Current-sense amplifier

01

Match common-mode range and sensing position

TI's INA240 datasheet describes a voltage-output current-sense amplifier that senses drops across shunt resistors over a common-mode range of −4 V to 80 V, independent of its 2.7–5.5 V supply. The negative range lets it work below ground during the flyback of solenoid loads, and enhanced PWM rejection suppresses large common-mode transients in motor-drive and solenoid systems; it lists 132 dB DC CMRR and 93 dB AC CMRR at 50 kHz. [1]

TI's INA181 family is specified for bidirectional low- and high-side sensing over −0.2 V to +26 V common mode; for high-side use IN− connects to the load side of the sense resistor and IN+ to the bus side, and for low-side use IN− connects to ground. [2]

Editorial note: if the shunt is in a phase or half-bridge output, the common-mode voltage swings with every PWM edge; check both the steady-state range and the AC CMRR or transient-rejection data at the switching frequency. [1]

Give the supplier the shunt position and maximum common-mode voltage (including negative excursions), PWM frequency and edge rate if any, full-scale current and shunt value, gain, unidirectional or bidirectional, supply voltage, required offset, gain error and drift, bandwidth, output type (analog or digital), package, temperature range, qualification grade and quantity.

02

Size gain, shunt and accuracy

The INA240 datasheet says the shunt is chosen from the full-scale current, the input range of the following circuit and the amplifier gain. A larger shunt voltage gives a more accurate measurement because fixed errors become a smaller share of the signal, but raises dissipation, and the resulting heat degrades accuracy through the resistor's temperature coefficient. Its 100 and 200 V/V gains with offsets below 25 µV allow smaller shunts — down to 10 mV full-scale drop. [1]

The INA240 lists gains of 20, 50, 100 and 200 V/V, 0.20% maximum gain error, 2.5 ppm/°C maximum gain drift, ±25 µV maximum offset, 250 nV/°C offset drift, 400 kHz −3 dB bandwidth, 2.4 mA maximum supply current, −40 to +125 °C operation, ±2,000 V HBM and ±1,000 V CDM ESD ratings, and 8-pin TSSOP and SOIC packages. [1] The INA181 lists ±1% maximum gain error, 1 µV/°C offset drift, 350 kHz bandwidth for the A1 gain, and 260 µA maximum supply current for the single channel. [2]

Editorial calculation: for ±20 A on an INA240A2 (50 V/V) with the output referenced to mid-supply on 5 V, a ±2.5 V swing needs ±50 mV at the shunt — 2.5 mΩ, dissipating 1 W at 20 A. The 25 µV maximum offset is then 0.05% of full scale. Halving the shunt to 1.25 mΩ with the 100 V/V version halves the dissipation and doubles the offset share to 0.1%. [1]

A linked supplier lists zero-drift bidirectional current-sense amplifiers, dual-channel high-voltage current monitors with 20 and 50 V/V gains, and power/current monitors with 16-bit I²C output. [3]

03

Trade supply current against offset and bandwidth

Renesas' ISL28006 datasheet (FN6548 Rev. 7.02, December 2022) describes a micropower unidirectional current-sense amplifier for high-side or low-side sensing, drawing 50 µA typical from a 2.7–28 V supply, with a common-mode input range of 0–28 V. It comes in fixed gains of 100, 50 and 20 V/V or an adjustable version with a minimum gain of 20, in 5-lead or 6-lead SOT-23, for −40 to +125 °C. At 25 °C with the sense input at 12 V and 20–100 mV across the shunt, offset is ±250 µV maximum at a gain of 100, but at 0.2 V common mode it widens to ±2.5 mV. Minimum CMRR is 105 dB and PSRR 90 dB, full-scale sense voltage is 200 mV, −3 dB bandwidth is 110 kHz at a gain of 100, 160 kHz at 50 and 180 kHz at 20, and ESD ratings are 4 kV HBM and 1.5 kV CDM. [4]

Editorial calculation: with 100 mV across the shunt, ±250 µV is a ±0.25% offset error, ten times the INA240's ±25 µV, and ±2.5 mV near ground is ±2.5%; the ISL28006 draws about 50 µA against the INA240's 2.4 mA maximum, which matters in battery-powered monitors. For motor or PWM control loops, the INA240's 400 kHz bandwidth is more than twice the ISL28006's 180 kHz at its lowest gain. [4] [1]

04

Compare what suppliers offer

Suppliers linked to this page list current-sense amplifiers; each card links to the page reviewed.

The listing reviewed covers analog-output current-sense amplifiers and digital power and current monitors. Ask for the datasheet with common-mode range, CMRR at your PWM frequency, gain error, offset and drift over temperature. [3]

05

Trace what each block controls

This is a functional reference built from the sources cited; it is not one maker's specification.

06

Fill the specification fields with values for your measurement

A current-sense amplifier quotation needs values for your measurement. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.

07

Send the shunt, rail and accuracy data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Position: [low side; high side; phase]
Common mode: [min/max V; PWM kHz]
Current: [full scale; uni/bidirectional]
Shunt: [mΩ; max W]
Gain: [V/V]
Accuracy: [offset µV; gain error %; drift]
Bandwidth: [kHz]
Package/grade: [package; automotive or industrial]
Quantity: [units]

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