AD7816ARM datasheet(14/20 Pages) AD

14 / 20 page

REV. C

–14–

AD7816/AD7817/AD7818

DB7 – DB0

DB7(DB9) – DB0

DOUT

CONVST

SCLK

BUSY

RD/

DIN

OTI

t17

t15

t16

Figure 16. Mode 1 Operation

TIME – secs

0.8

–0.01

016

0.5

0.2

0.7

0.4

0.0

AIR

0.6

0.3

0.1

FLUID

HEAT SINK

Figure 14. Self-Heating Effect in Air, Fluid, and in Thermal

Contact with a Heat Sink

TIME – secs

0.25

–0.05

0.0

2.0

0.5

1.5

0.15

0.05

0.10

0.00

AIR

1.0

FLUID

HEATSINK

0.20

Figure 15. Self-Heating Effect in Air, Fluid, and in Thermal

Contact with a Heat Sink

OPERATING MODES

The AD7816, AD7817, and AD7818 have two possible modes

of operation depending on the state of the

CONVST pulse at

the end of a conversion.

Mode 1

In this mode of operation the

CONVST pulse is brought high

before the end of a conversion, i.e., before the BUSY goes low

(see Figure 16). When operating in this mode a new conversion

should not be initiated until 100 ns after the end of a serial read

operation. This quiet time is to allow the track/hold to accu-

rately acquire the input signal after a serial read.

Mode 2

When the AD7816, AD7817, and AD7818 are operated in Mode

2 (see Figure 17), they automatically power down at the end of

a conversion. The

CONVST is brought low to initiate a conver-

sion and is left logic low until after the end of the conversion. At

this point, i.e., when BUSY goes low, the devices will power-

down. The devices are powered up again on the rising edge of

the

CONVST signal. Superior power performance can be

achieved in this mode of operation by powering up the AD7816,

AD7817, and AD7818 only to carry out a conversion (see Power

vs. Throughput section). In Figure 17 the

CS line is applicable

to the AD7817 only.

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