Datasheet

AD5547/AD5557 Data Sheet
Rev. D | Page 14 of 20
APPLICATIONS INFORMATION
UNIPOLAR MODE
2-Quadrant Multiplying Mode, V
OUT
= 0 V to –V
REF
The AD5547/AD5557 DAC architecture uses a current-steering
R-2R ladder design that requires an external reference and op
amp to convert the unipolar mode of the output voltage to
V
OUT
= −V
REF
× D/65,536 (AD5547) (1)
V
OUT
= −V
REF
× D/16,384 (AD5557) (2)
where D is the decimal equivalent of the input code.
In this case, the output voltage polarity is opposite the V
REF
polarity (see Figure 21). Table 7 shows the negative output vs.
code for the AD5547.
Table 7. AD5547 Unipolar Mode Negative Output vs. Code
D in Binary V
OUT
(V)
1111 1111 1111 1111 –V
REF
(65,535/65,536)
1000 0000 0000 0000 –V
REF
/2
0000 0000 0000 0001 –V
REF
(1/65,536)
0000 0000 0000 0000 0
WR
WR
RS
RS
2
LDAC
+2.5V
04452-007
AD8628
AD5547/AD5557
R
1A
16/14 DATA
VDD
R
COMA
R2
U1
R1
R
OFSA
R
FBA
C6
RFBROFS
MSB A0, A1
I
OUTA
AGNDA
6.8pF
C1
1µF
C2
0.1µF
C3
0.1µF
V
OUTA
V
REFA
MSB
A0, A1
LDAC
+V
–V
GND
4
V
OUT
TRIM
ADR03
5
6
V
IN
U3
2
+5V
16-/14-BIT
2.5V
C4
1µF
0.1µF
C5
–5V
–2.5V TO 0V
Figure 21. Unipolar 2-Quadrant Multiplying Mode, V
OUT
= 0 to –V
REF