The INA281-Q1 is a high-precision current sense amplifier that can measure voltage drops across shunt resistors over a wide common-mode range from –4 V to 110 V. The negative common-mode voltage allows the device to operate below ground, thus accommodating precise measurement of recirculating currents in half-bridge applications. The combination of a low offset voltage, small gain error and high DC CMRR enables highly accurate current measurement. The INA281-Q1 is not only designed for DC current measurement, but also for high-speed applications (like fast overcurrent protection, for example) with a high bandwidth of 1.3 MHz and an 65-dB AC CMRR (at 50 kHz).
The INA281-Q1 operates from a single 2.7-V to 20-V supply, drawing 1.5 mA of supply current. The INA281-Q1 is available with five gain options: 20 V/V, 50 V/V, 100 V/V, 200 V/V, and 500 V/V. These gain options address wide dynamic range for current-sensing applications.
The INA281-Q1 is specified over an operating temperature range of −40 °C to +125 °C and is offered in a space-saving SOT-23 package with two pin-out variants.
PART NUMBER | PACKAGE(1) | BODY SIZE (NOM) |
---|---|---|
INA281INA281-Q1 | SOT-23 (5) | 2.90 mm × 1.60 mm |
PIN | TYPE | DESCRIPTION | ||
---|---|---|---|---|
NAME | INA281A | INA281B | ||
GND | 2 | 2 | Ground | Ground |
IN– | 4 | 5 | Input | Shunt resistor negative sense input |
IN+ | 3 | 4 | Input | Shunt resistor positive sense input |
OUT | 1 | 1 | Output | Output voltage |
Vs | 5 | 3 | Power | Power supply |
MIN | MAX | UNIT | ||
---|---|---|---|---|
Supply Voltage (VS) | –0.3 | 22 | V | |
Analog Inputs, VIN+, VIN– (2) | Differential (VIN+) – (VIN–), INA281A5, INA281B5 | –6 | 6 | V |
Differential (VIN+) – (VIN–), All others | –12 | 12 | ||
Common-mode | –20 | 120 | ||
Output | GND – 0.3 | VS + 0.3 | V | |
TA | Operating temperature | –55 | 150 | °C |
TJ | Junction temperature | 150 | °C | |
Tstg | Storage temperature | –65 | 150 | °C |
VALUE | UNIT | |||
---|---|---|---|---|
V(ESD) | Electrostatic discharge | Human body model (HBM), per ANSI/ESDA/JEDEC JS-001, all pins(1) | ±2000 | V |
Charged device model (CDM), per JEDEC specification JESD22-C101, all pins(2) | ±1000 |
MIN | NOM | MAX | UNIT | ||
---|---|---|---|---|---|
VCM | Common-mode input range | –4 | 48 | 110 | V |
VS | Operating supply range | 2.7 | 5 | 20 | V |
VSENSE | Differential sense input range | 0 | VS / G | V | |
TA | Ambient temperature | –40 | 125 | °C |
THERMAL METRIC(1) | INA281 | UNIT | |
---|---|---|---|
DBV (SOT-23) | |||
5 PINS | |||
RθJA | Junction-to-ambient thermal resistance | 184.7 | °C/W |
RθJC(top) | Junction-to-case (top) thermal resistance | 105.6 | °C/W |
RθJB | Junction-to-board thermal resistance | 47.2 | °C/W |
ΨJT | Junction-to-top characterization parameter | 21.5 | °C/W |
ΨJB | Junction-to-board characterization parameter | 46.9 | °C/W |
RθJC(bot) | Junction-to-case (bottom) thermal resistance | N/A | °C/W |
