12S Power Module
Status: Active
Owner: Zen, Taim
add link to A365 ?
Requirements
Passthrough 18 V - 55 V (6S lower voltage to 12S upper voltage )
Measure current through hall effect current sensing (without a shunt resistor to minimize losses)
Measures voltage with an ADC
I2C or UART interface
Preference toward I2C, but just pick one of them
XT90 connector for input power and output power
Maximum current passthrough requirements
Max pulsed current 200 A
Max continuous current 150 A
Steps down input voltage to clean 5V and 12V rails
Refer to Nathanās current power module, photos in discord, for a reference to what this board will be replacing.
Current Sensing
Ā | Hall Effect Sensor | INA228 IC |
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Description |
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Based on the above analysis, using an INA228 IC seems to be a better option for simpler implementation and integration. To minimize the losses with the shunt resistor, a resistance of 0.0005 ohms will be used (the current power module also uses this value). At max current of 75A, the resistor will dissipate 2.8W. To prevent overheating, a nonstandard resistor with a resistance of 0.0005 ohms and a power rating of 8W will be used, such as the one below.
https://www.digikey.ca/en/products/detail/koa-speer-electronics-inc/PSL2NTEBL500F/1039674
Block Diagram
The 12V output is left as a power pad so that a connector can be soldered onto it and a harness can be made as needed
The Molex connector is based on the connector standard for the Pixhawk, shown below
A 5V-3.3V LDO was added to provide a 3.3V rail for the SCL and SDA lines, as per the Pixhawk standard
5V Buck
Requirements
Steps down 18-55V to 5V
Current limit should be at least 5A
IC Selection
Ā | SIC462ED-T1-GE3 | TPS54560B | BD9G500EFJ-LAE2 |
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Voltage input range (V) | 4.5-60.0 | 4.5-60 | 7-76 |
Voltage output range (V) | 0.8-0.92xVin | 0.8-58.8 | 1-0.97*Vin |
Output current limit (A) | 6 | 5 | 5 |
Efficiency (%) | 94 | 91 | 82 |
Price ($) | 7.32 | 8.03 | 9.58 |
Link |
While the SIC462ED is the best option for price and efficiency, the beast of a chip has 30 pins. Based on simplicity and efficiency, the TPS54560B is chosen instead.
Typical Application Circuit
Pinout & Functions
Switching Frequency
Higher switching frequency allows for the use of smaller inductors and capacitors as well as lower output ripple, but it comes at the cost of increased switching losses
Since this application involves a relatively high voltage input, the selected switching frequency is 400kHz, which should provide a reasonably low ripple current while minimizing switching losses
Frequency Setting Resistor
For fsw= 400kHz, RT = 242K
Choose closest standard value, 243K
https://www.digikey.ca/en/products/detail/yageo/RC0603FR-07243KL/727084
Output Inductor
Vin_max = 55V, Vout = 5V, Iout= 5A, Kind = ĪIL/Iout = 0.3 (recommended by datasheet), and fsw= 400kHz
Using the equation above, Lmin = 7.6uH. Choose the next standard value of 8.2uH. The saturation current of the inductor should be greater than the switch current limit of 7.5A
OLD PART: https://www.digikey.ca/en/products/detail/wĆ¼rth-elektronik/7443330820/2175573
NEW PART: https://www.digikey.ca/en/products/detail/codaca/CSEB0770H-8R2M/16566340
Justification for new part: smaller size. (10.90mm x 10.00mm) vs (7.90mm x 7.60mm). New part has higher DCR and lower current rating.
