AD7616BSTZ datasheet(26/51 Pages) AD

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Data Sheet

AD7616

Rev. 0 | Page 25 of 50

If the internal reference is to be applied elsewhere within the

system, it must first be buffered externally.

Figure 47. Reference Circuitry

SHUTDOWN MODE

The AD7616 enters shutdown mode by keeping the RESET pin

low for greater than 1.2 µs. When the RESET pin is set from low

to high, the device exits shutdown mode and enters normal

mode.

When the AD7616 is placed in shutdown mode, the current

consumption is typically 78 µA and the power-up time to

perform a write to the device is approximately 240 µs. Power-up

time to perform a conversion is 15 ms. In shutdown mode, all

circuitry is powered down and all registers are cleared and reset

to their default values.

DIGITAL FILTER

The AD7616 contains an optional digital first-order sinc filter

for use in applications where slower throughput rates are in use

or where higher SNR or dynamic range is desirable.

The OSR of the digital filter is controlled in hardware using the

oversampling pins, OS2 to OS0 (OSx), or in software via the OS

bits within the configuration register. In software mode, over-

sampling is enabled for all channels after the OS bits are set in

the configuration register. In hardware mode, the OSx signals at

the time a full reset is released determine the OSR to be used.

Table 9 provides the oversampling bit decoding to select the

different oversample rates. In addition to the oversampling

function, the output result is decimated to 16-bit resolution.

If the OSx pins/OS bits are set to select an OS ratio of eight, the

next CONVST rising edge takes the first sample for the selected

channel, and the remaining seven samples for that channel are

taken with an internally generated sampling signal. These

samples are then averaged to yield an improvement in SNR

performance. As the OS ratio increases, the −3 dB frequency is

reduced, and the allowed sampling frequency is also reduced.

The conversion time extends as the oversampling rate is increased,

and the BUSY signal scales with oversampling rates. Acquisition

and conversion time increase linearly with oversampling ratio.

If oversampling is enabled with the sequencer or in burst mode,

the extra samples are gathered for a given channel before the

sequencer moves on to the next channel.

Table 9 shows the typical SNR performance of the device for

each permissible oversampling ratio. The input tone used was a

100 Hz sine wave for the three input ranges of the device. A plot

of SNR vs. OSR is shown in Figure 48.

Figure 48. Typical SNR vs. OSR for all Analog Input Ranges

Table 9. Oversampling Bit Decoding

OSx Pins/OS Bits

OSR

Typical SNR (dB)

−3 dB Bandwidth (kHz)

±2.5 V Range

±5 V Range

±10 V Range

All Ranges

000

No oversampling

87.5

89.7

90.8

001

88.1

90.6

91.8

36.5

010

91.6

92.9

011

89.9

92.6

93.9

30.5

100

93.6

94.9

101

92.6

94.8

95.8

13.2

110

93.9

95.5

96.2

7.2

111

128

94.4

95.4

95.9

3.6

BUF

2.5V

REF

REFINOUT

REFSEL

REFINOUTGND

REFCAP

100nF

10µF

100

OSR

±2.5V RANGE

±5V RANGE

±10V RANGE

fIN = 100Hz

120

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