ad5160 Analog Devices, Inc., ad5160 Datasheet - Page 13

• Manufacturer Part Number: ad5160
• Description: 256-position Spi Compatible Digital Potentiometer
• Manufacturer: Analog Devices, Inc.

PROGRAMMING THE POTENTIOMETER DIVIDER
Voltage Output Operation
The digital potentiometer easily generates a voltage divider at
wiper-to-B and wiper-to-A proportional to the input voltage at
A-to-B. Unlike the polarity of V
positive, voltage across A-B, W-A, and W-B can be at either
polarity.
If ignoring the effect of the wiper resistance for approximation,
connecting the A terminal to 5 V and the B terminal to ground
produces an output voltage at the wiper-to-B starting at 0 V up
to 1 LSB less than 5 V. Each LSB of voltage is equal to the
voltage applied across terminal AB divided by the 256 positions
of the potentiometer divider. The general equation defining the
output voltage at V
voltage applied to terminals A and B is
For a more accurate calculation, which includes the effect of
wiper resistance, V
Operation of the digital potentiometer in the divider mode
results in a more accurate operation over temperature. Unlike
the rheostat mode, the output voltage is dependent mainly on
the ratio of the internal resistors R
absolute values. Therefore, the temperature drift reduces to
15 ppm/°C.
SPI COMPATIBLE 3-WIRE SERIAL BUS
The AD5160 contains a 3-wire SPI compatible digital interface
(SDI, CS , and CLK). The 8-bit serial word must be loaded MSB
first. The format of the word is shown in Table 5.
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 debounced by a
flip-flop or other suitable means. When CS is low, the clock
loads data into the serial register on each positive clock edge
(see Figure 36).
The data setup and data hold times in the specification table
determine the valid timing requirements. The AD5160 uses an
8-bit serial input data register word that is transferred to the
internal RDAC register when the CS line returns to logic high.
Extra MSB bits are ignored.
V
V
W
W
(
(
D
D
)
)
=
=
256
R
D
WB
256
V
W
W
(
, can be found as
D
A
with respect to ground for any valid input
)
+
V
256
A
256
+
−
R
D
WA
DD
256
V
WA
to GND, which must be
B
(
D
and R
)
V
B
WB
and not the
(3)
(4)
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ESD PROTECTION
All digital inputs are protected with a series input resistor and
parallel Zener ESD structures shown in Figure 39 and Figure 40.
This applies to the digital input pins SDI, CLK, and CS .
TERMINAL VOLTAGE OPERATING RANGE
The AD5160 V
conditions for proper 3-terminal digital potentiometer
operation. Supply signals present on terminals A, B, and W that
exceed V
biased diodes (see Figure 41).
POWER-UP SEQUENCE
Since the ESD protection diodes limit the voltage compliance at
terminals A, B, and W (see Figure 41), it is important to power
V
otherwise, the diode will be forward biased such that V
powered unintentionally and may affect the rest of the user’s
circuit. The ideal power-up sequence is in the following order:
GND, V
powering V
long as they are powered after V
DD
/GND before applying any voltage to terminals A, B, and W;
DD
Figure 41. Maximum Terminal Voltages Set by V
DD
, digital inputs, and then V
or GND will be clamped by the internal forward
A
Figure 40. ESD Protection of Resistor Terminals
, V
DD
B
Figure 39. ESD Protection of Digital Pins
, V
and GND power supply defines the boundary
W
, and the digital inputs is not important as
A,B,W
340Ω
V
SS
V
SS
DD
/GND.
LOGIC
A/B/W
. The relative order of
DD
V
V
and V
W
A
B
DD
SS
AD5160
SS
DD
will be