AD5251 Analog Devices, AD5251 Datasheet - Page 24

• Manufacturer Part Number: AD5251
• Description: (AD5251 / AD5252) Dual 64-and 256-Position I2C Nonvolatile Memory Digital Potentiometers
• Manufacturer: Analog Devices

AD5251/AD5252
APPLICATIONS
LCD PANEL V
Large LCD panels usually require an adjustable V
centered around 6 V to 8 V with ±1 V swing and small steps
adjustment. This example represents common DAC appli-
cations where the window of adjustments is small and centered
at any level. High voltage and high resolution DACs can be used
but it is far more cost-effective to use low voltage digital
potentiometers with level shifting, such as the AD5251 or
AD5252, to achieve the objective.
Assume a V
step adjustment, as shown in Figure 44. The AD5252 can be
configured in voltage divider mode with an op amp gain. With
±20% tolerance accounted for by the AD5252, this circuit can
still be adjusted from 5 V to 7 V with an 8 mV/step in the
worst case.
CURRENT-SENSING AMPLIFIER
The dual channel, synchronous update, and channel-to-channel
resistance matching characteristics make the AD5251/AD5252
suitable for current sensing applications, such as LED
brightness control. In the circuit shown in Figure 45, when
RDAC1 and RDAC3 are programmed to the same settings, it
can be shown that
As a result, the current through a sense resistor connected
between V
circuit makes it adaptable to systems that require different sen-
sitivities. If the op amp has very low offset and low bias current,
the major source of error comes from the digital potentiometer
channel-to-channel resistance mismatch, which is typically
0.15%. The circuit accuracy is about 9 bits, which is adequate
for LED control and other general purpose applications.
Figure 44. Apply 5 V Digital Potentiometer AD5251 in a 6 V ±1 V Application.
V
+5V
o
=
2
1
and V
COM
U1
N
V
AD5252
D
DD
−
voltage requirement of 6 V ±1 V with a ±20 mV
D
18.5k
COM
350k
10k
2
(
R1
R2
R3
V
+14.4V
can be known. The programmability of this
B
2
ADJUSTMENT
−
±1%
±20%
V
1
)
+
V
R5
REF
1k
+14.4V
R4
6k
V+
V–
2.2p
C1
U2
COM
6V ± 1V
voltage
V
COM
(8)
Rev. 0 | Page 24 of 28
ADJUSTABLE HIGH POWER LED DRIVER
Figure 46 shows a circuit that can drive three to four high power
LEDs. The ADP1610 is an adjustable boost regulator that
provides adequate headroom and current for the LEDs. Because
its FB pin voltage is 1.2 V, the digital potentiometer AD5252
and the op amp form an average gain of 12 feedback networks
that servo the sensing and feedback voltages. As a result, the
voltage across R
AD5252’s setting. An adjustable LED current is
R
limit the maximum LED current. R3 should also be used in
parallel with the AD5252 to limit the LED current within an
achievable range.
+5V
SET
should be small to conserve power but large enough to
I
R
LED
SENSE
0.1kΩ
V
V
C2
10µF
1
2
=
V
R
Figure 46. High Power Adjustable LED Driver
R
R4
13.5kΩ
390pF
SET
PWM
100kΩ
U1
SET
SET
C
Figure 45. Current-Sensing Amplifier.
R
C
O
is regulated around 0.1 V, depending on the
RDAC1
RDAC3
AD5252
10kΩ
10kΩ
U2
/SD
FB
COMP
SS
B
B
10nF
ADP1610
C
SS
RT
1.1kΩ
GND
IN
SW
R2
0.1µF
U1
C8
AD8628
AD8591
+5V
V–
V+
V+
V–
+5V
L1
10µF
U1
B
U3
W
10kΩ
200Ω
U2
R3
D1
10µF
AD5252
C3
A
V
VREF
0.25kΩ
O
100Ω
R1
R
SET
D1
D2
D3
(9)
V
OUT