FAQ - CZ37xx Series

CZ37xx

[Q0338]
・Is it possible to sense both DC current and AC current?
A.
・It is possible to sense both DC current and AC current.
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[Q0339]
・What is the difference between maximum primary current and linear sensing range?
A.
・Maximum primary current indicates the current value which can be applied for a long time in a current sensor and depends on the cross-sectional area of the primary conductor.
CZ-37xx can be damaged when they have been used for a long time over the maximum effective current value. If current flows at a short period within msec order, such as an over current, CZ-37xx is not damaged.
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[Q0340]
・How much current can be flown in CZ-37xx?
A.
・It is possible to flow current of up to 60Arms in CZ-37xx.
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[Q0341]
・Can CZ-37xx detect unipolar current? (ex. current detection of 0 to 21A)
A.
・CZ-37xx detects both bipolar and unipolar current.
Bipolar: CZ-370x series
Unipolar: CZ-372x series
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[Q0342]
・How small current can the CZ-37xx resolve?
A.
・The current resolution is determined by its output noise voltage.
The current resolution can be increased by applying a noise filtering circuit.
(a) 0.1μF bypass capacitor should be placed close to VDD and VSS pins of CZ-37xx.
(b) Add a low-pass filter if it is necessary. The C1 values should be fixed in consideration of load conditions.
Figure 1. External Circuit example
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[Q0343]
・How much is the temperature drift of the primary conductor resistance of CZ-370x?
A.
・The temperature drift of the primary conductor resistance of CZ-370x is shown in Figure 2.
Figure2. CZ-37xx Temperature Drift of the Primary Conductor Resistance (normalized at 25°C)
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[Q0344]
・What is the variation in primary conductor resistance?
A.
・The primary conductor resistance of CZ-37xx varies from 0.21 to 0.30mΩ (reference) at 25°C.
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[Q0345]
・What is the inductance of the primary conductor?
A.
・The Primary Conductor Inductance of CZ-37xx is about 3nH (reference) at 25°C.
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[Q0346]
・What does "ratiometric" mean?
A.
・The CZ-37xx has a ratiometric output. This means that the output of the current sensor changes proportionally to the supply power voltage. A ratiometric output is suitable for applications where the output is converted to digital using an A/D converter and where fluctuation of the power supply voltage causes reference error of the A/D converter.
The supply voltage of the CZ-37xx and the reference voltage of A/D converter fluctuate at the same ratio. This will avoid the effects of the fluctuation of the power supply to the A/D converter output.
Table 3 shows the VDD dependence of VREF voltage.
Figure 3 shows the output voltage of the CZ-3702 (Sensitivity Vh=100mV/A) as an example ratiometric output.
Table 3. VDD dependence of VREF voltage
Figure3. Output voltage of the CZ-3702 vs Input current with different VDD. (Top: VOUT, Down: VOUT-VREF)
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[Q0347]
・How soon after power-on will a valid signal be available from the CZ-37xx?
A.
・Figure 4 shows a recommended example of the power up sequence.
In the power up sequence, if the time from VDD=3.7V to VDD=5V is less than 0.4msec, the output will be stabilized after 1.2msec (typ.) from the time VDD=3.7V. If it takes 0.4msec or more, it may take longer to stabilize the output. Please check the time needed to stabilize the output in that case.
Figure4. Recommended example of the power up sequence
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[Q0348]
・What is the response time?
A.
・The response time of CZ-37xx is typically 1μs with a load capacitance of 1000pF.
Figure 5. shows the typical pulse response waveform.
Rise response waveform
Fall response waveform
Figure 5. Pulse response waveform of CZ-37xx
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[Q0349]
・What is the recovery time from a fully saturated output?
A.
・The recovery time is 2μs or less.
Figure 6. Response waveform of CZ-3700 (Saturation condition: IIN=15A → Not Saturation condition: IIN=0A)
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[Q0350]
・What happens if a load capacitance over 1000pF is inserted to the CZ-37xx VOUT?
A.
・CZ-37xx do not output the correct value because of the oscillation of output.
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[Q0351]
・What happens if a load current over +/-2mA is applied to CZ-37xx VOUT?
A.
・In this case the CZ-37xx does not output the correct value.
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[Q0352]
・Does CZ-37xx show magnetic hysteresis?
A.
・No, because CZ-37xx does not contain magnetic material.
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[Q0353]
・What safety standards CZ-37xx have?
A.
・CZ-37xx have been certified with IEC/UL-60950 and UL1577 by the international certification association.
◾ IEC/UL 60950-1 – Information Technology Equipment – Edition 2. (File No. E359197)
◾ CSA C22.2 NO. 60950-1-07 – Information Technology Equipment – Edition 2. (File No. E359197)
◾ UL1577-Optical Isolators-Edition 5.(File No. E499004)
◾ CSA Component Acceptance Service No. 5A-Component Acceptance Service for Optocouplers and Related Devices (File No. E499004)
Click here for details
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[Q0354]
・What is the clearance distance and the creepage distance?
A.
・The clearance distance and the creepage distance are both over 8.0mm.
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[Q0355]
・What is the CTI of the package?
A.
・The Comparative Tracking Index (CTI) of the CZ-37xx package resin is 600V. The Material Group is I.
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[Q0356]
・How much is the working voltage of CZ-37xx?
A.
・CZ-37xx can be used under the following conditions.
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[Q0357]
・Is it allowable to use this device over the rating isolation voltage of the data-sheet?
A.
・The device should be used within a recommended condition.
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[Q0358]
・What is the voltage noise rejection ratio?
A.
・The Voltage Noise Rejection Ratio of the Primary Conductor was calculated by measuring the output while a high frequency sine wave voltage was applied as the input noise to the primary conductor.
Table 4 shows the CZ-37xx series having a strong voltage noise rejection ratio.
Figure 7. shows the frequency dependency of the voltage noise rejection ratio.
Table 4. Voltage Noise Rejection Ratio when high frequency sine wave voltage (20Vpp) is applied
Figure 7. CZ-37xx Noise Frequency vs Voltage Noise Rejection Ratio
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[Q0359]
・What are the constant parameters of RC?
A.
・Please decide the parameters considering the requirement of output resolution and response time (Please refer to Question 5).
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[Q0360]
・How should I solder the CZ-37xx to the board?
A.
・Please refer to "Soldering condition" described in Important notices page.
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[Q0361]
・Is there the recommended land pattern?
A.
・Yes. The recommended land pattern is shown in Figure 8 & Table 5.
Figure 8. Recommended pad pattern
Table 5. Recommended pad dimensions
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[Q0362]
・Are there any other board layout guidelines of CZ-37xx?
A.
・Please see the application notes (2. Board Design Guidelines) here.
Click here for details
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[Q0363]
・Is gerber file of the evaluation board provided??
A.
・Yes, please download from: Gerber Files.
Click here for details
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[Q0364]
・What is the recommended circuit diagram to use the CZ-37xx?
A.
・In this subsection, we show three examples of the external circuit when using CZ37xx.
These are just examples and there are other possible circuits. Please evaluate your external circuit by yourself.

