ltc1590cs-trpbf Linear Technology Corporation, ltc1590cs-trpbf Datasheet - Page 8

• Manufacturer Part Number: ltc1590cs-trpbf
• Description: Ltc1590 - Dual Serial 12-bit Multiplying Dac
• Manufacturer: Linear Technology Corporation

APPLICATIONS
LTC1590
Unipolar 2-Quadrant Multiplying Mode
(V
The LTC1590 can be used with a dual op amp to provide
a dual 2-quadrant multiplying DAC as shown in Figure 2.
The unipolar DAC transfer function is shown in Table 1.
The 33pF feedback capacitor is recommended to compen-
sate for the pole caused by the internal feedback resistor
and the OUT1 output capacitance. For high speed op amps
this feedback capacitor is required for stability, and a
smaller value, 8pF to 15pF, may be desired to get the
fastest transient response and shortest settling time. A
larger feedback capacitor can be used to reduce wideband
noise, glitch impulse and distortion for lower frequency
signals. A pole is introduced in the DAC transfer function
at approximately (C
back capacitor will typically give a pole at:
8
OUT
145
Figure 2. Unipolar Operation (2-Quadrant Multiplication)
0.1 F
= 0V to – V
kHz
V
5V
CC
DAC A OR DAC B
DGND
–10V TO 10V
LTC1590
V
V
2 100
REF
REF
AGND
5V
REF
R
U
FB
OUT2
OUT1
FB
)
pF
)(R
–10V TO 10V
1
0.1 F
INFORMATION
FB
11
U
V
). For example, a 100pF feed-
V
k
CC
DAC A OR DAC B
REF
DGND
33pF
LTC1590
V
REF
–
+
AGND
Figure 3. Bipolar Operation (4-Quadrant Multiplication)
LT1112
W
–15V
1/2
15V
R
FB
OUT2
OUT1
U
V
0V TO –V
OUT
33pF
20k
R2
1590 F02
–
+
REF
LT1112
1/2
–15V
15V
Table 1. Unipolar Binary Code Table
Bipolar 4-Quadrant Multiplying Mode
(V
The circuit of Figure 3 can be used to provide a dual
4-quadrant multiplying DAC. This circuit starts with the
unipolar application circuit and adds three resistors and an
op amp. These extra devices provide a gain of – 2 from the
unipolar output to the bipolar output, plus an offset of
(–1)(V
2. A pack of matched 20k resistors, with two resistors in
parallel forming the 10k resistor, is recommended.
Table 2. Bipolar Offset Binary Code Table
OUT
1111 1111 1111
1000 0000 0000
0000 0000 0001
0000 0000 0000
1111 1111 1111
1000 0000 0001
1000 0000 0000
0111 1111 1111
0000 0000 0000
MSB
MSB
= – V
IN DAC REGISTER
REF
IN DAC REGISTER
BINARY NUMBER
BINARY NUMBER
DIGITAL INPUT
DIGITAL INPUT
10k
R1
) to produce the transfer function shown in Table
REF
to +V
LSB
LSB
–
+
LT1112
1/2
–15V
REF
20k
15V
R3
)
– V
– V
– V
0V
+V
+V
0V
– V
– V
REF
REF
REF
REF
REF
REF
REF
ANALOG OUTPUT
ANALOG OUTPUT
V
–V
(2047/2048)
(1/2048)
(4095/4096)
(2048/4096) = – V
(1/4096)
(1/2048)
(2048/2048) = – V
OUT
REF
TO V
V
V
1590 F03
OUT
OUT
REF
REF
REF
/2