Data Sheet

AD8628/AD8629/AD8630

FUNCTIONAL DESCRIPTION

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Rev. M | 17 of 21

Figure 60. Negative Input Overload Recovery for Competitor A

Figure 61. Negative Input Overload Recovery for Competitor B

The results shown in Figure 56 to Figure 61 are summarized in

Table 5.

Table 5. Overload Recovery Time

Model

Positive Overload

Recovery (µs)

Negative Overload

Recovery (µs)

AD8628

6

9

Competitor A

650

25,000

Competitor B

40,000

35,000

INFRARED SENSORS

Infrared (IR) sensors, particularly thermopiles, are increasingly be-

ing used in temperature measurement for applications as wide

ranging as automotive climate control, human ear thermometers,

home insulation analysis, and automotive repair diagnostics. The

relatively small output signal of the sensor demands high gain with

very low offset voltage and drift to avoid dc errors.

If interstage ac coupling is used, as in Figure 62, low offset and

drift prevent the output of the input amplifier from drifting close

to saturation. The low input bias currents generate minimal errors

from the output impedance of the sensor. As with pressure sensors,

the very low amplifier drift with time and temperature eliminate

additional errors once the temperature measurement is calibrated.

The low 1/f noise improves SNR for dc measurements taken over

periods often exceeding one-fifth of a second.

Figure 62 shows a circuit that can amplify ac signals from 100 µV

to 300 µV up to the 1 V to 3 V levels, with a gain of 10,000 for

accurate analog-to-digital conversion.

Figure 62. AD8629 Used as Preamplifier for Thermopile

PRECISION CURRENT SHUNT SENSOR

A precision current shunt sensor benefits from the unique attributes

of auto-zero amplifiers when used in a differencing configuration, as

shown in Figure 63. Current shunt sensors are used in precision

current sources for feedback control systems. They are also used in

a variety of other applications, including battery fuel gauging, laser

diode power measurement and control, torque feedback controls in

electric power steering, and precision power metering.

Figure 63. Low-Side Current Sensing

In such applications, it is desirable to use a shunt with very low re-

sistance to minimize the series voltage drop; this minimizes wasted

power and allows the measurement of high currents while saving

power. A typical shunt might be 0.1 Ω. At measured current values

of 1 A, the output signal of the shunt is hundreds of millivolts, or

even volts, and amplifier error sources are not critical. However,

at low measured current values in the 1 mA range, the 100 µV

output voltage of the shunt demands a very low offset voltage and

drift to maintain absolute accuracy. Low input bias currents are also

needed, so that injected bias current does not become a significant

percentage of the measured current. High open-loop gain, CMRR,