Output Capacitor
Datasheet recommends Cout > 62.5uF to account for transient load response
Use 3x 47uF 10V caps to get Cout = 90uF at 5V DC bias, which is safely above the minimum 62.5uF
https://www.digikey.ca/en/products/detail/murata-electronics/GRM32EC81A476KE19L/2548451
Catch Diode
Reverse voltage rating must be > Vin_max = 55V
Current rating must be > max inductor current = 5.8A
Use schottky diode since it has lower forward voltage, resulting in higher converter efficiency
https://www.digikey.ca/en/products/detail/diodes-incorporated/PDS760-13/776756
Input Capacitor
As per datasheet, Cin > 3uF and should be X5R or X7R rated for at least Vin_max = 55V
Use 4x 2.2uF 100V, which provides 3.4uF at 55V DC bias
Samsung caps were chosen over Murata as the Murata option was 3x more expensive
https://www.digikey.ca/en/products/detail/samsung-electro-mechanics/CL32B225KCJZW6E/7320552
Bootstrap Capacitor
0.1uF 10V X5R capacitor is needed
https://www.digikey.ca/en/products/detail/murata-electronics/GCJ188R71E104KA12D/7363221
Undervoltage Lockout Setpoint Resistors
For the converter to start supplying when Vin > 6.5V and stop supplying when Vin < 5V, RUVLO1 = 441K and RUVLO2 = 90.9K
https://www.digikey.ca/en/products/detail/yageo/RC0603FR-07442KL/727243
https://www.digikey.ca/en/products/detail/yageo/RC0603FR-0790K9L/727424
Output Voltage & Feedback Resistors
For 5V output, RLS = 10.2K and RHS = 53.6K
https://www.digikey.ca/en/products/detail/yageo/RC0603FR-0710K2L/726883
https://www.digikey.ca/en/products/detail/yageo/AC0603FR-0753K6L/5896188
Compensation
=1768Hz
=707kHz
=35.35kHz
=18.8kHz
=16.08K
Use standard value 16K:
https://www.digikey.ca/en/products/detail/yageo/RC0603JR-0716KL/726721
=5626pF
Use standard value 5600pF:
https://www.digikey.ca/en/products/detail/murata-electronics/GRM1885C1H562JA01D/4421635
=49.7pF
Use standard value 51pF:
https://www.digikey.ca/en/products/detail/murata-electronics/GRM1885C2A510JA01D/586986
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3.3V LDO
Requirements
Steps down output from 5V buck to 3.3V to power the INA228, which draws 640uA of current
Selected IC
https://www.digikey.ca/en/products/detail/texas-instruments/TLV73333PDBVR/5022378
Steps down input of up to 5.5V to fixed 3.3V
Supplies up to 300mA of current
Typical Application Circuit
Capacitors
1uF X7R filtering capacitors on input and output
https://www.digikey.ca/en/products/detail/murata-electronics/GCM188R71C105MA64D/7430540
12V Buck
Requirements
Steps down 18-55V to 12V
The 12V rail is only used to power the vtx, which has a 500mA current draw. Ideally, the current limit of the buck converter should be closer to 750mA to be safe
IC Selection
Ā | LT8631IFE#PBF | LV2862XLVDDCR | LMR38020SDDAR |
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Voltage input range (V) | 3-100 | 4-60 | 3.8-80 |
Voltage output range (V) | 0.8-60 | 0.76-58 | 1-75 |
Output current limit (A) | 1 | 0.6 | 2 |
Efficiency @ 600mA load (%) | 81 | 92 | 90.5 |
Price ($) | 17.65 | 0.93 | 2.68 |
Link |
Based on price, current limit and efficiency, the LMR38020 is chosen.