PARAMETER | TEST CONDITIONS | MIN | TYP | MAX | UNIT | |
---|---|---|---|---|---|---|
INPUT | ||||||
VCM | Common-mode input range(1) | TA = –40 °C to +125 °C | –4 | 110 | V | |
CMRR | Common-mode rejection ratio, input referred | –4 V ≤ VCM ≤ 110 V, TA = –40 °C to +125 °C | 120 | 140 | dB | |
f = 50 kHz | 65 | dB | ||||
Vos | Offset voltage, input referred | INA281x1 | ±100 | ±500 | µV | |
INA281x2 | ±55 | ±300 | ||||
INA281x3 | ±30 | ±250 | ||||
INA281x4 | ±30 | ±200 | ||||
INA281x5 | ±15 | ±150 | ||||
dVos/dT | Offset voltage drift | TA = –40 ℃ to +125 ℃ | ±0.1 | ±1 | µV/℃ | |
PSRR | Power supply rejection ratio, input referred | 2.7 V ≤ VS ≤ 20 V, TA = –40 °C to +125 °C |
±1.5 | ±10 | µV/V | |
IB | Input bias current | IB+, VSENSE = 0 V | 10 | 20 | 30 | uA |
IB–, VSENSE = 0 V | 10 | 20 | 30 | uA | ||
OUTPUT | ||||||
G | Gain | INA281x1 | 20 | V/V | ||
INA281x2 | 50 | V/V | ||||
INA281x3 | 100 | V/V | ||||
INA281x4 | 200 | V/V | ||||
INA281x5 | 500 | V/V | ||||
GERR | Gain error | GND + 50 mV ≤ VOUT ≤ VS – 200 mV | ±0.07 | ±0.5 | % | |
TA = –40 °C to +125 °C | ±2 | ±20 | ppm/°C | |||
NLERR | Nonlinearity error | 0.01 | % | |||
Maximum capacitive load | No sustained oscillations, no isolation resistor | 500 | pF | |||
VOLTAGE OUTPUT | ||||||
Swing to Vs (Power supply rail) | RLOAD = 10 kΩ, TA = –40 °C to +125 °C | VS – 0.07 | VS – 0.15 | V | ||
Swing to ground | RLOAD = 10 kΩ, VSENSE = 0 V, TA = –40 °C to +125 °C | 0.005 | 0.02 | V | ||
FREQUENCY RESPONSE | ||||||
BW | Bandwidth | INA281x1, CLOAD = 5 pF, VSENSE = 200 mV |
1300 | kHz | ||
INA281x2, CLOAD = 5 pF, VSENSE = 80 mV |
1300 | |||||
INA281x3, CLOAD = 5 pF, VSENSE = 40 mV |
1000 | |||||
INA281x4, CLOAD = 5 pF, VSENSE = 20 mV |
900 | |||||
INA281x5, CLOAD = 5 pF, VSENSE = 8 mV |
900 | |||||
SR | Slew rate | Rising edge | 2.5 | V/µs | ||
Settling time | VOUT = 4 V ± 0.1 V step, Output settles to 0.5% | 10 | µs | |||
VOUT = 4 V ± 0.1 V step, Output settles to 1% | 5 | |||||
VOUT = 4 V ± 0.1 V step, Output settles to 5% | 1 | |||||
NOISE | ||||||
Ven | Voltage noise density | 50 | nV/√Hz | |||
POWER SUPPLY | ||||||
Vs | Supply voltage | TA = –40 °C to +125 °C | 2.7 | 20 | V | |
IQ | Quiescent current | 1.5 | 2 | mA | ||
TA = –40 °C to +125 °C | 2.25 | mA |
All specifications at TA = 25 °C, VS = 5 V, VSENSE = VIN+ – VIN– = 0.5 V / Gain, VCM = VIN– = 48 V, unless otherwise noted.
VSENSE = 0 V |
VS = 5 V |
VS = 2.7 V |
VS = 20 V |
The INA281-Q1 is a high- or low-side current-sense amplifier that offers a wide common-mode range, precision zero-drift topology, excellent common-mode rejection ratio (CMRR), high bandwidth, and fast slew rate. Different gain versions are available to optimize the output dynamic range based on the application. The INA281-Q1 is designed using a transconductance architecture with a current-feedback amplifier that enables low bias currents of 20 µA with a common-mode voltage of 110 V.
