Datasheet

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.
50
55
60
65
70
75
80
85
90
1 10 100 1k 10k
VDD2
VDD1
07652-011
SUPPLY FREQUENCY (Hz)
PSRR (dB)
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.
07652-016
SAMPLING RATE (kSPS)
CURRENT (mA)
0
5
10
15
20
25
0 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
07652-017
SAMPLING RATE (kSPS)
POWER DISSIPATION (mW)
0 1000 2000 3000 4000 5000 6000 7000
60
70
80
90
100
110
120
130
140
150
INTERNAL REF
EXTERNAL REF
Figure 28. Power Dissipation vs. Sampling Rate