AD5227 데이터 시트보기 (PDF) - Analog Devices
부품명
상세내역
일치하는 목록
AD5227 Datasheet PDF : 16 Pages
| |||
AD5227
THEORY OF OPERATION
The AD5227 is a 64-position 3-terminal digitally controlled
potentiometer device. It presets to a midscale at system power-
on. When CS is enabled, changing the resistance settings is
achieved by clocking the CLK pin. It is negative-edge triggered,
and the direction of stepping is determined by the state of the
U/D input. When the wiper reaches the maximum or the
minimum setting, additional CLK pulses do not change the
wiper setting.
VDD
AD5227
CS
A
6-BIT UP/DOWN
U/D
CONTROL
LOGIC
W
CLK
B
GND
POR
MIDSCALE
WIPER
REGISTER
Figure 24. Functional Block Diagram
A
RS
D0
D1
RS
D2
D3
RS
D4
D5
W
RDAC
RW
UP/DOWN
CTRL AND
DECODE
RS
B
RS = RAB/64
Figure 25. AD5227 Equivalent RDAC Circuit
PROGRAMMING THE DIGITAL POTENTIOMETERS
Rheostat Operation
If only the W-to-B or W-to-A terminals are used as variable
resistors, the unused terminal can be opened or shorted with W.
This operation is called rheostat mode and is shown in Figure 26.
A
A
A
W
W
W
B
B
B
Figure 26. Rheostat Mode Configuration
The end-to-end resistance, RAB, has 64 contact points accessed
by the wiper terminal, plus the B terminal contact, assuming
that RWB is used (see Figure 25). Clocking the CLK input steps,
RWB by one step. The direction is determined by the state of
U/D pin. The change of RWB can be determined by the number
of clock pulses, provided that the AD5227 has not reached its
maximum or minimum scale. ΔRWB can, therefore, be
approximated as
ΔRWB
=
±⎜⎛CP ×
⎝
RAB
64
+
RW
⎟⎞
⎠
(1)
where:
CP is the number of clock pulses.
RAB is the end-to-end resistance.
RW is the wiper resistance contributed by the on-resistance of
the internal switch.
Since in the lowest end of the resistor string a finite wiper
resistance is present, care should be taken to limit the current
flow between W and B in this state to a maximum pulse current
of no more than 20 mA. Otherwise, degradation or possible
destruction of the internal switches can occur.
Similar to the mechanical potentiometer, the resistance of the
RDAC between the Wiper W and Terminal A also produces a
digitally controlled complementary resistance, RWA. When these
terminals are used, the B terminal can be opened or shorted to
W. Similarly, ΔRWA can be approximated as
ΔRWA
=
±⎜⎝⎛ (64
− CP ) RAB
64
+
RW
⎟⎠⎞
(2)
Equations 1 and 2 do not apply when CP = 0.
The typical distribution of the resistance tolerance from device
to device is process lot dependent. It is possible to have ±20%
tolerance.
Potentiometer Mode Operation
If all three terminals are used, the operation is called
potentiometer mode. The most common configuration is the
voltage divider operation as shown in Figure 27.
VI
A
VC
W
B
Figure 27. Potentiometer Mode Configuration
Rev. B | Page 10 of 16
Share Link: 