Case 1) Connecting a 5V A/D converter in the subsequent stage
(a) A 0.1μF bypass capacitor should be placed close to VDD and VSS pins of CZ-37xx.
(b) Add a low-pass filter to VOUT and VREF pins if it is necessary. The R1 and C1 values should be fixed in consideration of the time constant of the filter and load conditions.

Case 2) Connecting a 3V A/D converter in the subsequent stage
(a) 0.1μF bypass capacitor should be placed close to VDD and VSS pins of CZ-37xx.
(b) Add a low-pass filter to VOUT and VREF pins if it is necessary. The R1, R2 and C1 values should be fixed in consideration of the time constant and the resistive divider ratio.

Case 3) Connecting an amplifier to change the reference voltage

Please see the application notes (2.1. External Circuits Example).
Figure 9. External Circuit Example 1, Figure 10. External Circuit Example 2, Figure 11. External Circuit Example 3
Click here for details
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[Q0365]
・I'm worried about the heat generated when applying a large current.
A.
・The CZ-37xx is capable of 60Arms continuous current, even larger current in case of transitional.
When CZ-37xx is used under conditions compliant with UL61800-5-1, please ensure the case temperature (Tc) is kept lower than 130℃ from heating by the primary current.
Please refer to the Figure 12. for the position to measure Tc.

