AD5259 查看數據表（PDF） - Analog Devices
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AD5259 Datasheet PDF : 24 Pages
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AD5259
DISPLAY APPLICATIONS
CIRCUITRY
A special feature of the AD5259 is its unique separation of the
VLOGIC and VDD supply pins. The separation provides greater
flexibility in applications that do not always provide needed
supply voltages.
In particular, LCD panels often require a VCOM voltage in the
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.
VCC (~3.3V)
5V
14.4V
C1
1μF
R6 R5
10kΩ 10kΩ
MCU
R1
70kΩ
AD5259
VDD
VLOGIC
A
SCL
SDA B
R2
10kΩ
W
GND
R3
25kΩ
–
U1
AD8565
+
3.5V < VCOM < 4.5V
Figure 46. VCOM Adjustment Application
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, VDD can
now be tapped off the resistor string itself. Based on the chosen
resistor values, the voltage at VDD in this case equals 4.8 V,
allowing the wiper to be safely operated all the way up to 4.8 V.
The current draw of VDD will not affect that node’s bias because
it is only on the order of microamps. VLOGIC is tied to the MCU’s
3.3 V digital supply because VLOGIC will draw the 35 mA which
is needed when writing to the EEPROM. It would be imprac-
tical to try and source 35 mA through the 70 kΩ resistor,
therefore, VLOGIC is not connected to the same node as VDD.
For this reason, VLOGIC and VDD are provided as two separate
supply pins that can either be tied together or treated inde-
pendently; VLOGIC supplying the logic/EEPROM with power,
and VDD biasing up the A, B, and W terminals for added
flexibility.
VCC (~3.3V) SUPPLIES POWER
TO BOTH THE
MICRO AND THE
LOGIC SUPPLY OF
THE DIGITAL POT
14.4V
R1
70kΩ
C1
1μF
AD5259
R6 R5
10kΩ 10kΩ
VDD
MCU
VLOGIC
A
SCL
SDA B
R2
10kΩ
W
GND
R3
25kΩ
–
U1
AD8565
+
3.5V < VCOM < 4.5V
Figure 47. Circuitry When a Separate Supply is Not Available for VDD
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.
Rev. A | Page 20 of 24
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