Allegro MicroSystems, Inc. Site Map • Contact Us
中文 • English

High-Performance Power ICs and Hall-Effect Sensors

ACS750 Current Sensor Frequently Asked Questions ....

What are the differences between the –100, –075, and –050 versions of the ACS750?

The ACS750xCA-075 and the ACS750xCA-100 are physically the same part, but they are tested using different test programs. The sensitivity of both devices is ~20 mV per ampere. Both devices share the same specifications at 25ºC, but certain parameters, such as linearity and accuracy, are itemized to particular temperature ranges on the data sheet. For example, the operating temperature range of the ACS750ECA-100 is de-rated to allow performance through 100 A, and the specifications of the ACS750LCA-075 are guaranteed through the full automotive temperature range of -40ºC to 150ºC.

The only difference between those two versions and the –050 version of the device is the sensitivity. For the –050 version, sensitivity is set to ~40 mV per ampere.

Can the ACS750 family sense both dc and ac currents?

The ACS750 family uses Hall effect technology, which is capable of sensing electrical currents having both dc and ac components. As the data sheet states, the bandwidth of the ACS750 is 13 kHz typical. There is usually a phase lag of at least 45º on the output for ac currents at frequencies exceeding 13 kHz. For transient current signals, the response time can be expected to be ~25 µs.

Can the ACS750 sense 0 to 200 A as well as ±100 A?

No, the maximum current in the sensing range of the ACS750 is an absolute current of 100 A. The magnetic circuit within the ACS750 package will not provide a linear output above field levels generated by 100 A.

What does "ratiometric" mean?

This feature is particularly valuable when using the ACS750 with an analog-to-digital converter. A/D converters typically derive their LSB from a reference voltage input. If the reference voltage varies, the LSB will vary proportionally. The ratiometric feature of the ACS750 means its gain and offsets are proportional to its supply voltage, VCC. If the reference voltage and the supply voltage for the ACS750 are derived from the same source, the ACS750 and the A/D converter will both track those variations, and such variations will not be a source of error in the analog-to-digital conversion of the ACS750’s output.

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 ACS750 package body.

Is there any way to adjust the gain of the ACS750?

No, the ACS750 sensitivity and 0-ampere quiescent voltage level are programmed at the factory.

How small of a current can the ACS750 resolve?

The ACS750 can resolve a change in current level as small as 0.3% of full scale, at 25ºC, through its primary conductor leads. At that level, the amount of magnetic field coupled into the linear Hall Effect IC is just above its noise floor. However, depending on the temperature, 0-ampere offset error, and the dc current level, the percentage error of the current sensor output will often be greater than this minimum resolvable current.

What determines the maximum accuracy tolerance of the ACS750?

The maximum accuracy tolerance given for the ACS750 is based the 6-sigma limit of its accuracy distribution. Competing devices frequently specify their accuracy only over less than their full measurement range of current, at restricted temperature, and with less than full-scale current excursions to define magnetic hysteresis. The histogram below illustrates a typical distribution of ACS750 accuracy. The data is taken from a random sample of parts from 14 different manufacturing lots.

ACS750 Accuracy Tolerance

Can I buy parts that have been screened from the central portion of this distribution?

No. If you require a device with tighter worst-case accuracy, use the ACS754 family. Datasheets may be found on the Allegro website at http://www.allegromicro.com/en/Products/Part_Numbers/0754/index.asp.

Can Allegro bend the leads under the package or outward, so that I can surface-mount the ACS750?

In order to safely conduct 100 A currents, the power leadframe in the ACS750 has been constructed with a relatively heavy gauge. Because of this heavy gauge, the terminal leads are not very flexible. If the ACS750 is surface-mounted, small amounts of board flex, or the action over time of thermal expansion and contraction, would break the IC off the board. Allegro does not believe surface-mounting is practical for this device.

How should I solder the ACS750 onto my board?

