provides power up sequencing of the -15V
and +15V gate drive outputsꢀ ensuring the -15V starts to
power up before the +15V.
The ADM8840 has a number of power save featuresꢀ includ-
ing low power Shutdown. The 5.0V output consumes the
most powerꢀ so Power Efficiency is also maximised on this
output with an oscillator enabling scheme (Green IdleTM).
The COM_OUT amplitude can be programmed from 4.0V
to 7.0V in steps of ±8mV. The COM_OUT centre voltage
can be programmed to 0.9V to ±.8V in steps of 14mV.
The ADM8840 is fabricated using CMOS technology for
minimal power consumption. The part is packaged in a 3±-
pin LFCSP package.
TM Green Idle is a registered trademark of Analog Devices Inc.
REV. PrG 2/03
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700
WorldWide Web Site: http://www.analog.com
Fax: 781/326-8703
Analog Devices, Inc., 2003