Description
This board is a simple carrier of Broadcom’s bidirectional ±10A ACHS-7121 Hall effect-based linear current sensor, which offers a low-resistance (~0.7 mΩ) current path and electrical isolation up to 3 kV RMS. This version accepts a bidirectional current input with a magnitude up to 10 A and outputs a proportional analog voltage (185 mV/A) centered at 2.5 V with a typical error of ±1.5%. It operates from 4.5 V to 5.5 V and is intended for use in 5 V systems.
Overview
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This current sensor is a carrier board or breakout board for Broadcom’s ACHS-7121/7122/7123/7124/7125 Hall effect-based linear current sensors; we therefore recommend careful reading of the ACHS-7121/7122/7123 datasheet (1MB pdf) or ACHS-7124/7125 datasheet (1MB pdf) before using this product. The following list details some of the sensor’s key features:
- The conductive path internal resistance is typically 0.7 mΩ, and the PCB is made with 2-oz copper, so very little power is lost in the board.
- Use of a Hall effect sensor means the IC is able to electrically isolate the current path from the sensor’s electronics (up to 3 kV RMS), which allows the sensor to be inserted anywhere along the current path and to be used in applications that require electrical isolation.
- 80 kHz bandwidth that can optionally be decreased by adding a capacitor across the board pins marked “filter”.
- High accuracy and reliability: typical total output error of ±1.5% at room temperature with factory calibration, an extremely stable output offset voltage, and almost zero magnetic hysteresis.
- Robust sensor IC can tolerate 100 ms transient current spikes up to 100 A.
- Wide operating temperature range of -40°C to 110°C.
The pads are labeled on the bottom silkscreen, as shown in the picture to the right. The silkscreen also shows the direction that is interpreted as positive current flow via the +i arrow.
We sell five different versions of this board (±10A, ±20A, ±30A, ±40A, and ±50A) so you should consider adding your own distinguishing marks or labels if you will be working simultaneously with multiple versions. A white box is provided on the bottom silkscreen of the board to make labeling easier. You can also distinguish the versions by reading the text on the IC.
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The ACHS-7121 sensor operates at 5 V and is designed for bidirectional input current from -10 A to 10 A. When Vcc is 5 V, the output voltage is centered at 2.5 V and changes by 185 mV per amp of input current, with positive current increasing the output voltage and negative current decreasing the output voltage. The ACHS-7121 current sensor works as a drop-in replacement for our older Allegro ±5A ACS714 current sensor in many applications.
This board ships assembled with all surface mount components, and a 3×1 strip of 0.1″ header pins is included but not soldered in.
Using the sensor
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This sensor has five required connections: the input current (IP+ and IP-), logic power (VCC and GND), and the sensor output (OUT).
The sensor requires a supply voltage of 4.5 V to 5.5 V to be connected across the VCC and GND pads, which are labeled on the bottom silkscreen, and the sensor outputs an analog voltage that is linearly proportional to the input current.
The FILTER pin lets you adjust the board’s bandwidth by adding a capacitor, CF, to ground (a ground pad has been added next to the FILTER pin for convenience) in parallel with the 1 nF capacitor that is already on the board. Without any external filter capacitor, the bandwidth is 80 kHz. The datasheet provides more information on how the external filter capacitor affects bandwidth.
You can insert the board into your current path in a variety of ways. For low-current applications, you can solder 0.1″ male header pins to the board via the smallest pair of through-holes on the input-current side of the board. For higher-current applications, you can solder wires directly to the through-holes that best match your wires, or you can use solderless ring terminal connectors. The largest pair of through-holes are big enough for #6 screws.
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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 protective gear.
Schematic and dimension diagrams
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Schematic diagram of the ACHS-712x Current Sensor Carrier. |
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The dimension diagram is available as a downloadable PDF (318k pdf).
Specifications
| Parameter | Value |
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| Size | 0.7" x 0.8" |
| Weight | 1.1 g |
| Current sense | 0.185 V/A |
| Minimum logic voltage | 4.5 V |
| Maximum logic voltage | 5.5 V |
| Supply current | 15 mA |
| Version | -10A to +10A |
| PCB dev codes | cs01a |
| Other PCB markings | 0J1214, blank white box |
Resources
- Broadcom ACHS-7121, 7122, and 7123 current sensor datasheet
- Broadcom ACHS-7124 and 7125 current sensor datasheet
- Dimension diagram of the ACHS-712x Current Sensor Carriers
- 3D model of the ACHS-712x Current Sensor Carriers
- Drill guide for ACHS-712x Current Sensor Carriers
- New products: ACHS-7124/7125 current sensor carriers
- New products: ACHS-7121/7122/7123 current sensor carriers
