ad5258 Analog Devices, Inc., ad5258 Datasheet - Page 20

• Manufacturer Part Number: ad5258
• Description: Nonvolatile, I2c-compatible 64-position, Digital Potentiometer
• Manufacturer: Analog Devices, Inc.

AD5258
DISPLAY APPLICATIONS
CIRCUITRY
A special feature of the AD5258 is its unique separation of
the V
to provide greater flexibility in applications that do not always
provide the needed supply voltages.
In particular, LCD panels often require a V
the range of 3 V to 5 V. The circuit in Figure 44 is the rare
exception in which a 5 V supply is available to power the
digital potentiometer.
1µF
More commonly, only analog 14.4 V and digital logic 3.3 V sup-
plies are available (see Figure 45). By placing discrete resistors
above and below the digital potentiometer, V
off the resistor string itself. Based on the chosen resistor values,
the voltage at V
be safely operated up to 4.8 V. The current draw of V
C1
VCC (~3.3V)
MCU
LOGIC
10kΩ
R6
and V
10kΩ
R5
DD
Figure 44. V
DD
in this case equals 4.8 V, allowing the wiper to
supply pins. The reason for doing this is
5V
AD5258
V
V
SCL
SDA
GND
DD
LOGIC
COM
14.4V
Adjustment Application
A
B
R1
70kΩ
R2
10kΩ
R3
25kΩ
W
–
+
AD8565
COM
U1
DD
voltage in
can be tapped
3.5V < V
DD
will not
COM
< 4.5V
Rev. A | Page 20 of 24
affect that node’s bias because it is only on the order of
microamps. V
digital supply because V
when writing to the EEPROM. It would be impractical to try to
source 35 mA through the 70 kΩ resistor; therefore, V
not connected to the same node as V
For this reason, V
supply pins that can either be tied together or treated inde-
pendently; V
V
1µF
For a more detailed look at this application, refer to the article,
“Simple V
September 30, 2004, issue of EDN magazine.
C1
DD
VCC (~3.3V)
Figure 45. Circuitry When a Separate Supply Is Not Available for V
biases up the A, B, and W terminals for added flexibility.
MCU
10kΩ
R6
COM
SUPPLIES POWER
TO BOTH THE MCU
AND THE LOGIC
SUPPLY OF THE
DIGITAL
POTENTIOMETER
LOGIC
10kΩ
Adjustment uses any Logic-Supply Voltage” in the
LOGIC
R5
LOGIC
supplies the logic/EEPROM with power, and
is tied to the microcontroller’s (MCU) 3.3 V
AD5258
and V
V
V
SCL
SDA
GND
LOGIC
DD
LOGIC
14.4V
DD
A
B
will draw the 35 mA that is needed
R1
70kΩ
R2
10kΩ
R3
25kΩ
are provided as two separate
W
DD
.
–
+
AD8565
U1
3.5V < V
LOGIC
COM
DD
is
< 4.5V