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.

BUFFER

gm

CC

R1

RL

VOUT

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