LTC1450LIN datasheet(13/16 Pages) LINER

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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)

+ VREF

Gain

+ 1

– 1

()

DIN

4096

For the LTC1450L Gain = 2.05 and VREF = 1.22V

VOUT = (VIN – 1.22V)

+ 1.22V

2.05

– 1.05

()

DIN

4096

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

ANALOG OUTPUT (VOUT)

MSB

LSB

1111 1111 1111

(4094/4096)(VIN – VREF) + VREF

1100 0001 1001

0.5(VIN – VREF) + VREF

1000 0011 0010

VREF

0100 0100 1011

– 0.5(VIN – VREF) + VREF

0000 0110 0100

– 1.0(VIN – VREF) + VREF

0000 0000 0000

– 1.05(VIN – VREF) + VREF

GND

LTC1450L

VOUT

1.22V

±1.21V

12-BIT

DAC

REFHI

REFLO

REFOUT

VREF

DIN

CLR

VIN

1.22V

±1.15V

VCC

1.05R

X1/X2

1450/50L TA07

–

DOUBLE-

BUFFERED

DAC

LATCHES

POWER-ON

RESET

REFERENCE

1.22V

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

VOUT

DIN = 0

VOUT

DIN = 4095

VIN

1.22V

±1.15V

AT 12.5kHz

µs/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

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