ACS37220LEZATR-100B3 Current Sensor Compact Carrier -100A to +100A, 3.3V

Pololu is offering these breakout boards with support from Allegro Microsystems as an easy way to use or evaluate their ACS37220 Hall effect-based, electrically isolated current sensors with user-configurable overcurrent fault output; Pololu therefore recommend careful reading of the ACS37220 datasheet before using this product. The following list details some of the sensor’s key features:

• Hall effect-based sensor with electrically isolated current path allows the sensor to be inserted anywhere along the current path and to be used in applications that require electrical isolation.
• Extra-low primary current path resistance of 0.1 mO in the sensor IC for higher efficiency.
• Differential Hall sensing rejects common-mode fields, so the orientation of the sensor relative to uniform external magnetic fields (e.g. the Earth’s magnetic field) has less effect on the measurement.
• High-bandwidth 150 kHz analog output voltage proportional to AC or DC currents.
• Less than 4 µs response time.
• Output is not ratiometric (i.e. the zero point and sensitivity are independent of the actual supply voltage), which provides immunity from noisy supplies.
• User-configurable overcurrent fault output with 3 µs response time indicates when the current magnitude exceeds the set threshold and can be used for fast short-circuit detection.
• Integrated digital temperature compensation circuitry allows improved accuracy over the full operating temperature range.
• Automotive-grade operating temperature range of -40°C to 150°C.
• Carrier boards, available in compact and large sizes, offer a variety of ways to insert it into the current path along with 0.1"-pitch (breadboard-compatible) power, ground, and output pins.
• The PCB is made with 2-layer (compact versions) or 6-layer (large versions) 2-oz copper, so very little power is lost in the module.
• 3.3V and 5V versions available.

The connection points are labeled on the silkscreen, which is on the bottom side of the compact versions and on both sides of the large versions. The bottom silkscreen also shows the direction that is interpreted as positive current flow via the +i arrow.

The following table lists the available ACS37220 carrier options:

Details for item #5290

ACS37220LEZATR-100B3 Current Sensor Compact Carrier -100A to +100A, 3.3V, bottom view.

ACS37220 Current Sensor Compact Carrier.

This compact carrier features the ACS37220LEZATR-100B3, which is intended for nominal 3.3 V operation and is designed for bidirectional input current from -100 A to +100 A. This version can be visually distinguished from the other versions by the “3V3 B10” printed on the bottom side, as shown in the left picture above.

Using the sensor

This sensor has five required connections: the input current (IP+ and IP-), logic power (VDD and GND), and the sensor output (VOUT).

The sensor requires a supply voltage of 3.15 V to 3.45 V to be connected across the VDD and GND pads, which are labeled on the bottom silkscreen. The sensor outputs an analog voltage on VOUT that is centered at 1.65 V and changes by 13.2 mV per amp of input current, with positive current increasing the output voltage and negative current decreasing the output voltage:

VOUT=1.65V+0.0132VA·IP

IP=VOUT–1.65V0.0132VA=(VOUT–1.65V)·75.8AV

The output is not ratiometric, so the zero point and sensitivity are independent of the actual supply voltage.

Setting the overcurrent fault threshold

The optional VOC pin can be used to set the overcurrent fault threshold. An on-board 130 kO resistor between VOC and GND sets the default overcurrent fault threshold to approximately 200% of the nominal sensing range, and an external resistor can be added in parallel between VOC and GND to lower this threshold to between 50% and 200%. The following equation gives the value of this parallel resistor, R_OC, in kO as a function of overcurrent fault threshold percentage P:

ROC=130kO·P197%–P

So for example, to set the overcurrent fault limit to 50% of the nominal sensing range, a 44 kO external resistor can be added between VOC and GND:

ROC=130kO·50%197%–50%˜44kO

As a shortcut, VOC can be connected directly to ground to set the overcurrent fault limit to 100% of the nominal sensing range.

Alternatively, the on-board resistor can be replaced, or a low-impedance voltage source can be applied directly to the VOC pin as described in the ACS37220 datasheet.

The optional FAULT pin is normally at VDD and is pulled low when the IP current magnitude exceeds the set overcurrent fault threshold in either direction. This pin only asserts while the fault condition is present (it is not latched).

Making connections to the board

You can insert the board into your current path in a variety of ways. For typical high-current applications, you can solder wires directly to the through-holes that best match your wires, or you can use solderless ring terminal connectors, as shown in the pictures below. The largest through-holes are big enough for 10 AWG wires or #6 or M3.5 screws, and the second-largest through-holes (and mounting holes) are sized for 14 AWG wires or #2 or M2 screws. Holes with 0.1", 3.5 mm, and 5 mm spacing are also available as shown in the diagram above for connecting male header pins or terminal blocks, but please note that these connection options will generally not be suitable for the kinds of high currents intended for this sensor.

Warning: This product is intended for use below 30 V. Working with higher voltages can be extremely dangerous and should only be attempted by qualified individuals with appropriate equipment and experience.

Schematic and dimension diagrams

ACS37220 Current Sensor Carrier schematic diagram.

The dimension diagram is available as a downloadable PDF (403k pdf).

Real-world power dissipation considerations

Depending on the version, the ACS37220 can measure up to ±200 A. However, the sensor chip can overheat at lower currents. In Pololu's tests, Pololu found that Pololu's ACS37220 carrier boards could conduct 60 A continuously while staying well below the thermal limit for the IC. Pololu's tests were conducted at approximately 25°C ambient temperature with no forced air flow.

The actual current you can pass through the sensor will depend on how well you can keep it cool. The carrier’s printed circuit board is designed to help with this by drawing heat out of the sensor chip. Solid connections to the current path pins (such as with thick soldered wires or large, tightly-secured lugs) can also help reduce heat build-up in the sensor and carrier board.

Warning: Exceeding temperature or current limits can cause permanent damage to the sensor. If you are measuring an average continuous current greater than 50 A, Pololu strongly recommend that you monitor the sensor’s temperature and look into additional cooling if necessary.

This product can get hot enough to burn you long before the chip overheats. Take care when handling this product and other components connected to it.

Comparison of the Pololu current sensor carriers

Pololu have a variety of current sensors available with different ranges, sensitivities, and features. The table below summarizes Pololu's selection of active and preferred options:

Dimensions

General specifications

Identifying markings

Notes:

1

Typical.

File downloads

• Dimension diagrams of the ACS37220 Current Sensor Carriers (403k pdf)

• 3D model of the ACS37220 Current Sensor Compact Carriers (4MB step)

• Drill guide for the ACS37220 Current Sensor Compact Carriers (19k dxf)

  This DXF drawing shows the locations of all of the board’s holes.

Recommended links

• ACS37220 datasheet

• Allegro product page for the ACS37220 Hall-based Current Sensor

  Allegro product page for the ACS37220, where you can find additional application notes and other resources.