Datasheet

ADA4898-1/ADA4898-2 Data Sheet
THEORY OF OPERATION
The ADA4898-1/ADA4898-2 are voltage feedback op amps that
combine unity gain stability with 0.9 nV/√Hz input noise. They
employ a highly linear input stage that can maintain greater
than −90 dBc (at 2 V p-p) distortion out to 600 kHz while in a
unity-gain configuration. This rare combination of unity gain
stability, low input-referred noise, and extremely low distortion
is the result of Analog Devices, Inc., proprietary op amp
architecture and high voltage bipolar processing technology.
The simplified ADA4898-1/ADA4898-2 topology, shown in
Figure 44, is a single gain stage with a unity-gain output buffer. It
has over 100 dB of open-loop gain and maintains precision
specifications, such as CMRR, PSRR, and offset, to levels that are
normally associated with topologies having two or more gain
stages.
BUFFERg
m
C
C
R1 R
L
V
OUT
07037-041
Figure 44. Topology
PD
(POWER-DOWN) PIN FOR THE ADA4898-1
The
PD
pin saves power by decreasing the quiescent power
dissipated in the device. It is very useful when power is an issue
and the device does not need to be turned on at all times. The
response of the device is rapid when going from power-down
mode to full power operation mode. Note that
PD
does not put
the output in a high-Z state, which means that the
ADA4898-1/
ADA4898-2 are not recommended for use as multiplexers.
Leaving the
PD
pin floating keeps the amplifier in full power
operation mode.
Table 7. Power-Down Voltage Control
PD
Pin
±15 V ±10 V ±5 V
Power-Down Mode ≤−14 V ≤−9 V ≤−4 V
Rev. E | Page 14 of 20
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