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LTC1598

4- and 8-Channel, Micropower Sampling 12-Bit Serial I/O A/D Converters

Linear Technology 

LTC1594/LTC1598

APPLICATIONS INFORMATION

OVERVIEW

The LTC1594/LTC1598 are micropower, 12-bit sampling

A/D converters that feature a 4- and 8-channel multi-

plexer respectively. They typically draw only 320μA of

supply current when sampling at 16.8kHz. Supply cur-

rent drops linearly as the sample rate is reduced (see

Supply Current vs Sample Rate). The ADCs automatically

power down when not performing conversions, drawing

only leakage current. The LTC1594 is available in a 16-pin

narrow SO package and the LTC1598 is packaged in a

24-pin SSOP. Both devices operate on a single supply

from 4.5V to 5.5V.

The LTC1594/LTC1598 contain a 12-bit, switched-

capacitor ADC, sample-and-hold, serial port and an

external reference input pin. In addition, the LTC1594 has

a 4-channel multiplexer and the LTC1598 provides an

8-channel multiplexer (see Block Diagram). They can

measure signals floating on a DC common mode voltage

and can operate with reduced spans to 1.5V. Reducing

the spans allow them to achieve 366μV resolution.

The LTC1594/LTC1598 provide separate MUX output

and ADC input pins to form an ideal MUXOUT/ADCIN

loop which economizes signal conditioning. The MUX

and ADC of the devices can also be controlled individually

through separate chip selects to enhance flexibility.

SERIAL INTERFACE

For this discussion we will assume that CSMUX and

CSADC are tied together and will refer to them as simply

CS, unless otherwise specified.

The LTC1594/LTC1598 communicate with the micropro-

cessor and other external circuitry via a synchronous,

half duplex, 4-wire interface (see Operating Sequences in

Figures 1 and 2).

CSMUX = CSADC = CS

CLK

tCYC

tsuCS

DIN

DOUT

CH0 TO

CH7

ADCIN =

MUXOUT

COM = GND

EN

D1

DON’T CARE

D2

D0

NULL

Hi-Z

BIT

B11 B10 B9

B8

B7

B6

B5

B4

B3 B2

B1 B0*

Hi-Z

tSMPL

tCONV

tON

*AFTER COMPLETING THE DATA TRANSFER, IF FURTHER CLOCKS ARE APPLIED WITH CS LOW,

THE ADC WILL OUTPUT LSB-FIRST DATA THEN FOLLOWED WITH ZEROS INDEFINITELY

1594/98 F01

Figure 1. LTC1594/LTC1598 Operating Sequence Example: CH2, GND

15948fb

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