10

LTC1594/LTC1598

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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 320

μA 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 366

μV 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).

CLK

EN

D1

D2

CSMUX = CSADC = CS

B5

B6

B7

B8

B9

B10

B11

Hi-Z

CH0 TO

CH7

Hi-Z

NULL

BIT

D0

B4

B3

B2

B1 B0*

DON’T CARE

ADCIN =

MUXOUT

COM = GND

*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