LTC1450L View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC1450L' PDF : 16 Pages View PDF
LTC1450/LTC1450L
TYPICAL APPLICATIONS N
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.
( ) VOUT = (VIN – VREF)
Gain
DIN
4096
–1
+1
+ VREF
For the LTC1450L Gain = 2.05 and VREF = 1.22V
( ) VOUT = (VIN – 1.22V)
2.05
DIN
4096
– 1.05
+ 1.22V
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
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
MSB
LSB
ANALOG OUTPUT (VOUT)
1111 1111 1111
1100 0001 1001
1000 0011 0010
0100 0100 1011
0000 0110 0100
0000 0000 0000
(4094/4096)(VIN – VREF) + VREF
0.5(VIN – VREF) + VREF
VREF
– 0.5(VIN – VREF) + VREF
– 1.0(VIN – VREF) + VREF
– 1.05(VIN – VREF) + VREF
Clean 4-Quadrant Multiplying Is Shown in the Output
Waveforms for Zero-Scale and Full-Scale DAC Settings
VIN
1.22V ±1.15V
AT 12.5kHz
2V/DIV
VOUT
DIN = 0
1V/DIV
VOUT
DIN = 4095
1V/DIV
20µs/DIV
1450/50L TA08
Internal Reference, REFLO/REFHI Pins, Gain Adjust and Wide Supply Voltage Range
Allow 4-Quadrant Mulitplying on a 5V Single Supply
VIN
1.22V ±1.15V
REFHI
5V
X1/X2
R
VCC LTC1450L
1.05R
DIN
DOUBLE-
BUFFERED
WR
DAC
CSMSB LATCHES
CSLSB
LDAC
12-BIT
DAC
CLR POWER-ON
RESET
REFERENCE
1.22V
REFOUT
REFLO
VREF
5k
–
VOUT
1.22V ±1.21V
+
GND
1450/50L TA07
13
Share Link: 
