Figure 2. Input (IP−) and output (FAULT_EN) signal waveforms
of ACS710 configuration shown in figure 1 with COC = 100 nF.
Can the ACS710 family sense both DC and AC currents?
Yes. The ACS710 family uses Hall-effect technology, which is capable of sensing electrical currents having both DC and AC components. As the datasheet states, the bandwidth of the ACS710 is 120 kHz typical. There may be phase lag and amplitude attenuation of the output for AC currents with frequency content greater than 120 kHz. For transient current signals, the response time is ≈ 4 µs.
What does "ratiometric" mean?
This feature is particularly valuable when using the ACS710 with an analog-to-digital converter. A-to-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 ACS710 means its gain and offsets are proportional to its supply voltage, VCC. If the reference voltage and the supply voltage for the ACS710 are derived from the same source, the ACS710 and the A-to-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 ACS710 output. Figure 3 is a plot of primary current, IP, vs output voltage, VOUT, of the ACS710-25C 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 30.8 mV/A nominal.
Figure 3. ACS710-25C output voltage versus primary sensed current, at various supply voltage levels.
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 practicable to the ACS710 package body. Use of other external components depends on the application; please refer to Typical Application section of the datasheet.
Is there any way to adjust the gain of the ACS710?
No, the ACS710 sensitivity and 0-ampere quiescent voltage level are programmed at the factory.
How small of a current can the ACS710 resolve?
The current resolution of the ACS710 family of sensor ICs is limited by the noise floor of the device output signal. For example, the ACS710-12C version can resolve a change in current level of about 163 mA, at 25°C, at full bandwidth. The ACS710-25C version can resolve approximately 213 mA. At these levels, the amount of magnetic field coupled into the linear Hall-effect IC is just above its noise floor. Resolution can be improved significantly by filtering the output of the ACS710 for applications requiring lower bandwidth. The noise level and device output current resolutions at various bandwidths, achievable through filtering, are given in table 1 for the ACS710-12C, and in table 2 for the ACS710-25C. Filtering was accomplished with a simple, first order RC filter consisting of the internal resistor RF(INT) (typical value 1.7 kΩ) and an external filter capacitor CF.
|
Table 1. ACS710-12C Noise Level and Current Resolution
versus Filtering Capacitance and Resulting Bandwidth |
|
CF
(nF) |
BW
(kHz) |
VRMS Noise
(µV) |
VP-P Noise
(µV) |
Current Resolution
(mA) |
|
0 |
120 |
1523 |
9138 |
163 |
|
1 |
94 |
1185 |
7110 |
127 |
|
2.2 |
43 |
1010 |
6060 |
108 |
|
4.7 |
20 |
874 |
5244 |
94 |
|
10 |
9 |
768 |
4608 |
82 |
|
22 |
4 |
724 |
4344 |
78 |
|
47 |
2 |
682 |
4092 |
73 |
|
Table 2. ACS710-25C Noise Level and Current Resolution
versus Filtering Capacitance and Bandwidth |
|
CF
(nF) |
BW
(kHz) |
VRMS Noise
(µV) |
VP-P Noise
(µV) |
Current Resolution
(mA) |
|
0 |
120 |
994 |
5964 |
213 |
|
1 |
94 |
948 |
5688 |
203 |
|
2.2 |
43 |
713 |
4278 |
153 |
|
4.7 |
20 |
658 |
3948 |
141 |
|
10 |
9 |
602 |
3612 |
129 |
|
22 |
4 |
570 |
3420 |
122 |
|
47 |
2 |
536 |
3216 |
115 |
What is the ESD tolerance of the ACS710?
Typical ESD tolerance is 6 kV Human Body Model, and 600 V Machine Model.
What is the inductance of the ACS710 current carrying conductor?
Typical values for measured inductance versus test signal frequency are:
- 3.1 nH at 10 kHz
- 2.8 nH at 100 kHz
- 2.5 nH at 200 kHz
What is the capacitance between the ACS710 current carrying conductor and sensor IC ground?
The capacitance between the ACS710 current carrying conductor and sensor ground is about 2 pF.
Does the ACS710 contain lead (Pb)?
No, the ACS710 family is lead (Pb) free. All pins are plated with 100% matte tin, and there is no lead inside the package.
Can I get the Gerber files for your evaluation board?
Yes, download from: ACS710 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: ACS710 Layout Drawing (PDF).
What are the creepage and clearance distances between the current path and the sensing circuit?
The clearance distance in an ACS710 application is typically equal to the distance between the solder pads on opposite sides of the sensor package. Based on the recommended solder pad layout in the datasheet, it measures approximately:
9.50 − 2 × ( 2.25 ⁄ 2 ) = 7.25 (mm)
The creepage distance on the surface of the sensor IC package measures approximately:
7.50 + 2.00 = 9.50 (mm)
The creepage distance on the surface of the printed circuit board on which the sensor IC is mounted may be increased, if necessary, by cutting a slit on the board between the solder pads on opposite sides of the sensor IC package. Refer to figure 4.
Figure 4. Typical slit cut into the PCB underneath the package,
separating the two banks of pins, to further control creepage.
How susceptible is the ACS710 to stray magnetic fields?
Assumptions:
A. The current carrying conductor is on the same plane as the Hall element, and
B. The conductor has an infinite length
The result based on above assumptions will be the worst case result in terms of the influence of the stray field generated by the current carrying conductor on the Hall element.
The magnetic field generated in the direction perpendicular to the plane in which the conductor and the Hall element lie, at the distance l to the conductor will be:
Β = µ × I ⁄ (2π × L) (tesla)
Where
µ = µ0 = 4π × 10-7(H/m) = 400π(nH/m), assuming no core material around,
I is in amperes, the current flowing in the conductor, and
L is in meters, the distance between the point under consideration and the conductor.