To ensure a robust joint to the board, Allegro recommends adding a ring of through-holes in the solder pad area around each of the two broad terminals that carry the current being sensed. These holes are shown in the diagram in the FAQ "Do you have a recommended footprint for the ACS750 (CA package)?". General soldering recommendations for CA package, which is used for the ACS750, have been added to the application note Soldering Methods for Allegro's Products, which is on the Allegro website at www.allegromicro.com/en/Products/Design/an/an26009.pdf. The application note Hall-Effect Devices: Gluing, Potting, Encapsulating, Lead Welding and Lead Forming at www.allegromicro.com/en/Products/Design/an/an277031.pdf contains signal lead welding recommendations and temperature guidelines.

Do you have a recommended footprint for the ACS750 (CA package)?

Yes, the following shows the recommended footprint.

ACS750 Solder Pad

Can I get the Gerber files for your evaluation board?

Yes, click the following link: http://www.allegromicro.com/en/Products/Design/0750/Allegro_CA_CB_EvalBoard.zip.

I can't use Gerber files; is any other format available?

Yes, an AutoCAD 2004 .DXF file can be downloaded from: http://www.allegromicro.com/en/Products/Design/0750/Allegro_CA_CB_EvalBoardDXF.zip.

The copper areas are defined as "regions" in these files.

Are there any other design guidelines for applying the ACS750?

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 ACS750 (CA package)?

Typical measured inductance versus test signal frequency are:

  • 40 nH at 10 kHz
  • 35 nH at 100 kHz
  • 33 nH at 200 kHz

What is the overcurrent handling capability of the ACS750?

Bench testing indicates the following typical, 1-second overcurrent tolerances for the CA package at a 1% duty cycle (1 second duration, repeated every 100 seconds)

  • 25°C at 800 A
  • 85°C at 600 A
  • 150°C at 425 A

Does the ACS750 contain lead?

No, the ACS750 family is lead-free. All leads are coated with 100% matte tin, and there is no lead inside the package.

What is the high-current leadframe made of?

The heavy gauge leadframe is made of oxygen-free copper.

How susceptible is the ACS750 to stray magnetic fields?

The ACS750 contains a ferrite core that acts not only as a concentrator of the flux lines generated by Iprimary, but also as a shield to protect the sensor from ambient common-mode fields (typical rejection of common mode fields is -32 dB). The results are detailed in the following chart, which compares the output voltages, Vout, of an unshielded linear Hall effect sensor with that of the ACS750. The devices have the same gain, and are exposed to the same magnetic field, applied in an air core through the top of the package.

ACS750 External Field Effects

What safety certifications does the ACS750 have?

The ACS750 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

What is the behavior of the ACS750 output during a slow ramp-up of VCC?

The typical output behavior of the ACS750xCA-050 during a 500 ms ramp-up of VCC is shown for both 0 A and 50 A in the following two charts:

Vcc ramp-up with 0 A input

Vcc ramp-up with 50 A input

How soon after the application of power will a valid signal be available from the ACS750?

The typical time to valid output is given in the following table and charts.

IP = 0 A

IP = 50 A

35 μs

65 μs

Startup of ACS750 with 0 amperes applied, then a VCC step from 0 to 5 V

Startup with 0 A input

Startup of ACS750 with 50 amperes applied, then a VCC step from 0 to 5 V

Startup with 50 A input

How will capacitive coupling between the current path in the ACS750 and the Hall plate effect the sensor output?

The typical capacitive coupling of a 20 V peak-to-peak signal on the current path is given in the following table.

Noise Frequency

Passed-Through Signal Magnitude

Attenuation

10 MHz

270 mV/20 V

–37.4 dB

5 MHz

65 mV/20 V

–49.8 dB

1 MHz

30 mv/20 V

–56.4 dB

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 ACS750?

Typical ESD tolerance is 6 kV human body model, 600 V machine model.

Copyright © 2008 Allegro MicroSystems, Inc. • 115 Northeast Cutoff, Worcester, MA 01606 USA • Phone: 1.508.853.5000 • Fax: 1.508.853.7895