ADA4254 datasheet(24/29 Pages) AD

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ADA4523-1

Data Sheet

Rev. 0 | Page 24 of 29

SHUTDOWN MODE

The ADA4523-1 features a shutdown mode for low power

applications. In the off state, both amplifiers are shut off and

draw less than 20 µA (maximum over temperature) of supply

current per amplifier. In addition, in the off stage, both outputs

present high impedances to external circuitry.

Keep in mind that during the off state, even with the amplifier

output in high impedance, the output can still modulate by the

input signal through the input differential clamp and the

feedback resistor. (See Figure 64 for the location of the

differential clamp.) In addition, depending on the resistor

values, significant current can still be drawn from the input

source.

Shutdown control is accomplished using the separate logic SD

reference voltage input (SDCOM) and the shutdown pin (SD).

This method allows low voltage digital control logic to operate

independently of the high voltage supply rails of the op amp. A

summary of the shutdown control logic and operating ranges is

shown in Table 8 and Table 9.

Table 8. Shutdown Control Logic

Shutdown Pin Condition

Amplifier State

SD = float, SDCOM = float

SD − SDCOM ≥ 2 V

SD − SDCOM ≤ 0.8 V

Off

Table 9. Operating Voltage Range for Shutdown Pins

Mnemonic

Minimum

Maximum

SD − SDCOM

−0.2 V

+5.2 V

SDCOM

V−

V+ − 2.35 V

V−

V+

If the shutdown feature is not required, leave SD and SDCOM

floating. Internal circuitry automatically keeps the amplifier in

the on state.

For operation in noisy environments, adding a capacitor

between SD and SDCOM is recommended to prevent noise

from changing the shutdown state.

When there is a danger of SD and SDCOM pulling beyond the

supply rails, adding resistance in series with the shutdown pins

is recommended to limit current.

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