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ACS706 Current Sensor Frequently Asked Questions 
- Can the ACS706 family sense both dc and ac currents?
- What does "ratiometric" mean?
- What external components are required?
- Is there any way to adjust the gain of the ACS706?
- How small of a current can the ACS706 resolve?
- Can I get the Gerber files for your evaluation board?
- I can't use Gerber files; is any other layout data available?
- How thick are the copper traces on your evaluation board?
- Are there any other design guidelines for applying the ACS706?
- What is the inductance of the ACS706?
- Does the ACS706 contain lead?
- What is the composition of the leadframe?
- How susceptible is the ACS706 to stray magnetic fields?
- What safety certifications does the ACS706 have?
- What happens if I try to drive more than the specified 10 nF maximum capacitance with the output of the sensor?
- What happens if I try to drive less than the specified 4.7 kΩ minimum resistance with the output of the sensor?
- What is the ESD tolerance of the ACS706?
- What is the overcurrent tolerance of the ACS706?
Can the ACS706 family sense both dc and ac currents?
The ACS706 family uses Hall effect technology, which is capable of sensing electrical currents having both dc and ac components. The bandwidths of the ACS706ELC-20A and –05C are 50 kHz typical. There is usually a phase lag of at least 45º on the output for ac currents at frequencies exceeding these values.
The ratiometric feature of the ACS706 means its gain and offsets are proportional to its supply voltage, VCC. This feature is particularly valuable when using the ACS706 with an analog-to-digital converter. A-to-D converters typically derive their LSB from a reference voltage input. If the reference voltage varies, then the LSB varies proportionally. If the reference voltage and the supply voltage for the ACS706 are derived from the same source, then both the ACS706 and the A-to-D converter track those variations, and such variations will not be a source of error in the analog-to-digital conversion of the ACS706’s output. Below is a plot of primary current, IP, to output voltage, VOUT, of the ACS706ELC-20A when varying VCC. The offset and sensitivity levels shift proportionally with VCC. For example, when VCC = 5.5 V, the 0 A output is 5.5 / 2 = 2.75 V nominal, and the sensitivity is 110 mV/A nominal.
What external components are required?
Allegro recommends the use of a 0.1 µF bypass capacitor between the VCC pin and the GND pin. The capacitor should be located as close as practical to the ACS706 package body.
Is there any way to adjust the gain of the ACS706?
No, the ACS706’s mV/A sensitivity and 0-ampere quiescent voltage level are programmed at the factory.
How small of a current can the ACS706 resolve?
The filtering characteristics are provided in the following table:
ACS706ELC-20A Noise Filtering versus Frequency Response
| Break Frequency of R-C Filter on Output (kHz) |
Nominal Programmed Sensitivity (mV/A) |
Peak-to-Peak Noise (mV) |
Current Resolution (mA) |
Measured Rise Time for 5 A Step, Filtered (µs) |
Bandwidth as Derived from Step Response (kHz) |
|---|---|---|---|---|---|
| Unfiltered | 100 | 75 | ≈750 | 9 | 50 |
| 50 | 46 | ≈460 | 10.5 | 33.3 | |
| 40 | 43 | ≈430 | 12 | 30 | |
| 10 | 25 | ≈250 | 35 | 10 | |
| 7.0 | 17 | ≈170 | 70 | 5 | |
| 3.3 | 12 | ≈120 | 101 | 3.3 |
Can I get the Gerber files for your evaluation board?
Yes, download from:
http://www.allegromicro.com/en/Products/Part_Numbers/0706/ACS700-RevC-Gerber
Files.zip.
I can't use Gerber files; is any other layout data available?
Yes, a layout drawing .PDF file can be downloaded from:
http://www.allegromicro.com/en/Products/Part_Numbers/0706/ACS700-PWB-Rev_C_Fabrication_Drawing.pdf.
How thick are the copper traces on your evaluation board?
The evaluation board uses 2-oz. copper.
