OPA992 datasheet(28/50 Pages) TI

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The load current (ILOAD) produces a voltage drop across the shunt resistor (RSHUNT). The load current is set

from 0 A to 1 A. To keep the shunt voltage below 100 mV at maximum load current, the largest shunt resistor is

defined using Equation 2:

RSHUNT = VSHUNT_MAX

ILOAD_MAX = 100 mV1 A = 100 mΩ

(2)

Using Equation 2, RSHUNT is calculated to be 100 mΩ. The voltage drop produced by ILOAD and RSHUNT is

amplified by the OPA992-Q1 to produce an output voltage of 0 V to 4.9 V. The gain needed by the OPA992-Q1

to produce the necessary output voltage is calculated using Equation 3:

Gain = VOUT_MAX − VOUT_MIN

VIN_MAX − VIN_MIN

(3)

Using Equation 3, the required gain is calculated to be 49 V/V, which is set with resistors RF and RG. Equation 4

is used to size the resistors, RF and RG, to set the gain of the OPA992-Q1 to 49 V/V.

Gain = 1 + RFRG

(4)

Choosing RF as 5.76 kΩ, RG is calculated to be 120 Ω. RF and RG were chosen as 5.76 kΩ and 120 Ω because

the values are standard value resistors that create a 49:1 ratio. Other resistors that create a 49:1 ratio can also

be used. However, excessively large resistors generate thermal noise that exceeds the intrinsic noise of the op

amp. Figure 8-2 shows the measured transfer function of the circuit shown in Figure 8-1.

8.2.1.3 Application Curve

ILOAD (A)

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

Figure 8-2. Low-Side, Current-Sense, Transfer Function

8.3 Power Supply Recommendations

The OPAx992-Q1 is specified for operation from 2.7 V to 40 V (±1.35 V to ±20 V); many specifications apply

from –40°C to 125°C or with specific supply voltages and test conditions.

CAUTION

Supply voltages larger than 40 V can permanently damage the device; see Section 6.1.

Place 0.1-µF bypass capacitors close to the power-supply pins to reduce errors coupling in from noisy or

high-impedance power supplies. For more detailed information on bypass capacitor placement, refer to Section

8.4.

OPA992-Q1, OPA2992-Q1, OPA4992-Q1

SBOSAC9D – AUGUST 2022 – REVISED APRIL 2023

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