ADA4896-2ACP-EBZ AD [Analog Devices], ADA4896-2ACP-EBZ Datasheet - Page 17

• Manufacturer Part Number: ADA4896-2ACP-EBZ
• Description: 1 nV/?Hz, Low Power
• Manufacturer: AD [Analog Devices]

Data Sheet
THEORY OF OPERATION
AMPLIFIER DESCRIPTION
The
noise amplifiers that consume 3 mA from supplies ranging from
3 V to 10 V. Fabricated on the Analog Devices SiGe bipolar process,
the
excess of 200 MHz. The amplifiers are unity-gain stable, and the
input structure results in an extremely low input 1/f noise for a
high speed amplifier.
The rail-to-rail output stage is designed to drive the heavy feed-
back load required to achieve an overall low output referred noise.
To meet more demanding system requirements, the large signal
bandwidth of the
increased beyond the typical fundamental limits of other low noise,
unity-gain stable amplifiers. The maximum offset voltage of 500 μV
and drift of 0.2 μV/°C make the ADA4896-2/ADA4897-1/
ADA4897-2
performance is not needed because there is minimal power
penalty in achieving the low input noise or the high bandwidth.
INPUT PROTECTION
The
from ESD events, withstanding human body model ESD events
of 2.5 kV and charged-device model events of 1 kV with no mea-
sured performance degradation. The precision input is protected
with an ESD network between the power supplies and diode
clamps across the input device pair, as shown in Figure 44.
For differential voltages above approximately 0.7 V, the diode
clamps begin to conduct. Too much current can cause damage
due to excessive heating. If large differential voltages must be
sustained across the input terminals, it is recommended that the
current through the input clamps be limited to less than 10 mA.
Series input resistors that are sized appropriately for the expected
differential overvoltage provide the needed protection.
ADA4896-2/ADA4897-1/ADA4897-2
ADA4896-2/ADA4897-1/ADA4897-2
ADA4896-2/ADA4897-1/ADA4897-2
excellent amplifier choices even when the low noise
Figure 44. Input Stage and Protection Diodes
+IN
+V
–V
ESD
ESD
TO THE REST OF THE AMPLIFIER
S
S
ADA4896-2/ADA4897-1/ADA4897-2
BIAS
ESD
ESD
have a bandwidth in
are 1 nV/√Hz input
are fully protected
–IN
was
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B
The ESD clamps begin to conduct for input voltages that are
more than 0.7 V above the positive supply and input voltages
more than 0.7 V below the negative supply. If an overvoltage
condition is expected, it is recommended that the input current
be limited to less than 10 mA.
DISABLE OPERATION
Figure 45 shows the
circuitry. If the DISABLE pin is left unconnected, the base of
the input PNP transistor is pulled high through the internal
pull-up resistor to the positive supply and the part is turned
on. Pulling the DISABLE pin to ≥2 V below the positive supply
turns the part off, reducing the supply current to approximately
18 μA for a 5 V voltage supply.
The DISABLE pin is protected by ESD clamps, as shown in
Figure 45. Voltages beyond the power supplies cause these
diodes to conduct. For protection of the DISABLE pin, the
voltage to this pin should not exceed 0.7 V above the positive
supply or 0.7 V below the negative supply. If an overvoltage
condition is expected, it is recommended that the input current
be limited with a series resistor to less than 10 mA.
When the amplifier is disabled, its output goes to a high
impedance state. The output impedance decreases as frequency
increases; this effect can be observed in Figure 36. In disable
mode, a forward isolation of 50 dB can be achieved at 10 MHz.
Figure 43 shows the forward isolation vs. frequency data.
+V
–V
ADA4896-2/ADA4897-1/ADA4897-2
S
S
ADA4897-1/ADA4897-2
Figure 45. DISABLE Circuit
I
BIAS
AMPLIFIER
BIAS
TO
ESD
ESD
DISABLE
power-down