The INA281-Q1 supports large input common-mode voltages from –4 V to +110 V. Because of the internal topology, the common-mode range is not restricted by the power-supply voltage (VS). This allows for the INA281-Q1 to be used for both low- and high-side current-sensing applications.
The INA281-Q1 –3-dB bandwidth is gain-dependent, with several gain options of 20 V/V, 50 V/V, 100 V/V, 200 V/V, and 500 V/V. The unique multistage design enables the amplifier to achieve high bandwidth at all gains. This high bandwidth provides the throughput and fast response that is required for the rapid detection and processing of overcurrent events.
The bandwidth of the device also depends on the applied VSENSE voltage. Figure 6-1 shows the bandwidth performance profile of the device over frequency as output voltage increases for each gain variation. As shown in Figure 6-1, the device exhibits the highest bandwidth with higher VSENSE voltages, and the bandwidth is higher with lower device gain options. Individual requirements determine the acceptable limits of error for high-frequency, current-sensing applications. Testing and evaluation in the end application or circuit is required to determine the acceptance criteria and validate whether or not the performance levels meet the system specifications.
The INA281-Q1 inputs draw a 20-µA (typical) bias current at a common-mode voltage as high as 110 V, which enables precision current sensing on applications that require lower current leakage.
The INA281-Q1 operates with high performance across the entire valid VSENSE range. The zero-drift input architecture of the INA281-Q1 provides the low offset voltage and low offset drift needed to measure low VSENSE levels accurately across the wide operating temperature of –40 °C to +125 °C. Low VSENSE operation is particularly beneficial when using low ohmic shunts for low current measurements, as power losses across the shunt are significantly reduced.
The INA281-Q1 gain error is < 0.5% at room temperature, with a maximum drift of 20 ppm/°C over the full temperature range of –40 °C to +125 °C. TheINA281-Q1 is available in multiple gain options of 20 V/V, 50 V/V, 100 V/V, 200 V/V, and 500 V/V, which the system designer should select based on their desired signal-to-noise ratio and other system requirements.
The INA281-Q1 closed-loop gain is set by a precision, low-drift internal resistor network. The ratio of these resistors are excellently matched, while the absolute values may vary significantly. TI does not recommend adding additional resistance around the INA281-Q1 to change the effective gain because of this variation, however. The typical values of the gain resistors are described in Table 6-1.
GAIN | R1 | RL |
---|---|---|
20 (V/V) | 25 kΩ | 500 kΩ |
50 (V/V) | 10 kΩ | 500 kΩ |
100 (V/V) | 10 kΩ | 1000 kΩ |
200 (V/V) | 5 kΩ | 1000 kΩ |
500 (V/V) | 2 kΩ | 1000 kΩ |
The INA281-Q1 operates with a wide supply range from 2.7 V to 20 V. The output stage supports a wide output range, while the INA281-Q1x1 (gain of 20 V/V) at a supply voltage of 20 V allows a maximum acceptable differential input of 1 V. When paired with the small input offset voltage of the INA281-Q1, systems with very wide dynamic ranges of current measurement can be supported.
The INA281-Q1 measures the differential voltage developed by current flowing through a resistor that is commonly referred to as a current-sensing resistor or a current-shunt resistor. The INA281-Q1 operates in unidirectional mode only, meaning it only senses current sourced from a power supply to a system load as shown in Figure 6-2.
The linear range of the output stage is limited to how close the output voltage can approach ground under zero-input conditions. The zero current output voltage of the INA281-Q1 is very small, with a maximum of GND + 20 mV. Make sure to apply a differential input voltage of (20 mV / Gain) or greater to keep the INA281-Q1 output in the linear region of operation.
With a bandwidth of 1.3 MHz at a gain of 20 V/V and a slew rate of 2.5 V/µs, the INA281-Q1 is specifically designed for detecting and protecting applications from fast inrush currents. As shown in Table 6-2, the INA281-Q1 responds in less than 2 µs for a system measuring a 75-A threshold on a 2-mΩ shunt.
