AD7983 datasheet(18/24 Pages) AD

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AD7625

Data Sheet

Rev. A | Page 18 of 24

POWER SUPPLY

The AD7625 uses both 5 V (VDD1) and 2.5 V (VDD2) power

supplies, as well as a digital input/output interface supply (VIO).

VIO allows a direct interface with 2.5 V logic only. VIO and

VDD2 can be taken from the same 2.5 V source; however, it is

best practice to isolate the VIO and VDD2 pins using separate

traces and also to decouple each pin separately.

The 5 V and 2.5 V supplies required for the AD7625 can be

generated using Analog Devices, Inc., low dropout regulators

(LDOs) such as the ADP3330-2.5, ADP3330-5, ADP3334, and

ADP1708.

100

10k

VDD2

VDD1

SUPPLY FREQUENCY (Hz)

INTERNAL REFERENCE USED

Figure 26. PSRR vs. Supply Frequency

(350 mV pp Ripple on VDD2, 600 mV Ripple on VDD1)

Power-Up

When powering up the AD7625 device, first apply the VIO

voltage to the device so that the EN1 and EN0 values can be set

for the reference option in use. Connect the EN0 and EN1 pins

to pull-up/pull-down resistors to ensure that one or both of

these pins is set to a nonzero value. EN0 = 0 and EN1 = 0 is an

illegal state that must be avoided.

After VIO is established, apply the 2.5 V VDD2 supply to the

device followed by the 5 V VDD1 supply and then an external

reference (depending on the reference setting being used).

Finally, apply the analog inputs to the ADC.

SAMPLING RATE (kSPS)

1000

2000

3000

4000

5000

6000

7000

VDD2 INTERNAL REF

VDD2 EXTERNAL REF

VDD1 EXTERNAL REF

VDD1 INTERNAL REF

VIO

Figure 27. Current Consumption vs. Sampling Rate

SAMPLING RATE (kSPS)

1000

2000

3000

4000

5000

6000

7000

100

110

120

130

140

150

INTERNAL REF

EXTERNAL REF

Figure 28. Power Dissipation vs. Sampling Rate

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