LTC1196 datasheet(16/28 Pages) LINER

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LTC1196/LTC1198

APPLICATI

I FOR ATIO

Dummy Bits

The last 2 bits of the input word following the MUX

Address are dummy bits. Either bit can be a “logical

one” or a “logical zero.” These 2 bits allow the ADC 2.5

clocks to acquire the input signal after the channel

selection.

A/D Conversion Result

Both the LTC1196 and the LTC1198 have the A/D

conversion result appear on the DOUT line after two null

bits (see Operating Sequence in Figures 1 and 2). Data

on the DOUT line is updated on the rising edge of the CLK

line. The DOUT data should also be captured on the

rising CLK edge by the digital systems. Data on the DOUT

line remains valid for a minimum time of thDO (30ns at

5V) to allow the capture to occur (see Figure 3).

Figure 3. Voltage Waveform for DOUT Delay Time,

tdDO and thDO

Unipolar Transfer Curve

The LTC1196/LTC1198 are permanently configured for

unipolar only. The input span and code assignment for

this conversion type are shown in the following figures.

Unipolar Transfer Curve

Unipolar Output Code

OUTPUT CODE

1 1 1 1 1 1 1 1

1 1 1 1 1 1 1 0

•

0 0 0 0 0 0 0 1

0 0 0 0 0 0 0 0

INPUT VOLTAGE

VREF – 1LSB

VREF – 2LSB

•

1LSB

INPUT VOLTAGE

(VREF = 5.000V)

4.9805V

4.9609V

•

0.0195V

1196/98 AI05

Operation with DIN and DOUT Tied Together

The LTC1198 can be operated with DIN and DOUT tied

together. This eliminates one of the lines required to

communicate to the digital systems. Data is transmitted in

both directions on a single wire. The pin of the digital

systems connected to this data line should be configurable

as either an input or an output. The LTC1198 will take

control of the data line and drive it low on the 5th falling

CLK edge after the start bit is received (see Figure 4).

Therefore the port line of the digital systems must be

switched to an input before this happens to avoid a

conflict.

REDUCING POWER CONSUMPTION

The LTC1196/LTC1198 can sample at up to a 1MHz rate,

drawing only 50mW from a 5V supply. Power consump-

tion can be reduced in two ways. Using a 3V supply lowers

the power consumption on both devices by a factor of five,

to 10mW. The LTC1198 can reduce power even further

because it shuts down whenever it is not converting.

Figure 5 shows the supply current versus sample rate for

the LTC1196 and LTC1198 on 3V and 5V. To achieve such

a low power consumption, especially for the LTC1198,

several things must be taken into consideration.

Shutdown (LTC1198)

Figure 2 shows the operating sequence of the LTC1198.

The converter draws power when the CS pin is low and

powers itself down when that pin is high. For lowest power

consumption in shutdown, the CS pin should be driven

with CMOS levels (0V to VCC) so that the CS input buffer

of the converter will not draw current.

VIN

0 0 0 0 0 0 0 1

0 0 0 0 0 0 0 0

1 1 1 1 1 1 1 1

1 1 1 1 1 1 1 0

•

1196/98 AI04

CLK

DOUT

tdDO

1196/98 TC03

VIH

thDO

VOH

VOL

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