LTC1197CS8 datasheet(12/28 Pages) LINER

12 / 28 page

LTC1197/LTC1197L

LTC1199/LTC1199L

APPLICATI

I FOR ATIO

OVERVIEW

The LTC1197/LTC1197L/LTC1199/LTC1199L are 10-bit

switched-capacitor A/D converters. These sampling ADCs

typically draw 5mA of supply current when sampling up to

500kHz (800

µA at 2.7V sampling up to 250kHz). Supply

current drops linearly as the sample rate is reduced (see

Supply Current vs Sample Rate in the Typical Perfor-

mance Characteristics). The ADCs automatically power

down when not performing a conversion, drawing only

leakage current. They are packaged in 8-pin MSOP and SO

packages. The LTC1197L/LTC1199L operate on a single

supply ranging from 2.7V to 4V. The LTC1197 operates on

a single supply ranging from 4V to 9V while the LTC1199

operates from 4V to 6V.

These ADCs contain a 10-bit, switched-capacitor ADC, a

sample-and-hold and a serial port (see Block Diagram).

Although they share the same basic design, the LTC1197/

LTC1197L and LTC1199/LTC1199L differ in some re-

spects. The LTC1197/LTC1197L have a differential input

and have an external reference input pin. They can mea-

sure signals floating on a DC common mode voltage and

can operate with reduced spans down to 200mV. Reduc-

ing the span allows it to achieve 200

µV resolution. The

LTC1199/LTC1199L have a 2-channel input multiplexer

with the reference connected to the supply (VCC) pin. They

can convert the input voltage of either channel with re-

spect to ground or the difference between the voltages of

the two channels.

SERIAL INTERFACE

The LTC1199/LTC1199L communicate with microproces-

sors and other external circuitry via a synchronous, half

duplex, 4-wire serial interface while the LTC1197/

LTC1197L use a 3-wire interface (see Operating Sequence

in Figures 1 and 2). These interfaces are compatible with

both SPI and MICROWIRE protocols without requiring any

additional glue logic (see MICROPROCESSOR INTER-

FACES: Motorola SPI).

DATA TRANSFER

The CLK synchronizes the data transfer with each bit being

transmitted and captured on the rising CLK edge in both

transmitting and receiving systems. The LTC1199/

LTC1199L first receives input data and then transmits

back the A/D conversion result (half duplex). Because of

the half-duplex operation, DIN and DOUT may be tied

together allowing transmission over just three wires: CS,

CLK and DATA (DIN/DOUT).

Data transfer is initiated by a falling chip select (CS) signal.

After CS falls the LTC1199/LTC1199L look for a start bit on

the DIN input. After the start bit is received, the 3-bit input

word is shifted into the DIN input which configures the

LTC1199/LTC1199L and starts the conversion. After two

null bits, the result of the conversion is output on the DOUT

line in MSB-first format. At the end of the data exchange

CS should be brought high. This resets the LTC1199/

LTC1199L in preparation for the next data exchange.

Bringing CS high after the conversion also minimizes

supply current if CLK is left running.

Figure 1. LTC1197/LTC1197L Operating Sequence

1197/99 F01

CLK

tdDO

tsuCS

B0*

NULL

BITS

Hi-Z

DOUT

HI-Z

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

THE ADC WILL OUTPUT ZEROS INDEFINITELY

tCYC (14 CLKs )*

tSMPL

(1.5 CLKs)

POWER

DOWN

tCONV

(10.5 CLKs)

LTC1197CS8 Datasheet(PDF) 12 Page - Linear Technology

LTC1197CS8 Datasheet(HTML) 12 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

Datasheet Download

Link URL