LTC1450/LTC1450L
U
TYPICAL APPLICATIONS N
This application shows the LTC1450L configured as a
single supply 4-quadrant multiplying DAC. It uses a 5V
supplyandonlyoneexternalcomponent,a5kresistortied
from REFOUT to ground. (The LTC1450 can be used in a
similar fashion.) The multiplying DAC allows the user to
digitally change the amplitude and polarity of an AC input
signal whose voltage is centered around an offset signal
ground provided by the 1.22V reference voltage. The
transfer function is shown in the following equations.
1111 1111 1111
1100 0001 1001
1000 0011 0010
0100 0100 1011
0000 0110 0100
0000 0000 0000
(4094/4096)(V – V ) + V
IN REF REF
0.5(V – V ) + V
REF
IN
REF
V
REF
–0.5(V – V ) + V
IN
REF
REF
–1.0(V – V ) + V
IN
REF
REF
–1.05(V – V ) + V
REF
IN
REF
D
4096
IN
V
OUT
= (V – V
)
Gain
REF
+ 1 + V
REF
– 1
IN
(
)
For the LTC1450L Gain = 2.05 and VREF = 1.22V
VIN
1.22V ±1.15V
AT 12.5kHz
2V/DIV
1V/DIV
1V/DIV
D
4096
IN
V
OUT
= (V – 1.22V) 2.05
– 1.05 + 1.22V
IN
(
)
VOUT
DIN = 0
Table 1 shows the expressions for VOUT as a function of
VIN, VREF and DIN. The scope photo shows a 12.5kHz,
2.3VP-P triangle wave input signal and the corresponding
outputwaveformsforzero-scaleandfull-scaleDACcodes.
VOUT
DIN = 4095
1450/50L TA08
20µs/DIV
V
IN
5V
1.22V ±1.15V
REFHI
X1/X2
R
V
CC
LTC1450L
1.05R
DOUBLE-
BUFFERED
DAC
D
–
+
IN
V
OUT
WR
1.22V ±1.21V
LATCHES
12-BIT
DAC
CSMSB
CSLSB
LDAC
CLR
REFERENCE
1.22V
POWER-ON
RESET
REFOUT
REFLO
GND
1450/50L TA07
V
REF
5k
13
Linear [ Linear ]
