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https://www.digikey.ca/en/products/detail/yageo/RC0603FR-07100KL/726889
Output Inductor
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Choose standard value 150uH inductor:
https://www.digikey.ca/en/products/detail/würth-elektronik/7447709151/1994053
Note: the datasheet recommends using an inductor with a saturation current >4.5A to be well above the current limit of the buck converter. However, an inductor with the required inductance and high enough saturation current would be quite expensive. The converter supports 2.5A output, but since the load for this application is only ~500mA, the saturation current of 2.7A on the selected inductor should be sufficient.
Output Capacitor
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Setting the output ripple voltage to 50mV, C > 1.67 uF
The selected capacitor is 10uF rated for 35V. The voltage rating is kept 2-3x higher than the 12V that will be applied. The DC bias characteristics show that the capacitance remains above the required 1.67uF when 12V is applied.
https://www.digikey.ca/en/products/detail/murata-electronics/GRM21BR6YA106KE43K/8323870
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Previous Research
Implementation Ideas
“High” voltage & current passthrough should be done with an XT90 connector.
Current measuring can be implemented with a smaller current transformer to be mounted on the PCB
A simple ADC integrated (presumably 2 channel ADC) and possibly voltage divider circuit can be used to measure both current and voltage
This ADC should support I2C and SPI and may be fitted with a signal buffer IC
Fairly standard to be able to find an ADC that can operate at 3.3V
A single “low voltage connector” should be used
This would be some relatively fine pitch connector
Some standard molex thing
Four conductors on this connector
GND (this will be signal ground, but should be presumed as the same potential and non-isolated from the “high voltage passthrough gnd”
5V or 12 V input power (possibly a range that supports each of these and maybe more)
I2C or UART data lines (2 conductors for each of these protocols.
Alternatively, use the 12V and 5V stepped down from the input line to power all board ICs instead of plugging in external power
Powering the ADC
The ADC and buffer (if a buffer is included, just an idea) will ideally consume very miniscule current, on the order of less than 200mA which makes a simple LDO (low dropout regulator) viable
This LDO will take the low voltage input power and use that to power the ADC chip.
LDO has lower efficiency than a buck, but will save board space and will be more convenient to implment.
Because of the negligible total power requirements for the board a low efficiency doesnt matter as much
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Voltage fed through XT90 connector
Hall effect sensor measures the current passing through and outputs an analog voltage signal
Analog voltage signal is converted into digital signal.
Digital signal fed into MCU or application specific IC to be transmitted onto an I2C/SPI/UART bus
Input voltage broken down into 12V and 5V filtered clean rails
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Hall Effect Sensor
Operation: Outputs an analog signal upon detection of a magnetic field generated by flow of electrons (current). A greater current flow means a stronger magnetic field and higher flux density. Current flow through the hall effect VCC and ground pins. The introduction of an external magnetic field will influence the magnetic field of the moving current. The electrons deflected to one side which creates a charge imbalance which results in a potential difference across the sensor (Hall voltage). The level at which the electrons are deflected will allow for an analog output regarding the strength of the magnetic field. There are amplifiers within the sensor to amplify the input signals.
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