SBOS470B December 2019 – August 2022 INA293

PRODUCTION DATA

- 1 Features
- 2 Applications
- 3 Description
- 4 Revision History
- 5 Pin Configuration and Functions
- 6 Specifications
- 7 Detailed Description
- 8 Application and Implementation
- 9 Device and Documentation Support
- 10Mechanical, Packaging, and Orderable Information

- DBV|5

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:

Equation 1.

where:

- PD
_{MAX}is the maximum allowable power dissipation in R_{SENSE}. - I
_{MAX}is the maximum current that will flow through R_{SENSE}.

An additional limitation on the size of the current-sense resistor and device gain is due to the power-supply voltage, V_{S}, 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 R_{SENSE} and GAIN to keep the device from exceeding the positive swing limitation.

Equation 2.

where:

- I
_{MAX}is the maximum current that will flow through R_{SENSE}. - GAIN is the gain of the current-sense amplifier.
- V
_{SP}is the positive output swing as specified in the data sheet.

To avoid positive output swing limitations when selecting the value of R_{SENSE}, 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 in order 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.

Equation 3.

where:

- I
_{MIN}is the minimum current that will flow through R_{SENSE}. - GAIN is the gain of the current-sense amplifier.
- V
_{SN}is the negative output swing of the device.

Table 8-1 shows an example of the different results obtained from using five different gain versions of the INA293. 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 V_{S} = 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 | |

V_{DIFF} | Ideal differential input voltage | V_{DIFF} = V_{OUT} / G | 250 mV | 100 mV | 50 mV | 25 mV | 10 mV |

R_{SENSE} | Current sense resistor value | R_{SENSE} = V_{DIFF} / I_{MAX} | 25 mΩ | 10 mΩ | 5 mΩ | 2.5 mΩ | 1 mΩ |

P_{SENSE} | Current-sense resistor power dissipation | R_{SENSE} × I_{MAX}2 | 2.5 W | 1 W | 0.5W | 0.25 W | 0.1 W |

(1) Design example with 10-A full-scale current with maximum output voltage set to 5 V.