The analysis is based on the fact that the magnetic coupling coefficient of ACS710 family is typically 9.5 gauss per ampere (0.95 mT/A).
The graph in figure 5 shows absolute current error caused by a current carrying conductor which lies in the same plane as the Hall element, at various distances. The percentage error relative to full range and be calculated as:
Err = (absolute current error ⁄ IP) × 100 (%)
Figure 5. The absolute current error versus separation distance for various current values.
What safety certifications does the ACS710 have?
The ACS710 family has been certified by UL to the following standard:
UL1577 (Pending UL certificate)
The mold compound is UL recognized to UL94V-0.
What is the behavior of the ACS710 output during a slow ramp-up of VCC?
The typical output behavior of the ACS710-12C during a slow ramp-up of VCC is shown for 0 A in figure 6 and for 12.5 A in figure 7.
Figure 6. VCC ramp-up with IP = 0 A.
Figure 7. VCC ramp-up with IP = 12.5 A.
How soon after the application of power will a valid signal be available from the ACS710?
The typical time to valid output is given in table 3 and in figure 8 (IP = 0 A, VCC = 5 V) and figure 9 (IP = 12.5 A, VCC = 5 V). However, we recommend a 3X to 5X safety margin to account for power-on time variation over process and temperature ranges.
|
Table 3. ACS710-12C Input Current versus Power-On Time |
|
IP
(A) |
tPO
(µs) |
|
0 |
14 |
|
12.5 |
16 |
Figure 8. Startup of ACS710-12C with 0 A applied, then a VCC step from 0 to 5 V.
Figure 9. Startup of ACS710-12C with 12.5 A applied, then a VCC step from 0 to 5 V.
What is the response time of VIOUT from deep saturation?
The ACS710-25C VIOUT response time from deep saturation was measured at less than 9 µs. Please see the oscilloscope plot in figure 10 for details.
Figure 10. Test conditions: for saturation, VCC = 5 V, TA = 25°C,
IP = 180 A; for linear VIOUT, Ip = 40 A.
What is the frequency response of ACS710 current sensor IC?
The graph in figure 11 shows the results of a high level frequency response simulation of the ACS710 current sensor IC circuit. The plot on the top is the amplitude response and the plot on the bottom is the phase response.
Figure 11. Frequency response of the ACS710.
What happens if I try to drive more than the specified 10 nF maximum capacitance with the output of the sensor IC?
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 IC?
The ACS710 may not produce an valid output, because the output driver will not be able to supply sufficient current.
What is the overcurrent tolerance of the ACS710 devices?
The following overcurrent limit results are based on the Allegro ASEK710 evaluation board. The limits may be different on a different application board. For detailed information on the Allegro ASEK710 evaluation board, please see FAQ Can I get the Gerber files for your evaluation board?.
Table 4 presents results for continuous DC current, and table 5 presents results for pulsed current. Figure 12 shows the effects of various input current levels on die temperature.
|
Table 4. Continuous Current Overcurrent Limits
ASEK710 evaluation board, at various ambient temperatures |
|
tA
(°C) |
IP(OClim)
(A) |
|
25 |
45 |
|
85 |
35 |
|
125 |
25 |
|
Table 5. Pulsed Current Overcurrent Limits
ASEK710 evaluation board, at room temperature |
|
IP
(A) |
Duration
(ms) |
Duty Cycle
(%) |
Quantity of
Pulses Allowed |
|
100 |
3000 |
NA |
Single |
|
150 |
300 |
NA |
Single |
|
200 |
20 |
NA |
Single |
|
200 |
10 |
10 |
200 |
|
200 |
10 |
1 |
Unlimited |
Figure 12. ACS710 die temperature (°C) versus continuous DC IP current (A)
What does the characterization data look like at the sensor IC full linear sensing range, IR?
Please see the graphs in figure 13 for the distribution data from a group of ACS710-12C devices characterized for (13A) sensitivity, (13B) non-linearity, (13C) symmetry, and (13D) total error.
Figure 13A. ACS710-12C Sensitivity versus Ambient Temperature at IP = 37.5 A
Figure 13B. ACS710-12C Nonlinearity versus Ambient Temperature at IP = 37.5 A
Figure 13C. ACS710-12C Symmetry versus Ambient Temperature at IP = 37.5 A
Figure 13D. ACS710-12C Total Error versus Ambient Temperature at IP = 37.5 A
What is the overcurrent fault level error?
The graph in figure 14 shows the distribution of the OC fault level error over a range of operating ambient temperatures. The data is taken from a limited number of devices and is for reference only.
Figure 14. ACS710-25C Overcurrent Fault Error versus Ambient Temperature
How will capacitive coupling between the current path in the ACS710 and the Hall element affect the sensor IC output?
The leadframe noise rejection test is conducted by injecting a high-frequency sinusoidal frequency onto the high-current leads. The signal coupling onto the output of the Hall-effect device is then measured. The ACS710 family devices exhibit a high level of leadframe noise rejection as table 6 reveals. In addition, figure 15 indicates performance as a function of frequency.
|
Table 6. Typical Capacitive Coupling of
20 Vp-p Signal on the Sensed Current Path |
|
Frequency
(MHz) |
VOUT
(mVp-p) |
Noise Rejection
(dB) |
|
5 |
5 |
−72 |
|
10 |
16 |
−62 |
|
15 |
40 |
−54 |
|
20 |
58 |
−51 |
Figure 15. ACS710 noise rejection versus noise frequency