Datasheet

AD5200/AD5201
–11–
CODE – Decimal
100.0
10.0
0.1
032
THEORETICAL I
MAX
– mA
1.0
64 96 128
160
192 224 256
R
AB
= 10k
R
AB
= 50k
TPC 31. AD5200 I
MAX
vs. Code
CODE – Decimal
100.0
10.0
0.1
04
THEORETICAL I
MAX
– mA
1.0
812
16
20 24
28
32
R
AB
= 10k
R
AB
= 50k
TPC 32. AD5201 I
MAX
vs. Code
OPERATION
The AD5200/AD5201 provide 255 and 33 positions digitally-
controlled variable resistor (VR) devices. Changing the
programmed VR settings is accomplished by clocking in an 8-bit
serial data word for AD5200, and a 6-bit serial data word for
AD5201, into the SDI (Serial Data Input) pins. Table I provides
the serial register data word format. The AD5200/AD5201 are
preset to a midscale internally during power-on condition. In
addition, the AD5200/AD5201 contain power shutdown
SHDN pins that place the RDAC in a zero power consump-
tion state where the immediate switches next to Terminals A and
B are open-circuited. Meanwhile, the wiper W is connected to B
terminal, resulting in only leakage current consumption in the VR
structure. During shutdown, the VR latch contents are maintained
when the RDAC is inactive. When the part is returned from
shutdown, the stored VR setting will be applied to the RDAC.
Table I. AD5200 Serial-Data Word Format
7B6B5B4B3B2B1B0B
7D6D5D4D3D2D1D0D
BSMBSL
2
7
2
0
Table II. AD5201 Serial-Data Word Format
5B * 4B3B2B1B0B
5D * 4D3D2D1D0D
BSMBSL
2
5
2
0
*Six data bits are needed for 33 positions.
PROGRAMMING THE VARIABLE RESISTOR
Rheostat Operation
The nominal resistance of the RDAC between Terminals A and
B are available with values of 10 kΩ and 50 kΩ. The final two
digits of the part number determine the nominal resistance
value, e.g., 10 kΩ = 10 and 50 kΩ = 50. The nominal resistance
(R
AB
) of AD5200 has 256 contact points accessed by the wiper
terminal. The 8-bit data word in the RDAC latch of AD5200 is
decoded to select one of the 256 possible settings. In both parts,
the wiper’s first connection starts at the B terminal for data 00
H
.
This B-terminal connection has a wiper contact resistance of
50 Ω as long as valid V
DD
/V
SS
is applied, regardless of the nominal
resistance. For a 10 kΩ part, the second connection of AD5200 is
the first tap point with 89 Ω [R
WB
= R
AB
/255 + R
W
= 39 Ω + 50 Ω]
for data 01
H
. The third connection is the next tap point representing
78 + 50 = 128 Ω for data 02
H
. Due to its unique internal structure,
AD5201 has 5-bit + 1 resolution, but needs a 6-bit data word to
achieve the full 33 steps resolution. The 6-bit data word in the
RDAC latch is decoded to select one of the 33 possible settings.
Data 34 to 63 will automatically be equal to Position 33. The
wiper 00
H
connection of AD5201 gives 50 Ω. Similarly, for a
10 kΩ part, the first tap point of AD5201 yields 363 Ω for
data 01
H
, 675 Ω for data 02
H
. For both AD5200 and AD5201,
each LSB data value increase moves the wiper up the resistor
ladder until the last tap point is reached. Figures 2a and 2b show
the simplified diagrams of the equivalent RDAC circuits.