POWER
Figure 2: Demonstration board overview of the ZXCT21x.
output voltage is the same as the supply voltage. To minimise noise, ensure that you grounding. Here, grounding is crucial for accurate measurements, therefore, use a common ground plane and connect the ground (GND) pin to a low-impedance ground. In general, the ZXCT21x does not need calibration as it is a high-precision device with only 100μV offset voltage and maximum gain error of 0.8 percent. The ZXCT21x has a zero-drift core to offer only 0.5μV/°C input offset drift across the full operating temperature range from -40°C to +125°C. Outside this temperature range, the accuracy may drift slightly so consider temperature compensation, if needed. However, regarding the system design, especially at high currents or wide temperature ranges, manual calibration can be performed in factory mode. By using an on-board microcontroller (MCU), calibrate the offset voltage and gain error as close to zero as possible for optimal accuracy. In addition, PCB layout considerations are critical for success. Keep the high-current traces away from sensitive analog circuitry, use proper bypassing and resistance and inductance. Based on your application’s requirements, there are also protection features to consider, such as reverse current protection, overcurrent protection and ESD protection. To support your next designs, Diodes Incorporated provides free evaluation boards and technical services, including application notes. The demonstration board, shown in Figure 2, includes one SOT363-packaged ZXCT21x, a decoupling capacitor at the power supply end and an interference suppression capacitor at the input end, two voltage divider
resistors for selecting VREF, one selector for connecting different voltages to the VREF terminal and six test point connectors (R3 and R4 omitted).
Figure 3: Recommended application circuit where the ADC’s in-pin is connected to the MCU’s ground pin.
Figure 4: ZXCT21x application circuit diagram used less often.
In common applications, the circuit shown in Figure 3 is often used. Here, the ADC’s in-pin is connected to the MCU’s ground pin. This circuit has the advantage that the ADC input voltage is always equal to (V1.0-V2.0) × gain, regardless
of how the VREF pin is connected. This means that only one measurement is needed to obtain the desired data, which reduces the workload of the ADC and MCU and improves
In contrast, the circuit shown in Figure 4 requires the measured data to be subtracted
from VREF, and this VREF value must either be set in advance or measured separately. This increases the workload of the MCU. Typically, the power supply voltage for the ZXCT21X is set to 5V or 3.3V, and the input voltage range of the ADC is 0V~5V or 0V~3.3V, respectively. Since the ADC and MCU must have compatible voltage levels, it may be necessary to use a level-shifter circuit to convert the signals between the two devices if they operate at different voltages. If there is interference, interference signals and improve stability. To measure bi-directional symmetric
current, set the VREF voltage to half of the supply voltage. For uni-directional positive
current, set the VREF voltage to 0.5V (or 0.2V, etc.). This will give the output voltage a range of 0.5V to 4.5V (or 0.2V to 4.8V). At zero current,
the output voltage will be equal to VREF. At maximum current, the output voltage will
be at its highest value, which increases the dynamic range of the output voltage. Similarly, to measure uni-directional negative
current, set the VREF voltage to 4.5V (or 4.8V, etc.), which will give the output voltage a range of 0.5V to 4.5V (or 0.2V to 4.8V). At maximum current, the output voltage will be
equal to VREF. At minimum current, the output voltage will be at its lowest value, which also increases the dynamic range of the output voltage.
In conclusion, the ZXCT21x series presents a compelling solution for current sensing needs in a variety of applications, particularly in the realms of industrial power supply (12V/24V) and USB PD 3.0 Standard (5/9/15/20V) for devices such as laptops, docking stations and portable chargers. The series addresses common challenges associated with current sensing, offering a streamlined alternative to the complex and less accurate discrete component solutions.
While discrete components may initially seem cost-effective, the additional design complexity, calibration efforts and potential performance compromises can ultimately lead to higher overall costs and inferior system performance.
DECEMBER/JANUARY 2025 | ELECTRONICS FOR ENGINEERS
35
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54
