AD7883

REV. 0

–10–

POWER-DOWN CONTROL (MODE INPUT)

The AD7883 is designed for systems which need to have mini-

mum power consumption. This includes such applications as

hand held, portable battery powered systems and remote moni-

toring systems. As well as consuming minimum power under

normal operating conditions, typically 8 mW, the AD7883 can

be put into a power-down or sleep mode when not required to

convert signals. When in this power-down mode, the AD7883

consumes 1 mW of power.

The AD7883 is powered down by bringing the MODE input

pin to a Logic Low in conjunction with keeping the RD input

control High. The AD7883 will remain in the power-down

mode until MODE is brought to a Logic High again. The

MODE input should be driven with CD4000 or HCMOS logic

levels.

It is recommended that one “dummy” conversion be imple-

mented before reading conversion data from the AD7883 after it

has been in the powerdown mode. This is required to reset all

internal logic and control circuitry. Allow one clock cycle before

doing the dummy conversion. In a remote monitoring system

where, say, 10 conversions are required to be taken with a sam-

pling interval of 1 second, an additional 11th conversion must

be carried out. Figure 14 gives a plot of power consumption as a

function of time for such operation. The total conversion time

for each cycle is 11

× 20 µs (where 20 µs is the time taken for a

single conversion) corresponding to 2.2

0

1

2

TIME – secs

POWER

CONSUMPTION

– mW

8

1

CONVERTING

POWER-DOWN

CONVERTING

POWER-DOWN

2.2 x 10

–4

Figure 14. Power Consumption for Normal Operation and

Power-Down Operation vs. Time

Hence:

Average Power

= {8 mW

+ {1 mW

× (0.9998)}

= 1.0015 mW