ad5171 Analog Devices, Inc., ad5171 Datasheet - Page 19

• Manufacturer Part Number: ad5171
• Description: 64-position Otp Digital Potentiometer
• Manufacturer: Analog Devices, Inc.

APPLICATIONS
DAC
It is common to buffer the output of the digital potentiometer as
a DAC unless the load is much larger than R
impede conversion and deliver higher current, if needed.
GAIN CONTROL COMPENSATION
The digital potentiometers are commonly used in gain controls
(Figure 41) or sensor transimpedance amplifier signal condi-
tioning applications. To avoid gain peaking, or in worst-case
oscillation due to step response, a compensation capacitor is
needed. In general, C2 in the range of a few picofarads to a few
tenths of a picofarad is adequate for the compensation.
PROGRAMMABLE VOLTAGE SOURCE WITH
BOOSTED OUTPUT
For applications that require high current adjustment, such as a
laser diode driver or tunable laser, a boosted voltage source can
be considered (Figure 42).
In this circuit, the inverting input of the op amp forces the V
to be equal to the wiper voltage set by the digital potentiometer.
The load current is then delivered by the supply via the
N‒Ch FET N
AD5171
U1
Figure 40. Programmable Voltage Reference (DAC)
Figure 42. Programmable Booster Voltage Source
Figure 41. Typical Noninverting Gain Amplifier
V
1
. N
IN
ADR03
GND
2
1
V
5V
A
B
IN
1
AD1582
power handling must be adequate to dissipate
W
U1
47kΩ
V
R1
OUT
AD8601
3
V
+V
–V
I
U2
AD5171
A
B
B
U3 2N7002
R2 100kΩ
W
4.7pF
C2
W
U1
A1
AD8601
5V
A
SIGNAL
U2
V
WB
O
LD
C
C
. The buffer can
V
O
R
BIAS
V
OUT
I
L
OUT
Rev. B | Page 19 of 24
(V
100 mA with a 5 V supply. For precision applications, a voltage
reference such as the ADR421, ADR03, or ADR370 can be
applied at Terminal A of the digital potentiometer.
LEVEL SHIFTING FOR DIFFERENT VOLTAGE
OPERATION
If the SCL and SDA signals come from a low voltage logic
controller and are below the minimum V
level shift the signals for read/write communications between
the AD5171 and the controller. Figure 43 shows one of the
implementations. For example, when the SDA1 is at 2.5 V, M1
turns off, and the SDA2 becomes 5 V. When the SDA1 is at 0 V,
M1 turns on, and the SDA2 approaches to 0 V. As a result,
proper level shifting is established. M1 and M2 should be low
threshold N-Ch power MOSFETs, such as FDV301N.
SDA1
SCL1
RESISTANCE SCALING
The AD5171 offers 5 kΩ, 10 kΩ, 50 kΩ, and 100 kΩ nominal
resistances. For users who need to optimize the resolution with
an arbitrary full range resistance, the following techniques can
be used. By paralleling a discrete resistor (Figure 44), a propor-
tionately lower voltage appears at Terminal A to Terminal B,
which is applicable only to the voltage divider mode.
This translates into a finer degree of precision because the step
size at Terminal W is smaller. The voltage can be found as
V
I
DD1
− V
V
CONTROLLER
= 2.5V
W
O
) × I
(
Figure 43. Level Shifting for Different Voltage Operation
2.5V
D
)
=
L
Figure 44. Lowering the Nominal Resistance
Rp
power. This circuit can source a maximum of
R
(
3
R
+
AB
R
AB
||
Rp
R
||
S
) 2
R2
R
M1
2
G
×
V
R1
DD
R3
64
D
A
B
D
S
×
M2
V
G
W
DD
D
Rp
IH
level (0.7 V × V
AD5171
Rp
2.7V–5.5V
AD5171
V
DD2
= 5V
DD
SDA2
SCL2
),
(5)