ADA4530-1 Datasheet, PDF (50/51 Pages) Analog Devices – Femtoampere Input Bias Current Electrometer Amplifier

Data Sheet
ADA4530-1
POWER SUPPLY RECOMMENDATIONS
Analog Devices offers a wide range of power management
products to meet the requirements of most high performance
signal chains.
Examples of a single- and dual-supply solution is shown in
Figure 133. The ADP2370 and ADP5075, cascaded with the
ADP7118 or ADM7170, and the ADP7182 generate clean
positive and negative rails. These rails power the ADA4530-1,
electrometer amplifier and/or the precision converter in a
typical signal chain.
12V
INPUT
ADP2370
BUCK
REGULATOR
+8.5V
OR +6V
+7.5V
ADP7118 ^{OR +5V}
LDO
ADP5075
INVERTING
REGULATOR
–8.5V
OR –6V
–7.5V
ADP7182 ^{OR –5V}
LDO
also be used. An LDO like the ADM7170 or ADP7118 is ideal
to generate the low noise rail.
For a dual-supply application, the ADA4530-1 typically needs a
±5 V supply, although in some applications, a ±2.5 V to ±8 V
supply can be used. LDOs like the ADP7118 or ADM7170 are the
optimum choices for the positive supply, and the ADP7182 for
the negative supply. In addition, if a negative supply is not already
available, the ADP5075 or the ADP5070 can generate the
negative supply from a positive supply, as shown in Figure 133.
Figure 134 shows the combined PSRR of using the ADP7118 to
provide +5 V on +VSY of the ADA4530-1, and the ADP7182 to
provide –5 V on–VSY, from a 9 V battery main supply. Figure 135
shows the maximum allowable ripple at the input so that the
combined PSRR of the LDO and the amplifier can still attenuate
the noise level down to the noise floor.
3.3V
INPUT
ADP5070
BOOST AND
+6V
ADP7118 ^+5V
LDO
INVERTING
REGULATOR
–6V
ADP7182 ^–5V
LDO
15V/12V/6V
INPUT
ADM7170/
ADP7118
LDO
+12V/+10V/+5V
Figure 133. Recommended Power Solutions
For example, if the main supply to the ADP7118 and ADA4530-1
has a switching noise of 20 mV p-p at 300 kHz, Figure 135 shows
that it is below the maximum value of 90 mV p-p. Therefore,
the combined PSRR of the system can still attenuate and bring
the noise level down to the noise floor, in effect, the 300 kHz
noise at the input is not seen at the output of the amplifier.
0
+PSRR
–PSRR
Table 16. Recommended Power Management Devices
–20
Product
ADP5075
ADP2370
ADP5070
ADM7170
ADP7118
ADP7182
Description
800 mA, dc-to-dc inverting regulator
High voltage, 1.2 MHz/600 kHz, 800 mA, low
quiescent current buck regulator
1 A/0.6 A, dc-to-dc switching regulator with
independent positive and negative outputs
6.5 V, 500 mA, ultralow noise, high PSRR, CMOS LDO
20 V, 200 mA, low noise, high PSRR, CMOS LDO
−28 V, −200 mA, low noise, linear regulator
POWER SUPPLY CONSIDERATIONS
–40
–60
–80
–100
–120
10k
100k
1M
10M
FREQUENCY (Hz)
The PSRR of the ADA4530-1 is excellent at dc (approximately
150 dB); however, it decreases as frequency increases. To achieve
the best performance of the ADA4530-1, a low-noise supply is
necessary. If switching supplies are used for input rails, a low
Figure 134. Positive and Negative PSRR for the ADP7118 and ADP7182
Powering ADA4530-1, ±VSY = ±5 V, +IN = 0 V
1000
ADP7118
ADP7182
dropout regulator (LDO) is essential to attenuate the switching
100
spurs to a level that does not affect the ADA4530-1 output.
Switching power supply noise typically spans a frequency range
10
from 300 kHz and up. The switching spurs can effectively be
attenuated using the LDO. Additional filtering around the LDO
may be necessary, especially when using a switching regulator to
1
generate an intermediate rail. Switching regulators also generate
high frequency noise content (>100 MHz), even when running
0.1
in the 100 kHz range, because of the high dv/dt of the switch
node. In this case, ferrite beads can be used, as described in the
AN-1120 Application Note and the AN-1368 Application Note.
0.01
0.01
0.1
1
10
FREQUENCY (Hz)
For a single-supply application, the ADA4530-1 typically needs
a 5 V, 10 V, or 12 V supply, although a 4.5 V to 16 V supply can
Figure 135. Maximum Allowable Ripple at the Input of the LDOs to Bring
Spurs To Noise Floor Level (−120 dB)
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