Datasheet

AD5546/AD5556 Data Sheet
Rev. D | Page 12 of 20
APPLICATIONS INFORMATION
UNIPOLAR MODE
Two-Quadrant Multiplying Mode, V
OUT
= 0 V to –V
REF
The AD5546/AD5556 DAC architecture uses a current-steering
R-2R ladder design that requires an external reference and op
amp to convert the unipolar mode of output voltage to
AD5546
V
OUT
= –V
REF
× D/65,536 (1)
AD5556
V
OUT
= –V
REF
× D/16,384 (2)
where D is the decimal equivalent of the input code.
The output voltage polarity is opposite to the V
REF
polarity in
this case (see Figure 19). Table 8 shows the negative output vs.
code for the AD5546.
Table 8. AD5546 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
Two-Quadrant Multiplying Mode, V
OUT
= 0 V to +V
REF
The AD5546/AD5556 are designed to operate with either
positive or negative reference voltages. As a result, positive
output can be achieved with an additional op amp, (see
Figure 20), and the output becomes
AD5546
V
OUT
= +V
REF
× D/65,536 (3)
AD5556
V
OUT
= +V
REF
× D/16,384 (4)
Table 9 shows the positive output vs. code for the AD5546.
Table 9. AD5546 Unipolar Mode Positive 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
03810-021
2
+5V
5
4
G
ND
V
IN
TRIM
U3
ADR03
V
OUT
V
DD
R1
R
OFS
R
OFS
VOUT
–2.5V TO 0V
R
FB
R
FB
C6
2.2pF
GND
U1
AD5546/AD5556
I
OUT
R2
C4
0.1µF
C5
1µF
R
COM
R1
16-/14-BIT
DATA
16-/14-BIT
DATA
REF
U2
AD8628
–
+
–5V
WR
WR
LDAC
LDAC
RS
RS
MSB
MSB
C2
0.1µF
C1
1µF
C3
0.1µF
V+
V–
Figure 19. Unipolar Two-Quadrant Multiplying Mode, V
OUT
= 0 to –V
REF