Datasheet

AD5231 Data Sheet
Rev. D | Page 24 of 28
V+
V–
AD8552
AD5231
V
O
V+
V–
AD8552
–2.5VREF
B
A
W
A1
U1
+2.5VREF
V
OUT
V
IN
TRIM
GND
ADR421
+5V
–5V
–5V
+5V
R R
A2
+5V
02739-048
Figure 49. 10-Bit Bipolar DAC
10-BIT UNIPOLAR DAC
Figure 50 shows a unipolar 10-bit DAC using AD5231. The
buffer is needed to drive various leads.
AD5231
V+
V–
AD8601
W
A1
GND
AD1582
5V
5V
U1
3
A
B
V
O
1
2
V
OUT
V
IN
02739-049
Figure 50. 10-Bit Unipolar DAC
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 (see Figure 51).
AD5231
V+
V–
W
AD8601
A
B
V
IN
V
OUT
I
L
2N7002
R
BIAS
SIGNAL
C
C
LD
U2
02739-058
Figure 51. Programmable Booster Voltage Source
In this circuit, the inverting input of the op amp forces the V
OUT
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
1
. N
1
power handling must be adequate to dissipate
(V
i
− V
O
) × I
L
power. This circuit can source a maximum of
100 mA with a 5 V supply.
For precision applications, a voltage reference such as ADR421,
ADR03, or ADR370 can be applied at Terminal A of the digital
potentiometer.
PROGRAMMABLE CURRENT SOURCE
A programmable current source can be implemented with the
circuit shown in Figure 52.
V+
V–
OP1177
U2
V
IN
SLEEP
REF191
GND
V
OUT
3
2
4
6
U1
AD5231
W
A
B
V
L
I
L
+5V
–5V
+5V
+
–
–2.048V TOV
L
0V TO (2.048V + V
L
)
R
S
102Ω
C1
1µF
R
L
100Ω
02739-051
Figure 52. Programmable Current Source
REF191 is a unique low supply, headroom precision reference
that can deliver the 20 mA needed at 2.048 V. The load current
is simply the voltage across Terminals B–W of the digital
potentiometer divided by R
S
:
1024×
×
=
S
REF
L
R
D
V
I
(7)
The circuit is simple, but be aware that there are two issues.
First, dual-supply op amps are ideal because the ground
potential of REF191 can swing from −2.048 V at zero scale to V
L
at full scale of the potentiometer setting. Although the circuit
works under single-supply, the programmable resolution of the
system is reduced. Second, the voltage compliance at V
L
is
limited to 2.5 V or equivalently a 125 Ω load. Should higher
voltage compliance be needed, users can consider digital
potentiometers AD5260, AD5280, and AD7376. Figure 53
shows an alternate circuit for high voltage compliance.
To achieve higher current, such as when driving a high power
LED, the user can replace the UI with an LDO, reduce R
S
, and
add a resistor in series with the digital potentiometer’s
A terminal. This limits the potentiometer’s current and
increases the current adjustment resolution.