LTC1197CS8 datasheet(14/28 Pages) LINER

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LTC1197/LTC1197L

LTC1199/LTC1199L

APPLICATI

I FOR ATIO

Dummy Bit

The dummy bit is a placeholder that extends the acquisi-

tion time of the ADC. This bit can be either high or low and

does not affect the conversion of the ADC.

Operation with DIN and DOUT Tied Together

The LTC1199/LTC1199L can be operated with DIN and

DOUT tied together. This eliminates one of the lines

required to communicate to the microprocessor (MPU).

Data is transmitted in both directions on a single wire. The

processor pin connected to this data line should be

configurable as either an input or an output. The LTC1199/

LTC1199L will take control of the data line and drive it low

on the 4th falling CLK edge after the start bit is received

(see Figure 3). Therefore the processor port line must be

switched to an input before this happens to avoid a

conflict.

In the Typical Applications section, there is an example of

interfacing the LTC1199/LTC1199L with DIN and DOUT

tied together to the Intel 8051 MPU.

Unipolar Transfer Curve

The LTC1197/LTC1197L/LTC1199/LTC1199L are perma-

nently configured for unipolar only. The input span and

code assignment for this conversion type are shown in the

following figures for a 5V reference.

CLK

DATA (DIN/DOUT)

START

SGL/DIFF

ODD/SIGN

DUMMY

NULL BITS

LTC1199/LTC1199L CONTROL DATA LINE

AND SEND A/D RESULT BACK TO MPU

MPU CONTROLS DATA LINE AND SENDS

MUX ADDRESS TO LTC1199/LTC1199L

PROCESSOR MUST RELEASE

DATA LINE AFTER 4TH RISING CLK

AND BEFORE THE 4TH FALLING CLK

LTC1199/LTC1199L TAKE CONTROL OF

DATA LINE ON 4TH FALLING CLK

1197/99 F03

Figure 3. LTC1199/LTC1199L Operation with DIN and DOUT Tied Together

Unipolar Transfer Curve

VIN

0 0 0 0 0 0 0 0 0 1

0 0 0 0 0 0 0 0 0 0

1 1 1 1 1 1 1 1 1 1

1 1 1 1 1 1 1 1 1 0

•

1197/99 AI03

Unipolar Output Code

OUTPUT CODE

1 1 1 1 1 1 1 1 1 1

1 1 1 1 1 1 1 1 1 0

•

0 0 0 0 0 0 0 0 0 1

0 0 0 0 0 0 0 0 0 0

INPUT VOLTAGE

VREF – 1LSB

VREF – 2LSB

•

1LSB

INPUT VOLTAGE

(VREF = 5.000V)

4.99512V

4.99023V

•

4.88mV

1197/99 AI04

ACHIEVING MICROPOWER PERFORMANCE

With typical operating currents of 5mA (LTC1197/

LTC1199) at 5V and 0.8mA (LTC1197L/LTC1199L) at

2.7V it is possible for these ADCs to achieve true

micropower performance by taking advantage of the

automatic shutdown between conversions. In systems

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