EVAL-AD5262EBZ Analog Devices Inc, EVAL-AD5262EBZ Datasheet - Page 16

• Manufacturer Part Number: EVAL-AD5262EBZ
• Description: EVALUATION BOARD
• Manufacturer: Analog Devices Inc

Specifications of EVAL-AD5262EBZ

• Main Purpose: Digital Potentiometer
• Utilized Ic / Part: AD5262
• Primary Attributes: Dual Channel, 256 Positions
• Secondary Attributes: SPI Interface
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Embedded: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

AD5260/AD5262
The target RDAC latch is loaded with the last eight bits of
the serial data word completing one RDAC update. For the
AD5262, two separate 9-bit data words must be clocked in to
change both VR settings.
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
schematic.
All digital inputs are protected with a series input resistor and
parallel Zener ESD structure as shown in Figure 50. This applies
to the CS , SDI, SDO, PR , SHDN , and CLK digital input pins.
DAISY-CHAIN OPERATION
The serial data output (SDO) pin contains an open-drain N-
channel FET. This output requires a pull-up resistor to transfer
data to the SDI pin of the next package. This allows for daisy-
chaining several RDACs from a single processor serial data line.
The pull-up resistor termination voltage can be larger than the
V
period when using a pull-up resistor to the SDI pin of the
following device in series because capacitive loading at the
daisy-chain node connecting SDO and SDI between devices
may induce time delay to subsequent devices. Users should
be aware of this potential problem to achieve data transfer
successfully (see Figure 52). If two AD5260s are daisy-chained,
this requires a total of 16 bits of data. The first eight bits, complying
with the format shown in Table 2, go to U2, and the second
eight bits with the same format go to U1. The CS pin should be
kept low until all 16 bits are clocked into their respective serial
DD
supply voltage. It is recommended to increase the clock
Figure 49. Detail SDO Output Schematic of the AD5260
SHDN
CLK
CLK
SDI
SDI
CS
CS
PR
Figure 49
Figure 51. ESD Protection of Resistor Terminals
AD5260/AD5262
Figure 48. Equivalent Input Control Logic
Figure 50. ESD Protection of Digital Pins
REGISTER
SERIAL
A, B, W
for the equivalent SDO output circuit
340Ω
D
CK
V
SS
RS
REGISTER
Q
DECODE
SERIAL
ADDR
LOGIC
RDAC1
RDAC2
SDO
Rev. A | Page 16 of 24
registers, and the CS pin is then pulled high to complete the
operation.
RDAC STRUCTURE
The RDAC contains a string of equal resistor segments with an
array of analog switches that act as the wiper connection. The
number of positions is the resolution of the device. The AD5260/
AD5262 have 256 connection points, allowing it to provide better
than 0.4% settability resolution. Figure 53 shows an equivalent
structure of the connections between the three terminals that
make up one channel of the RDAC. SW
on, while one of the switches SW(0) to SW(2
time, depending on the resistance position decoded from the
data bits. Because the switch is not ideal, there is a 60 Ω wiper
resistance, R
and temperature. The lower the supply voltage is, the higher the
wiper resistance becomes. Similarly, the higher the temperature
is, the higher the wiper resistance becomes. Users should be
aware of the contribution of the wiper resistance when accurate
prediction of the output resistance is needed.
PROGRAMMING THE VARIABLE RESISTOR
Rheostat Operation
The nominal resistances of the RDAC between Terminal A and
Terminal B are available with values of 20 kΩ, 50 kΩ, and 200 kΩ.
The final three digits of the part number determine the nominal
resistance value, for example, 20 kΩ = 20, 50 kΩ = 50, 200 kΩ =
200. The nominal resistance (R
CONTROLLER
SCLK
MICRO-
SHDN
W
DIGITAL CIRCUITRY
OMITTED FOR CLARITY
. Wiper resistance is a function of supply voltage
MOSI
D1
D0
D7
D6
D5
D4
D3
D2
SS
Figure 53. Simplified RDAC Architecture
Figure 52. Daisy-Chain Configuration
DECODE
LATCH
RDAC
AND
AD5260
SDI
CS CLK
U1
SDO
R
R
R
R
S
S
S
S
AB
) of the VR has 256 contact points
V
DD
R
R
2.2kΩ
S
P
= R
AB
A
AD5260
SDI
and SW
/2
CS CLK
N
U2
N
SDO
– 1) is on one at a
Ax
Wx
Bx
B
are always