REV. C

–10–

AD7713

PGA Gain

G2

Gl

G0

Gain

0

0

0

1

(Default Condition After the Internal Power-On Reset)

00

1

2

01

0

4

01

1

8

10

0

16

10

1

32

11

0

64

1

1

1

128

Channel Selection

CH1 CH0 Channel

0

0

AIN1

(Default Condition After the Internal Power-On Reset)

0

1

AIN2

1

0

AIN3

Word Length

WL

Output Word Length

0

16-Bit

(Default Condition After Internal Power-On Reset)

1

24-Bit

RTD Excitation Currents

RO

0

Off

(Default Condition After Internal Power-On Reset)

1On

Burn-Out Current

BO

0

Off

(Default Condition After Internal Power-On Reset)

1On

Bipolar/Unipolar Selection (Both Inputs)

B/U

0

Bipolar

(Default Condition After Internal Power-On Reset)

1

Unipolar

Filter Selection (FS11–FS0)

The on-chip digital filter provides a Sinc

the filter cutoff frequency, the position of the first notch of the filter and the data rate for the part. In association with the gain selec-

tion, it also determines the output noise (and hence the effective resolution) of the device.

2 MHz, this results in a first notch frequency range from 1.952 Hz to 205.59 kHz. To ensure correct operation of the AD7713, the

value of the code loaded to these bits must be within this range. Failure to do this will result in unspecified operation of the device.

Changing the filter notch frequency, as well as the selected gain, impacts resolution. Tables I and II and Figure 2 show the effect of

the filter notch frequency and gain on the effective resolution of the AD7713. The output data rate (or effective conversion time) for

the device is equal to the frequency selected for the first notch of the filter. For example, if the first notch of the filter is selected at

10 Hz, then a new word is available at a 10 Hz rate or every 100 ms. If the first notch is at 200 Hz, a new word is available every 5 ms.

The settling time of the filter to a full-scale step input change is worst case 4

× 1/(output data rate). This settling time is to 100% of

the final value. For example, with the first filter notch at 100 Hz, the settling time of the filter to a full-scale step input change is

400 ms max. If the first notch is at 200 Hz, the settling time of the filter to a full-scale input step is 20 ms max. This settling time

can be reduced to 3

× l/(output data rate) by synchronizing the step input change to a reset of the digital filter. In other words, if the

step input takes place with SYNC low, the settling time will be 3

× l/(output data rate). If a change of channels takes place, the set-

tling time is 3

× l/(output data rate) regardless of the SYNC input.

The –3 dB frequency is determined by the programmed first notch frequency according to the relationship: filter –3 dB frequency

= 0.262

× first notch frequency.