Download

PDF Abstract Text:

Micropower ADC and DAC in SO-8 Give PCs a 12-Bit Analog Interface ­ Design Note 138

Kevin R. Hoskins

advertisement
Micropower ADC and DAC in SO-8 Give PCs a 12-Bit Analog Interface - Design Note 138
Kevin R. Hoskins
Introduction Adding two channels of analog input / output to a PC computer is simple, inexpensive, low powered and compact when using the LTC®1298 ADC and LTC1446 DAC. The LTC1298 and the LTC1446 are the first SO-8 packaged 2-channel devices of their kind. While the application shown is for PC data acquisition, the two converters provide the smallest, lowest power solutions for many other analog I / O applications. Small, Micropower ADC and DAC The LTC1298 features a 12-bit ADC, 2-channel multiplexer, and an input S / H. Operating on a 5V supply at maximum conversion rate, the LTC1298 draws just 340µA. A built-in auto shutdown further reduces power dissipation at reduced sampling rates (to 30µA at 1ksps). The serial interface allows remote operation. The LTC1446 is the first 12-bit dual micropower SO-8 packaged DAC. It features a 1mV / LSB (0V to 4.095V) railto-rail output, internal 2.048V reference and a simple, cost-effective, 3-wire serial interface. A DOUT pin allows cascading multiple LTC1446s without increasing the number of serial interconnections. Operating on a supply of 5V, the LTC1446 draws just 1mA (typ).
U1 LTC1298 D1 510 INPUT 1 INPUT 2 510 D3 D2 1 510 2 3 CS CH0 VCC CLK DOUT DIN 8 7 6 5 4 3 2 1 51k SELECT 5 51k DIN 13 51k SCLK DOUT TX C1 0.1µF 2 4 3
, LTC and LT are registered trademarks of Linear Technology Corporation.
C4 150µF
CH1 510 4 GND D4
U2 LTC1446 1 2 3 4 AOUT1 AOUT2 D1 TO D6: 1N914 CLK DIN CS / LD DOUT VOUTB VCC GND VOUTA 8 7 6 5 C2 0.1µF 12 10 11
11 5V C3 0.1µF
DN138 F01
Figure 1. Communicating Over the Serial Port, the LTC1298 and LTC1446 in SO-8 Create a Simple, Low Power 2-Channel Analog Interface for PCs
Conclusion These SO-8 packaged data converters offer unprecedented space, power and economy to data acquisition system designers. They form a very nice 12-bit analog interface to a wide variety of portable, battery-powered and size constrained products. They are extremely easy to apply and require a minimum of passive support components and interconnections.
Listing 1. Configure Analog Interface with this C Code
For literature on our Data Conversion products, call 1-800-4-LINEAR. For applications help, call (408) 432-1900, Ext. 2453
LT / GP 0996 155K · PRINTED IN THE USA
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 q FAX: (408) 434-0507 q TELEX: 499-3977