Datasheet

AD5623R/AD5643R/AD5663R Data Sheet
Rev. E | Page 26 of 32
APPLICATIONS INFORMATION
USING A REFERENCE AS A POWER SUPPLY
Because the supply current required by the AD5623R/AD5643R/
AD5663R is extremely low, an alternative option is to use a
voltage reference to supply the required voltage to the parts (see
Figure 60). This is especially useful if the power supply is quite
noisy or if the system supply voltages are at some value other
than 5 V or 3 V, for example, 15 V. The voltage reference outputs
a steady supply voltage for the AD5623R/AD5643R/ AD5663R.
If the low dropout REF195 is used, it must supply 500 µA of
current to the AD5623R/AD5643R/AD5663R, with no load on
the output of the DAC. When the DAC output is loaded, the
REF195 also needs to supply the current to the load. The total
current required (with a 5 kΩ load on the DAC output) is
500 µA + (5 V/5 kΩ) = 1.25 mA
The load regulation of the REF195 is typically 2 ppm/mA,
which results in a 3 ppm (15 µV) error for the 1.5 mA current
drawn from it. This corresponds to a 0.196 LSB error.
AD5623R/
AD5643R/
AD5663R
THREE-WIRE
SERIAL
INTERFACE
SYNC
SCLK
DIN
15V
5V
V
OUT
= 0V TO 5V
V
DD
REF195
05858-041
Figure 60. REF195 as Power Supply to the AD5623R/AD5643R/AD5663R
BIPOLAR OPERATION USING THE AD5663R
The AD5663R has been designed for single-supply operation,
but a bipolar output range is also possible using the circuit in
Figure 61. The circuit gives an output voltage range of ±5 V.
Rail-to-rail operation at the amplifier output is achievable using
an AD820 or an OP295 as the output amplifier.
The output voltage for any input code can be calculated as
follows:












×−






+
×






×=
R1
R2
V
R1
R2R1D
VV
DDDD
O
536,65
where D represents the input code in decimal (0 to 65,535).
With V
DD
= 5 V, R1 = R2 = 10 kΩ,
V5
536,65
10
−






×
=
D
V
O
This is an output voltage range of ±5 V, with 0x0000 corre-
sponding to a −5 V output, and 0xFFFF corresponding to a
+5 V output.
THREE-WIRE
SERIAL
INTERFACE
R2 = 10kΩ
+5V
–5V
AD820/
OP295
+5V
AD5663R
V
DD
V
OUT
R1 = 10kΩ
±5V
0.1µF10µF
05858-042
Figure 61. Bipolar Operation with the AD5663R
USING THE AD5663R WITH A
GALVANICALLY ISOLATED INTERFACE
In process control applications in industrial environments,
it is often necessary to use a galvanically isolated interface to
protect and isolate the controlling circuitry from any hazardous
common-mode voltages that can occur in the area where
the DAC is functioning. iCoupler® provides isolation in excess
of 2.5 kV. The AD5663R uses a 3-wire serial logic interface, so
the ADuM1300 3-channel digital isolator provides the required
isolation (see Figure 62). The power supply to the part also
needs to be isolated, which is done by using a transformer. On
the DAC side of the transformer, a 5 V regulator provides the
5 V supply required for the AD5663R.
0.1µF
5V
REGULATOR
GND
DIN
SYNC
SCLK
POWER
10µF
SDI
SCLK
DATA
AD5663R
V
OUT
V
OB
V
OA
V
OC
V
DD
V
IC
V
IB
V
IA
ADuM1300
05858-043
Figure 62. AD5663R with a Galvanically Isolated Interface