AD5203 Analog Devices, AD5203 Datasheet - Page 10

• Manufacturer Part Number: AD5203
• Description: 8-Bit Dual Nonvolatile Memory Digital Potentiometer
• Manufacturer: Analog Devices

AD5203
PROGRAMMING THE POTENTIOMETER DIVIDER
Voltage Output Operation
The digital potentiometer easily generates an output voltage
proportional to the input voltage applied to a given terminal.
For example connecting A–terminal to +5 V and B–terminal to
ground produces an output voltage at the wiper which can be
any value starting at zero volts up to 1 LSB less than +5 V.
Each LSB of voltage is equal to the voltage applied across ter-
minal AB divided by the 64 position resolution of the potenti-
ometer divider. The general equation defining the output
voltage with respect to ground for any given input voltage ap-
plied to terminals AB is:
Operation of the digital potentiometer in the divider mode
results in more accurate operation over temperature. Here the
output voltage is dependent on the ratio of the internal resistors
not the absolute value, therefore the drift improves to 20 ppm/ C.
DIGITAL INTERFACING
The AD5203 contains a standard three-wire serial input control
interface. The three inputs are clock (CLK), CS and serial data
input (SDI). The positive-edge sensitive CLK input requires
clean transitions to avoid clocking incorrect data into the serial
input register. Standard logic families work well. If mechanical
switches are used for product evaluation they should be de-
bounced by a flip-flop or other suitable means. The Figure 35
block diagram shows more detail of the internal digital cir-
cuitry. When CS is taken active low the clock loads data into
the serial register on each positive clock edge, see Table III.
SHDN
SDO
CLK
SDI
CS
DO
DI
SER
REG
DGND
V
Figure 35. Block Diagram
A1
A0
D5
D0
W
(Dx) = Dx/64
ADDR
DEC
6
EN
RS
D5
D5
D0
D0
AD5203
DAC
DAC
V
LAT
LAT
#1
#4
R
R
R
R
AB
AGND
+ V
B
W1
A1
B1
V
A4
W4
B4
DD
–10–
The serial-data-output (SDO) pin contains an open drain
n-channel FET. This output requires a pull-up resistor in order
to transfer data to the next package’s SDI pin. The pull-up
resistor termination voltage may be larger than the V
of the AD5203 SDO output device, e.g., the AD5203 could
operate at V
device could be set at +5 V. This allows for daisy chaining sev-
eral RDACs from a single processor serial data line. Clock pe-
riod needs to be increased when using a pull-up resistor to the
SDI pin of the following device in the series. Capacitive loading
at the daisy chain node SDO-SDI between devices must be
accounted for to successfully transfer data. When daisy chaining
is used, the CS should be kept low until all the bits of every
package are clocked into their respective serial registers insuring
that the address bits and data bits are in the proper decoding
location. This would require 16 bits of address and data comply-
ing to the word format provided in Table I if two AD5203 four-
channel RDACs are daisy chained. During shutdown, SHDN
the SDO output pin is forced to the off (logic high state) to
disable power dissipation in the pull-up resistor. See Figure 37
for equivalent SDO output circuit schematic.
CLK CS
L
P
X
X
X
X
X
NOTE: P = positive edge, X = don’t care, SR = shift register.
L
L
P
H
X
H
H
Table II. Input Logic Control Truth Table
DD
A1
0
0
1
1
RS
H
H
H
H
L
P
H
= 3.3 V and the pull-up for interface to the next
Table III. Address Decode Table
SHDN Register Activity
H
H
H
H
H
H
L
A0
0
1
0
1
No SR effect, enables SDO pin.
Shift one bit in from the SDI pin.
The eighth previously entered bit
is shifted out of the SDO pin.
Load SR data into RDAC latch
based on A1, A0 decode (Table III).
No Operation.
Sets all RDAC latches to midscale,
wiper centered and SDO latch
cleared.
Latches all RDAC latches to 20
Open circuits all Resistor A–termi-
nals, connects W to B, turns off
SDO output transistor.
Latch Decoded
RDAC#1
RDAC#2
RDAC#3
RDAC#4
DD
supply
REV. 0
H
.