2.5.2 Current Sensor

Summary Description


The NEXSYS Current Sensor (CS1) is a Series A (4 Pin) solid-state, low-side direct current (DC) sensor developed to enhance avionics design flexibility by offering undercurrent and overcurrent detection. The CS1 compares electric current in a linear relationship between the specified setpoint and the current that is being monitored by the SENSE input. The fast-response output provides a discrete signal that transitions from Open to Ground when the input detects current that is above or below the specified setpoint, see Figure

The NEXSYS Current Sensor features fault-tolerant circuitry and architecture that provides low-drift current sensing over temperature. The CS1 also offers an extensive range of setpoint options that afford design versatility; the choices range from 10 mA to 1000 mA (1.0 A).

The NEXSYS Current Sensor (CS1) is a commercial-off-the-shelf (COTS) item. This standard catalog hardware includes features to allow for flexible interface design solutions while also meeting aircraft performance standards. The CS is designed, tested, and qualified to MIL-PRF-22885/116, MIL-PRF-22885/117, DO-160 and MIL-STD-461 requirements. Specifications are available in our MIL-PRF and DO-160 Documents page, and the qualification table is available in Appendix A.

Input Characteristics

The NEXSYS Current Sensor inputs are Power (28V), Ground (GND) and Sense (SENSE). The inputs include the following characteristics for custom current sensing and output control. Current Sensor input circuity is diode isolated, buffered, and debounced for reliable operation. See additional sections for specific details concerning the Input/Output (I/O) interface.

28V (PIN 2): Operating Voltage (Nom.), Current Draw 2 mA (Max).
GND (PIN 4): Continuous Ground required, otherwise, inadvertent operation could occur.
SENSE (PIN 3): Detects DC input current and includes a hysteresis band to prevent signal chatter.

Output Characteristics

The NEXSYS Current Sensor features a conditioned Output Z (OUT Z) output that is open-drain High-Z (Open) when not active, and surge-protected against transients and overload conditions. The output load capacity is 0.5 A, see Figure (Operating Parameters) for electrical load rating types.

OUT Z (PIN 1): Active = Low (Ground), Not Active = High-Z (Open)

Configuration Options

The NEXSYS Current Sensor features an extensive range of setpoints to provide an Active Low (Ground) output when the specified undercurrent or overcurrent condition is detected, as detailed below. The Current Sensor can also be configured to perform wide hysteresis.



Overcurrent: Overcurrent: OUT Z (PIN 1) = Low (Ground), when current monitored by SENSE (PIN 3) is ABOVE the specified setpoint, see Figure

Undercurrent: OUT Z (PIN 1) = Low (Ground), when current monitored by SENSE (PIN 3) is BELOW the specified setpoint, see Figure

Wide Hysteresis: When combined with a NEXSYS Electronic Latch, the Current Sensor can perform wide hysteresis with different pull-in and drop-out levels for enhanced system noise tolerance.

Current Setpoints1: Two increment options that offer an extensive range of current setpoints in increments of 10 mA between 10 to 90 mA and in increments of 50 mA between 100 to 1000 mA.

10 mA Setpoints: 10, 20, 30, 40, 50, 60, 70, 80 and 90 mA.
50 mA Setpoints: 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 1000 mA.

1. The setpoint tolerance of SENSE (PIN 3) is +/- 5%. The unit has a hysteresis band (+/- 0.16%) that will prevent a state change until the sensed current exceeds hysteresis. Tolerance at EMC and Environmental extremes is +/- 10%. Current Sensor, Operating Parameters


Operating Parameters
Operating Voltage (Max./Nom./ Min.) +32 VDC /+28 VDC/+18 VDC
Power Supply Input Current 4 mA (Maximum)
Reset From Power Loss at 25°C 5 sec (Minimum) at +25°C
Hold Up On Power Loss at 25°C 50 ms (Minimum)
Input Parameters
Sense Current 10 mA to 1000 mA (1.0 A)
Setpoint Tolerance +/- 5%
Hysteresis Band +/- 0.16%
Typical TSENSE, Voltage Drop 50 mV to Ground
Transition Time Sense to Out (TSENSE) 10 ms (Maximum)
All Pulled-up inputs are diode isolated
Output Parameters
Output Load Capacity IntelliFET® 0.5 A (Resistive/Motor/Inductive/Lamp)
On-State Resistance at 25°C Typical 0.4 ohms / Maximum 0.6 ohms
Off-State Resistance at 25°C Open Drain (High-Z), Self-Protected IntelliFET®,
+32 VDC Maximum
Operating -55°C to +85°C
Non-operating -55°C to +125°C
MIL-HDBK-217F, Notice 2
Airborne Inhabited Cargo (AIC)
at +40°C Continuous Operation
MTBF = 422,347 hrs

For Qualification Summary, see Appendix A