LTC1657 LINER [Linear Technology], LTC1657 Datasheet - Page 10

• Manufacturer Part Number: LTC1657
• Description: Parallel 16-Bit Rail-to-Rail Micropower DAC
• Manufacturer: LINER [Linear Technology]

LTC1657
TYPICAL APPLICATIO S
This circuit shows how to make a bipolar output 16-bit
DAC with a wide output swing using an LTC1657 and an
LT1077. R1 and R2 resistively divide down the LTC1657
output and an offset is summed in using the LTC1657
onboard 2.048V reference and R3 and R4. R5 ensures that
This circuit shows a digitally programmable current source
from an external voltage source using an external op amp,
an LT1218 and an NPN transistor (2N3440). Any digital
word from 0 to 65535 is loaded into the LTC1657 and its
output correspondingly swings from 0V to 4.096V. This
voltage will be forced across the resistor R
10
– 4.096
4.096
V
OUT
P
0
5:19
28
27
2
3
1
P
TRANSFER CURVE
32768
DATA (0:15)
CSLSB
CSMSB
WR
LDAC
CLR
5:19
28
27
2
3
1
X1/X2
DATA (0:15)
CSLSB
CSMSB
WR
LDAC
CLR
26
U
65535
REFLO
X1/X2
21
26
LTC1657
GND
REFHI
REFLO
A Wide Swing, Bipolar Output 16-Bit DAC
D
Digitally Programmable Current Source
LTC1657
20
IN
22
21
REFHI REFOUT
REFOUT
A
GND
. If R
22
R5
100k
1%
20
23
V
5V
V
5V
CC
CC
A
23
24
is
V
V
OUT
OUT
100k
1%
R3
0.1 F
25
25
the onboard reference is always sourcing current and
never has to sink any current even when V
scale. The LT1077 output will have a wide bipolar output
swing of – 4.096V to 4.096V as shown in the figure below.
With this output swing, 1LSB = 125 V.
chosen to be 412 , the output current will range from
0mA at zero scale to 10mA at full scale. The minimum
voltage for V
Q1’s V
voltage source can be 5V.
0.1 F
3
2
R1
100k
1%
R2
200k
1%
–
+
CESAT
LT1218
7
4
3
2
S
–
voltage. With a load resistor of 50 , the
+
LT1077
is determined by the load resistor R
5V < V
FOR R
6
– 5V
5V
7
4
S
L
200k
< 100V
Q1
2N3440
1%
R4
R
412
1%
R
50
A
L
6
I
OUT
1657 TA05
1657 TA04
V
OUT
=
(D
(65536)(R
0mA TO 10mA
:
IN
(2)(D
)(4.096)
65536
IN
)(4.096)
A
)
– 4.096V
OUT
is at full
L
and