ADAQ7980 datasheet(32/49 Pages) AD

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ADAQ7980/ADAQ7988

Data Sheet

Rev. 0 | Page 32 of 49

SAMPLING FREQUENCY = 100kHz

tS = 10µs

ACQUISITION

SHUTDOWN

3µs

POWERED

SHUTDOWN

Vf1

tTURNOFF1

Vf2

tTURNOFF2

tAMP, ON

Vf3

tf3

tTURNOFF3

ADC

MODE

CNV

PD_AMP

CONVERSION

MINIMUM

POWERED ON TIME = 3µs

ADC DRIVER

OUTPUT

Figure 63. Timing Waveforms

Figure 64 shows the quiescent power of the ADC driver with

and without the power scaling. Without power scaling, the

amplifier constantly consumes power regardless of the sampling

frequency, as shown in the following equation.

PQ = IQ × VS

With power scaling, the quiescent power becomes proportional

to the ratio of the amplifier on time (tAMP, ON) and the sampling

time (tS).

PQ = IQ × VS × (tAMP, ON/tS)

Thus, by dynamically switching the driver between shutdown

and full power modes during the sample period, the quiescent

power of the driver scales with the sampling rate.

1.2

1.0

0.4

0.8

0.2

0.6

11M

100k

100

10k

SAMPLING FREQUENCY (

fS)

AMP QUIESCENT CURRENT NO DPS

AMP QUIESCENT CURRENT WITH DPS

ADC CURRENT DRAW

PD_AMP ON

TIME = 3µs

V+ = 5V

V– = 0V

Figure 64. Quiescent Current of the ADC Driver vs. ADC Sampling Frequency

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