Hi all,
For my design with LDC3114-Q1, I previously used a 1.8V LDO (MIC5365-1.8YMT-TZ) which provided a constant 1.8V for the operation of LDC, which is well within the specified range (1.71 to 1.89V). In order to save some cost and space, I replaced it with a Zener diode configuration with a current limiting resistor, which resembled the one in the image. A 100nF capacitor is placed close to the LDC, which is not shown in this image.
I am measuring 4 coils with approximately 0.9 ms measurement time per coil, with a customer scan cycle, with no high current drive for any of the coil (RPn = 1). Nevertheless, as a safety setting, I limited the current to 3.3mA (VDDD = 3.3V). I am retrieving the RAW_DATA from the LDC and performing additional calculations using a µC. With the Zener diode config, the LDC was working fine, even at extreme temperatures (80°C and -40°C), and I was able to obtain good values from the LDC. However, I tested this only on one setup and when I measured the voltage supplied to the LDC using an oscilloscope, it kind of worried me. The behaviour can be seen in the image below.
The DC average that is provided to the LDC steeps to 1.65V, which is below the minimum recommended voltage (1.71V). Moreover, the voltage climbs up during the interval between the scan cycles, up to 2.2V (maximum allowed voltage on supply pins). I can understand that the Zener is not perfect voltage regulator, but for a low-power solution like LDC, it should still work, right? But I am not sure about its long-term effects.
I tried increasing the current limit (4.4mA), which made the DC average to go around 1.88V but the peak was already around 2.4V. Though both these configurations are working fine in extreme temperatures, I am speaking about the test on one IC, tested for a few minutes. Hence, I would like to know what will be the recommendation for the power supply. Will the Zener diode solution still good or should I, for sure, use a separate LDO.?
Thanks!!