If the heat dissipation is not enough, using thermal vias may help.
These can increase heat dissipation without increasing the trace area by thermally connecting the primary conductors to an inner or outer thermal layer directly.
Figure 12. Position to measure package case temperature
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[Q0366]
・What is the ESD tolerance?
A.
・CZ-37xx have the ESD tolerance which is more than 2000V by human body model (HBM) and more than 200V by machine model (MM).
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[Q0367]
・How much does CQ-330x have influenced from the other current line?
A.
・There are two Hall elements inside CZ-37xx connected in a differential manner.
By detecting the difference of these two Hall elements’ outputs, CZ-37xx reduces the effects of stray magnetic fields as a built-in common-mode rejection function.
When the same magnetic field is applied to both Hall elements, this magnetic field is deemed to be the stray and is reduced from the output of CZ-37xx by the ratio of Stray Magnetic Field Reduction (Ebc: 0.01A/mT Typ.).

Example: When a stray magnetic field of 1mT is applied to the CZ-37xx, the output will have additional error of 0.01A=10mA equivalent.
CZ-3700: Sensitivity=400mV/A, Error=10mA → Output error=4mV
CZ-3706: Sensitivity=12mV/A, Error=10mA → Output error=0.12mV

On the other hand, when different magnetic fields are applied to each Hall element, this will appear as output error.
For example, a current carrying trace that runs close the CZ-37xx may cause this.
Figure 13. Examples of nearby current lines
Figure 14. Output Error by nearby current
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[Q0368]
・Is there a way to estimate the temperature of CZ-37xx?
A.
・The temperature of the lead frame and the sensor inside the package are almost the same, the best estimated temperature would be of the lead frame.
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[Q0369]
・What is the effect on the device characteristics with respect to temperature change?
A.
・The graphs below show the change in characteristics when the ambient temperature is changed from 25 to -40 ° C and 105 ° C.
Figure 15 shows temperature drift of sensitivity, Figure 16 shows temperature drift of zero-current output, and Figure 17 shows total accuracy.
All graphs show “Average” and “Average ±3σ” of the actual result in a certain lot.
Figure 15. Temperature Drift of Sensitivity, Figure 17. Temperature dependency of Total Accuracy
Figure 16. Temperature Drift of Zero-current Output
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[Q0370]
・What is the impact on output when the voltage or the current applied to the primary?
A.
・Figure 18. shows the dV/dt noise of CZ-37xx output voltage (VOUT -VREF), when 1kV is applied to the primary conductor at the rise time of 1μs.
The yellow line shows the input voltage waveform and the pink line shows the output voltage waveform.
The convergence time is as short as 2μs. It is easy to avoid this noise by adjusting the capture timing.

Figure 19. shows the output voltage (VOUT -VREF) of CZ-37xx, when a 25A pulse is applied to the primary conductor with a pulse width of 1μs.
The yellow line shows the input current waveform and the green line shows the output voltage waveform.
The convergence time is as short as 2μs. It is easy to avoid this noise by adjusting the capture timing.
Figure 18. dV/dt noise waveform
Figure 19. dI/dt noise waveform
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[Q0371]
・Are CZ-37xx halogen-free/RoHS?
A.
・CZ-37xx are halogen-free/RoHS.
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[Q0372]
・Are CZ-37xx Pb-free?
A.
・CZ-37xx are Pb-free.
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[Q0373]
・What is the primary conductor made from?
A.
・The primary conductor is made from copper.
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[Q0374]
・What is the thermal resistance of the package?
A.
・The thermal resistance (θja) of CZ-37xx is 32°C/W when using the board shown in Figure 20.
Table 6. Thermal Resistance measurement board
Figure 20. Thermal Resistance measurement board
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[Q0375]
・Is it possible to use the internal EEPROM?
A.
・Sorry, internal EEPROM is not available.
Products will be shipped after the adjustment of EEPROM at factory test.
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[Q0376]
・Is it possible to order the customized products?
A.
・It is possible to customize depending on quantity conditions and requirement.
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[Q0377]
・Are there any precautions when using this product for the first time?
A.
・The Zero-Current Output of the CZ-37xx may drift over time within the values defined in datasheet Section 14.
Therefore, in order to minimize this drift, we recommend calibrating the Zero-Current Output by software after the power-up time of the system when the measured current is zero.
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[Q0378]
・Are there any precautions when using current sensors within the vacinity of stray magnetic fields/parts?
A.
・The CZ-37xx output can be affected by magnetic devices (mechanical relays, transformers, etc.) that are nearby.
In the case where magnetic devices must be placed close to the CZ-37xx, please check the effect on sensitivity or other characteristics and make sure any effects are understood and mitigated as much as possible.
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