13
LTC1450/LTC1450L
TYPICAL APPLICATIONS N
U
4-Quadrant Multiplying DAC Application
This application shows the LTC1450L configured as a
single supply 4-quadrant multiplying DAC. It uses a 5V
supply and only one external component, a 5k resistor tied
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.
V
OUT
= (V
IN
– V
REF
)
+ V
REF
Gain + 1
– 1
()
D
IN
4096
For the LTC1450L Gain = 2.05 and V
REF
= 1.22V
V
OUT
= (V
IN
– 1.22V)
+ 1.22V2.05 – 1.05
()
D
IN
4096
Table 1 shows the expressions for V
OUT
as a function of
V
IN
, V
REF
and D
IN
. The scope photo shows a 12.5kHz,
2.3V
P-P
triangle wave input signal and the corresponding
output waveforms for zero-scale and full-scale DAC codes.
Table 1. Binary Code Table for 4-Quadrant, Multiplying DAC
Application
BINARY DIGITAL
INPUT CODE IN
DAC REGISTER ANALOG OUTPUT (V
OUT
)
MSB LSB
1111 1111 1111 (4094/4096)(V
IN
– V
REF
) + V
REF
1100 0001 1001 0.5(V
IN
– V
REF
) + V
REF
1000 0011 0010 V
REF
0100 0100 1011 –0.5(V
IN
– V
REF
) + V
REF
0000 0110 0100 –1.0(V
IN
– V
REF
) + V
REF
0000 0000 0000 –1.05(V
IN
– V
REF
) + V
REF
5k
GND
LTC1450L
5V
V
OUT
1.22V ±1.21V
12-BIT
DAC
REFHI
REFLOREFOUT
V
REF
D
IN
CLR
V
IN
1.22V ±1.15V
V
CC
R 1.05R
X1/X2
1450/50L TA07
–
+
DOUBLE-
BUFFERED
DAC
LATCHES
POWER-ON
RESET
REFERENCE
1.22V
WR
CSMSB
CSLSB
LDAC
Clean 4-Quadrant Multiplying Is Shown in the Output
Waveforms for Zero-Scale and Full-Scale DAC Settings
1V/DIV
2V/DIV
1V/DIV
V
OUT
D
IN
= 0
V
OUT
D
IN
= 4095
V
IN
1.22V ±1.15V
AT 12.5kHz
20µs/DIV
Internal Reference, REFLO/REFHI Pins, Gain Adjust and Wide Supply Voltage Range
Allow 4-Quadrant Mulitplying on a 5V Single Supply
1450/50L TA08