PARAMETER | EQUATION | INA281-Q1 AT VS = 5 V | |
---|---|---|---|
G | Gain | 20 V/V | |
IMAX | Maximum current | 100 A | |
IThreshold | Threshold current | 75 A | |
RSENSE | Current sense resistor value | 2 mΩ | |
VOUT_MAX | Output voltage at maximum current | VOUT_MAX = IMAX × RSENSE × G | 4 V |
VOUT_THR | Output voltage at threshold current | VOUT_THR = ITHR × RSENSE × G | 3 V |
SR | Slew rate | 2.5 V/µs | |
Output response time | Tresponse= VOUT_THR / SR | < 2 µs |
Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes, as well as validating and testing their design implementation to confirm system functionality.
The INA281-Q1 amplifies the voltage developed across a current-sensing resistor as current flows through the resistor to the load. The wide input common-mode voltage range and high common-mode rejection of the INA281-Q1 make it usable over a wide range of voltage rails while still maintaining an accurate current measurement.
The accuracy of any current-sense amplifier is maximized by choosing the current-sense resistor to be as large as possible. A large sense resistor maximizes the differential input signal for a given amount of current flow and reduces the error contribution of the offset voltage. However, there are practical limits as to how large the current-sense resistor can be in a given application because of the resistor size and maximum allowable power dissipation. Equation 1 gives the maximum value for the current-sense resistor for a given power dissipation budget:
where:
An additional limitation on the size of the current-sense resistor and device gain is due to the power-supply voltage, VS, and device swing-to-rail limitations. To make sure that the current-sense signal is properly passed to the output, both positive and negative output swing limitations must be examined. Equation 2 provides the maximum values of RSENSE and GAIN to keep the device from exceeding the positive swing limitation.
where:
To avoid positive output swing limitations when selecting the value of RSENSE, there is always a trade-off between the value of the sense resistor and the gain of the device under consideration. If the sense resistor selected for the maximum power dissipation is too large, then it is possible to select a lower-gain device to avoid positive swing limitations.
The negative swing limitation places a limit on how small the sense resistor value can be for a given application. Equation 3 provides the limit on the minimum value of the sense resistor.
where:
Table 7-1 shows an example of the different results obtained from using five different gain versions of the INA281-Q1. From the table data, the highest gain device allows a smaller current-shunt resistor and decreased power dissipation in the element.
PARAMETER | EQUATION | RESULTS AT VS = 5 V | |||||
---|---|---|---|---|---|---|---|
A1, B1 DEVICES | A2, B2 DEVICES | A3, B3 DEVICES | A4, B4 DEVICES | A5, B5 DEVICES | |||
G | Gain | 20 V/V | 50 V/V | 100 V/V | 200 V/V | 500 V/V | |
VDIFF | Ideal differential input voltage | VDIFF = VOUT / G | 250 mV | 100 mV | 50 mV | 25 mV | 10 mV |
RSENSE | Current sense resistor value | RSENSE = VDIFF / IMAX | 25 mΩ | 10 mΩ | 5 mΩ | 2.5 mΩ | 1 mΩ |
PSENSE | Current-sense resistor power dissipation | RSENSE × IMAX2 | 2.5 W | 1 W | 0.5W | 0.25 W | 0.1 W |
Input filters are not required for accurate measurements using the INA281-Q1INA281, and use of filters in this location is not recommended. If filter components are used on the input of the amplifier, follow the guidelines in this section to minimize the effects on performance.
Based strictly on user design requirements, external filtering of the current signal may be desired. The initial location that can be considered for the filter is at the output of the current-sense amplifier. Although placing the filter at the output satisfies the filtering requirements, this location changes the low output impedance measured by any circuitry connected to the output voltage pin. The other location for filter placement is at the current-sense amplifier input pins. This location also satisfies the filtering requirement, but the components must be carefully selected to minimally impact device performance. Figure 7-1 shows a filter placed at the input pins.
