INA849 datasheet(29/52 Pages) TI

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Output Current (mA)

-1

-40 C

25 C

85 C

125 C

VClamp+/-

Figure 8-13. Output Voltage With Output Clamping Enabled

The VCLAMP+ pin features a fail-safe against power-up sequencing issues between the INA851 and a

downstream device. For example, a condition of V(CLAMP+) + 10 V on this pin does not cause damage.

Therefore, the ADC supply can safely turn on while the INA851 supply is still off or just beginning to turn

on. In this case, the current draw through the VCLAMP+ pin is limited to a safe value of typically 3 mA.

8.3.6 Low Noise

An output noise calculation helps design a low-noise circuit to drive high-precision ADC applications and

optimize the signal-to-noise ratio (SNR).

Figure 8-14 shows a simplified noise model for the INA851. The eNO noise refers to the input resistor network of

the FDA. This term incorporates the thermal noise of the internal feedback resistors, and the interaction of the

internal current noise density of the output stage with the internal feedback resistors.

GIN

GOUT

eNI

eNO(GOUT = 1 or GOUT = 0.2)

eN(RTO)

eN(RTI)

Figure 8-14. Simplified Noise Model for the INA851

The internal feedback resistor network is considered in the eNO specification; therefore, the calculation of the

total input-referred noise, eN(RTI), is simplified to the following equation:

eNRTI = eNI2+ eNOGOUT=1 or GOUT=0.2

GIN

(4)

The total output-referred noise, eN(RTO), multiplies directly by the output stage gain, GOUT, by GOUT = 0.2 V/V or

GOUT = 1 V/V respectively, as shown in the following equation:

eNRTO = eNI×GIN×0.2 V/V or 1 V/V2+ eNOGOUT=1 or GOUT=0.2 ×0.2 V/V or 1 V/V2

(5)

8.4 Device Functional Modes

The INA851 has a single functional mode and operates when the power-supply voltage is greater than 8 V

(±4 V). The maximum power-supply voltage for the INA851 is 36 V (±18 V).

www.ti.com

INA851

SBOS999A – MARCH 2022 – REVISED OCTOBER 2022

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