Are there any other design guidelines for applying the ACS706?
Care should be taken to minimize the inductance of the current path to be measured. Also, attention should be paid to minimizing the contact/connection resistance of any connections in that path.
What is the inductance of the ACS706?
Typical measured inductance versus test signal frequency:
- 6.5 nH at 10 kHz
- 6.5 nH at 100 kHz
- 6.7 nH at 200 kHz
The lead frame of the ACS706 is plated with lead-free, 100% matte tin and hence should be processed and soldered accordingly. However the ACS706 is a flip-chip device, and the solder balls inside the package that connect the die to the leadframe are 95% lead, 5% tin. Lead-free alternatives for high-temperature flip-chip solder balls are not yet commercially available, and therefore solder balls of this composition are exempted from lead-free requirements by the WEEE (Directive 2002/96/EC of the European Parliament and of the Council of 27 January 2003 on Waste Electrical and Electronic Equipment) and RoHS (Directive 2002/95/EC of the European Parliament and of the Council of 27 January 2003 on the Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment).
What is the composition of the leadframe?
The leadframe is made of oxygen-free copper.
How susceptible is the ACS706 to stray magnetic fields?
Because the ACS706 does not employ a magnetic concentrator, it is more susceptible to external magnetic fields than our ACS75x sensor families. The susceptibility of the ACS706 to external fields can be mitigated via proper orientation, spacing from external field sources, and if necessary, shielding of the sensor. An application note, Managing External Magnetic Field Interference When Using the ACS70x addresses mitigation techniques in greater detail. It can be downloaded from: http://www.allegromicro.com/en/Products/Design/an/an26030.pdf.
What safety certifications does the ACS706 have?
The ACS706 family also has been certified by TÜV America to the following standards:
- UL 60950-1:2003
- EN 60950-1:2001
- CAN/CSA C22.2 No. 60950-1:2003
The mold compound is UL recognized to UL94V-0.
What happens if I try to drive more than the specified 10 nF maximum capacitance with the output of the sensor?
The output of the sensor may oscillate.
What happens if I try to drive less than the specified 4.7 kΩ minimum resistance with the output of the sensor?
The sensor may not produce an output, as its output driver will not be able to supply sufficient current.
What is the ESD tolerance of the ACS706?
Typical ESD tolerance is 5.5 kV human body model, 500 V machine model.
What is the overcurrent tolerance of the ACS706?
Because of its low, 1.5 mΩ internal resistance, the overcurrent capability of the ACS706 sensor is highly dependent on the characteristics of the circuit board on which it is mounted, including: trace width and thickness, the number of layers, and the presence or absence of ground and/or power planes. It is also dependent on the maximum operating temperature of your application and the frequency with which the overcurrent occurs.
By way of example, we have characterized ACS706 devices mounted on the Allegro ACS706 evaluation board. This a 2-layer board, with 2-oz. copper. (For drawings and Gerber files, see the FAQs: Can I get the Gerber files for your evaluation board? and I can't use Gerber files; is any other layout data available? on this page.) The results are provided in the following table.
| Tested Maximum ACS706 Overcurrent Levels and Durations Applicable to devices on Allegro ASEK 706 evaluation boards connected with 2 AWG cables |
|
|---|---|
| Ambient Temperature (°C) |
Maximum Current (A) |
| 10 s, 10% Duty Cycle, 100 pulses applied | |
| 25 | 40 |
| 85 | 30 |
| 3 s, 3% Duty Cycle, 100 pulses applied | |
| 25 | 50 |
| 85 | 40 |
| 1 s, 1% Duty Cycle, 100 pulses applied | |
| 25 | 60 |
| 85 | 50 |
| 250 ms, 0.25% Duty Cycle, 100 pulses applied | |
| 25 | 80 |
| 85 | 60 |
| 100 ms, 0.1% Duty Cycle, 100 pulses applied | |
| 25 | 100 |
| 85 | 80 |