isl24212 Intersil Corporation, isl24212 Datasheet - Page 6

• Manufacturer Part Number: isl24212
• Description: Programmable Vcom Calibrator With Eeprom And Output Buffer
• Manufacturer: Intersil Corporation

Application Information
LCD panels have a V
set to minimize flicker. Figure 3 shows a typical V
circuit using a mechanical potentiometer, and the equivalent
circuit replacement using the ISL24212. Having a digital counter
interface enables automatic, digital flicker minimization during
production test and alignment. After programming, the counter
interface is no longer needed - the ISL24212 automatically powers
up with the correct V
The ISL24212 uses a digitally controllable potentiometer (DCP),
with 256 steps of resolution (see Figure 4) to change the current
drawn at the DVR_OUT pin, which then changes the voltage
created by the R
voltage is then buffered by A2 to generate a buffered output voltage
at the V
an LCD panel. The amount of current sunk is controlled by the
setting of the DCP, which is recalled at power-up from the
ISL24212’s internal EEPROM. The EEPROM is typically
programmed during panel manufacture. As noted in the
“Electrical Specifications” on page 4, the ISL24212 requires a
minimum AV
will work in normal operation down to 4.5V after the EEPROM
has been programmed, with no additional EEPROM writing.
DCP (Digitally Controllable Potentiometer)
The DCP controls the voltage that ultimately controls the SET
current. Figure 4 shows the relationship between the register
value and the DCP’s tap position. Note that a register value of 0
selects the first step of the resistor string. The output voltage of
the DCP is given in Equation 1:
V
DCP
=
COM_OUT
FIGURE 3. MECHANICAL ADJUSTMENT REPLACEMENT
⎛
⎝
R
R
R
RegisterValue
-------------------------------------------------- -
1
2
SET
= R
= R
= R
DD
A
B
+R
A
1
R
R
256
voltage of 10.8V for EEPROM programming, but
R
pin, capable of directly driving the V
AV
1
2
- R
C
B
20R
+ R
DD
COM
2
COM
B
I
resistor divider (see Figure 5). The DVR_OUT
A
OUT
R
C
+
(common voltage) that must be precisely
voltage programmed previously.
1
R
R
R
DVR_OUT
ISL24212
⎞
⎠
A
B
C
AV
⎛
⎝
V
AV
--------------
DD
DD
SET
20
6
DD
R
⎞
⎠
SET
VCOM_OUT
AV
IN
DD
N
COM
COM
V
V
COM
COM
adjustment
input of
ISL24212
(EQ. 1)
Output Current Sink
Figure 5 shows the schematic of the DVR_OUT current sink. The
combination of amplifier A1, transistor Q1, and resistor R
forms a voltage-controlled current source, with the voltage
determined by the DCP setting.
The external R
that can be pulled from the DVR_OUT node. The relationship
between I
I
DVROUT
AV
DD
=
DVR_OUT
GND
V
-------------
R
FIGURE 4. SIMPLIFIED SCHEMATIC OF DCP
DCP
SET
SET
V
AV
20
FIGURE 5. CURRENT SINK CIRCUIT
DCP
=
resistor sets the full-scale (maximum) sink current
DD
and Register Value is shown in Equation 2.
A1
R
⎛
⎝
19R
RegisterValue
-------------------------------------------------- -
AV
DD
256
SET
I
Q1
DVR_ OUT
OUT
255
254
253
252
251
2
1
0
REGISTER
+
V
SAT
VALUE
V
1
R
SET
⎞
⎠
SET
⎛
⎝
A2
AV
--------------
= V
I
20
V
DVR_OUT
DD
DCP
DCP
⎞
⎠
⎛
⎝
= I
------------ -
R
SET
AV
IN
1
VCOM_OUT
OUT
N
DD
⎞
⎠
March 15, 2011
* R
R
R
1
2
SET
FN7590.0
SET
V
OUT
(EQ. 2)