External series resistance provides a source of additional measurement error, so keep the value of these series resistors to 10 Ω or less to reduce loss of accuracy. The internal bias network shown in Figure 7-1 creates a mismatch in input bias currents (see Figure 5-7, Figure 5-8, and Figure 5-9) when a differential voltage is applied between the input pins. If additional external series filter resistors are added to the circuit, a mismatch is created in the voltage drop across the filter resistors. This voltage is a differential error voltage in the shunt resistor voltage. In addition to the absolute resistor value, mismatch resulting from resistor tolerance can significantly impact the error because this value is calculated based on the actual measured resistance.
The measurement error expected from the additional external filter resistors can be calculated using Equation 4, and the gain error factor is calculated using Equation 5.
The gain error factor, shown in Equation 4, can be calculated to determine the gain error introduced by the additional external series resistance. Equation 4 calculates the deviation of the shunt voltage, resulting from the attenuation and imbalance created by the added external filter resistance. Table 7-2 provides the gain error factor and gain error for several resistor values.
Where:
DEVICE (GAIN) | GAIN ERROR FACTOR | GAIN ERROR (%) |
---|---|---|
A1 devices (20) | 0.99658 | –0.34185 |
A2 devices (50) | 0.99598 | –0.40141 |
A3 devices (100) | 0.99598 | –0.40141 |
A4 devices (200) | 0.99499 | –0.50051 |
A5 devices (500) | 0.99203 | –0.79663 |
The INA281-Q1 is a unidirectional, current-sense amplifier capable of measuring currents through a resistive shunt with shunt common-mode voltages from –4 V to +110 V.
In this example application, the common-mode voltage ranges from 0 V to 24 V. The maximum sense current is 1.5 A, and a 5-V supply is available for the INA281-Q1. Following the design guidelines from Section 7.1.1, a RSENSE of 50 mΩ and a gain of 50 V/V are selected to provide good output dynamic range. Table 7-3 lists the design setup for this application.
DESIGN PARAMETERS | EXAMPLE VALUE |
---|---|
Power supply voltage | 5 V |
Common mode voltage range | 0 V to 24 V |
Maximum sense current | 1.5 A |
RSENSE resistor | 50 mΩ |
Gain option | 50 V/V |
The INA281-Q1 is designed to measure current in a typical solenoid application. The INA281-Q1 measures current across the 50-mΩ shunt that is placed at the output of the half-bridge. The INA281-Q1 measures the differential voltage across the shunt resistor, and the signal is internally amplified with a gain of 50 V/V. The output of the INA281-Q1 is connected to the analog-to-digital converter (ADC) of an MCU to digitize the current measurements.
Solenoid loads are highly inductive and are often prone to failure. Solenoids are often used for position control, precise fluid control, and fluid regulation. Measuring real-time current on the solenoid continuously can indicate premature failure of the solenoid which can lead to a faulty control loop in the system. Measuring high-side current also indicates if there are any ground faults on the solenoid or the FETs that can be damaged in an application. TheINA281-Q1, with high bandwidth and slew rate, can be used to detect fast overcurrent conditions to prevent the solenoid damage from short-to-ground faults.
The INA281-Q1 is a unidirectional current-sense amplifier that is meant to operate with a positive differential input voltage (VSENSE). If negative VSENSE is applied, the device is placed in an overload condition and requires time to recover once VSENSE returns positive. The required overload recovery time increases with more negative VSENSE.
Figure 7-3 shows the output response of a solenoid.
The INA281-Q1 power supply can be 5 V, whereas the input common-mode voltage can vary between –4 V to 110 V. The output voltage range of the OUT pin, however, is limited by the voltage on the power-supply pin.
Attention to good layout practices is always recommended.
For related documentation see the following: Texas Instruments, INA281EVM user's guide
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This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with appropriate precautions. Failure to observe proper handling and installation procedures can cause damage. | |
ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more susceptible to damage because very small parametric changes could cause the device not to meet its published specifications. |
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