ad5259 Analog Devices, Inc., ad5259 Datasheet - Page 20

• Manufacturer Part Number: ad5259
• Description: Nonvolatile, I2c-compatible 256-position, Digital Potentiometer
• Manufacturer: Analog Devices, Inc.

AD5259
DISPLAY APPLICATIONS
CIRCUITRY
A special feature of the AD5259 is its unique separation of the
V
flexibility in applications that do not always provide needed
supply voltages.
In particular, LCD panels often require a V
range of 3 V to 5 V. The circuit in Figure 46 is the rare excep-
tion in which a 5 V supply is available to power the digital
potentiometer.
1μF
In the more common case shown in Figure 47, only analog 14.4 V
and digital logic 3.3 V supplies are available. By placing discrete
resistors above and below the digital potentiometer, V
now be tapped off the resistor string itself. Based on the chosen
resistor values, the voltage at V
allowing the wiper to be safely operated all the way up to 4.8 V.
The current draw of V
it is only on the order of microamps. V
3.3 V digital supply because V
is needed when writing to the EEPROM. It would be imprac-
tical to try and source 35 mA through the 70 kΩ resistor,
therefore, V
C1
LOGIC
VCC (~3.3V)
MCU
and V
10kΩ
R6
LOGIC
DD
10kΩ
R5
supply pins. The separation provides greater
Figure 46. V
is not connected to the same node as V
5V
AD5259
DD
V
V
SCL
SDA
GND
DD
LOGIC
will not affect that node’s bias because
COM
14.4V
A
B
Adjustment Application
LOGIC
R1
70kΩ
R2
10kΩ
R3
25kΩ
DD
W
in this case equals 4.8 V,
will draw the 35 mA which
LOGIC
–
+
AD8565
U1
COM
is tied to the MCU’s
voltage in the
3.5V < V
DD
COM
DD
can
.
< 4.5V
Rev. A | Page 20 of 24
For this reason, V
supply pins that can either be tied together or treated inde-
pendently; V
and V
flexibility.
1μF
For a more detailed look at this application, refer to the article,
“Simple VCOM Adjustment uses any Logic Supply Voltage” in
the September 30, 2004 issue of EDN magazine.
C1
VCC (~3.3V)
Figure 47. Circuitry When a Separate Supply is Not Available for V
MCU
DD
10kΩ
biasing up the A, B, and W terminals for added
R6
SUPPLIES POWER
TO BOTH THE
MICRO AND THE
LOGIC SUPPLY OF
THE DIGITAL POT
LOGIC
10kΩ
R5
LOGIC
supplying the logic/EEPROM with power,
AD5259
and V
V
V
SCL
SDA
GND
DD
LOGIC
14.4V
DD
A
B
R1
70kΩ
R2
10kΩ
R3
25kΩ
are provided as two separate
W
–
+
AD8565
U1
3.5V < V
COM
DD
< 4.5V