AD7617 datasheet(25/52 Pages) AD

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AD7617

Data Sheet

Rev. 0 | Page 24 of 51

If there is no corresponding resistor on the VxAGND or

VxBGND channel, an offset error occurs on that channel. Use

the input overvoltage clamp protection circuitry to protect the

AD7617 against transient overvoltage events. It is not recom-

mended to leave the AD7617 in a condition where the clamp

protection circuitry is active in normal or power-down

conditions for extended periods.

Figure 44. Input Resistance Matching on the Analog Input

Analog Input Antialiasing Filter

An analog antialiasing filter (a first-order Butterworth) is also

provided on the AD7617. Figure 45 and Figure 46 show the

frequency and phase response, respectively, of the analog

antialiasing filter. The typical corner frequency in the ±10 V

range is 39 kHz, and 33 kHz in the ±5 V range.

Figure 45. Analog Antialiasing Filter Frequency Response

Figure 46. Analog Antialiasing Filter Phase Response

ADC TRANSFER FUNCTION

The output coding of the AD7617 is twos complement. The code

transitions occur midway between successive integer LSB values,

that is, 1/2 LSB and 3/2 LSB. The LSB size is full-scale range ÷

16,384 for the AD7617. The ideal transfer characteristics for the

AD7617 are shown in Figure 47 and Figure 9. The LSB size is

dependent on the analog input range selected.

Figure 47. Transfer Characteristics

Table 9.

Range

+FS

Midscale

−FS

LSB

±10 V

+10 V

0 V

−10 V

+1220 μV

±5 V

+5 V

0 V

−5 V

+610 μV

±2.5 V

+2.5 V

0 V

−2.5 V

+305 μV

INTERNAL/EXTERNAL REFERENCE

The AD7617 can operate with either an internal or external

reference. The device contains an on-chip 2.5 V band gap refer-

ence. The REFINOUT pin allows access to the 2.5 V reference

that generates the on-chip 4.096 V reference internally, or it allows

an external reference of 2.5 V to be applied to the AD7617. An

externally applied reference of 2.5 V is also amplified to 4.096 V

using the internal buffer. This 4.096 V buffered reference is the

reference used by the SAR ADC.

The REFSEL pin is a logic input pin that allows the user to select

between the internal reference and an external reference. If this

pin is set to logic high, the internal reference is selected and

enabled. If this pin is set to logic low, the internal reference is

disabled, and an external reference voltage must be applied

to the REFINOUT pin.

The internal reference buffer is always enabled. After a full reset,

the AD7617 operates in the reference mode selected by the

REFSEL pin. Decoupling is required on the REFINOUT pin for

both the internal and external reference options. A 100 nF, X7R

ceramic capacitor is required on the REFINOUT pin to

REFINOUTGND.

1MΩ

CLAMP

Vxx

1MΩ

CLAMP

VxxGND

RFB

ANALOG

INPUT

SIGNAL

AD7617

–30

–25

–20

–15

–10

–5

100

10k

100k

INPUT FREQUENCY (Hz)

±10V RANGE

±5V RANGE

±2.5V RANGE

100

10k

100k

INPUT FREQUENCY (Hz)

±10V RANGE

±5V RANGE

±2.5V RANGE

011...111

011...110

000...001

000...000

111...111

100...010

100...001

100...000

–FS + 1/2LSB 0V – 1/2LSB +FS – 3/2LSB

ANALOG INPUT

+FS – (–FS)

2N*

*WHERE N IS THE NUMBER OF BITS OF THE CONVERTER

LSB =

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