Typical Application Circuit
Pinout & Functions
Switching Frequency
Higher switching frequency allows for the use of smaller inductors and capacitors as well as lower output ripple, but it comes at the cost of increased switching losses
Since this application involves a relatively high voltage input, the selected switching frequency is 400kHz, which should provide a reasonably low ripple current while minimizing switching losses
Frequency Setting Resistor
From the table in the datasheet, for a 400kHz switching frequency, R=64.9K
https://www.digikey.ca/en/products/detail/yageo/RC0603FR-0764K9L/727344
Adjustable Output Resistor
Vref is given as 1V and Vout is 12V. Choose RFBT to be 100K, then RFBB=9.09K
https://www.digikey.ca/en/products/detail/yageo/RC0603FR-079K09L/727418
https://www.digikey.ca/en/products/detail/yageo/RC0603FR-07100KL/726889
Output Inductor
Vin = 55V, Vout = 12V, fsw= 400kHz, Iout = 2A
K = ĪIL/Iout, choose k=0.4
Using the above equation, L = 29.3uH
Choose closest standard value, 33uH
Inductor saturation current should be >= Isc , the high side switch current limit of 3.2A, to avoid component damage due to high current when the inductor saturates
OLD PART: https://www.digikey.ca/en/products/detail/wĆ¼rth-elektronik/744770133/1638634
NEW PART: https://www.digikey.ca/en/products/detail/tdk-corporation/SPM10065VT-330M-D/12175283
Justification: Slightly smaller, cheaper, higher current and saturation current ratings.
Output Capacitor
Output capacitor allows for the load to be powered during the off state of the transistor and accounts for load transients
Voltage rating should be 2-3x the output voltage to account for voltage spikes
The datasheet recommends 22uF for a 12V output
Use 3x 22uF to account for DC bias at 12V
https://www.digikey.ca/en/products/detail/murata-electronics/GRM32ER71E226KE15K/13904980
Input Capacitor
At least 4.7uF X7R rated at twice the input voltage is required to reduce ripple and maintain input voltage during load transients
Option 1 ($4.29): https://www.digikey.ca/en/products/detail/murata-electronics/KCM55LR72A475KH01K/2785887
Option 2 ($2.67): use 3x 2.2uF 100V in parallel
https://www.digikey.ca/en/products/detail/yageo/CC1206KKX7R0BB225/5884563
100nF X7R rated at twice the input voltage is required for high frequency bypass
https://www.digikey.ca/en/products/detail/murata-electronics/GCJ21BR72A104KA01K/11618560
Bootstrap Capacitor
100nF 16V capacitor required to store energy for powering the mosfet gate drivers
https://www.digikey.ca/en/products/detail/murata-electronics/GCJ188R71E104KA12D/7363221
INA228 Current Sensing IC
Typical Application Circuit
Shunt Resistor
(Previous research based on 75A max current)
Resistance of 0.0005 ohms to minimize losses
At max current of 75A, the resistor will dissipate 2.8W. To prevent overheating, a nonstandard resistor with a resistance of 0.0005 ohms and a power rating of 8W is selected
https://www.digikey.ca/en/products/detail/koa-speer-electronics-inc/PSL2NTEBL500F/1039674
Given the high current requirement of 150A, consider using multiple shunt resistors in parallel to spread out the power dissipation across multiple resistors.
Ā | Single Shunt Resistor | Multiple Shunt Resistors in Parallel |
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The selected shunt resistor is 0.0002 ohms and rated for 15W. At max current, the power dissipated is 1502 * 0.0002 = 4.5W. The safety margin is over 3x, so it should be safe to use only a single shunt resistor.
https://www.digikey.ca/en/products/detail/eaton-electronics-division/CHSA5930R0002F/16712930
NOTE: The INA228 has two options for the differential input voltage range, Ā±163.84 mV and Ā±40.96 mV. Since we are using a very small resistance, the max Vshunt is expected to be 150 * 0.0002 = 30mV. To obtain a higher resolution, the differential input voltage range should be set to Ā±40.96 mV. This is done by setting the ADCRANGE bit in the CONFIG register to 1.
Pullup Resistors x3
https://www.digikey.ca/en/products/detail/yageo/RC0603JR-1010KL/13694233
Decoupling Capacitor
https://www.digikey.ca/en/products/detail/murata-electronics/GCJ188R71E104KA12D/7363221
Output Connector
Output connector to Pixhawk with I2C current data from INA228 & 5V power from buck converter
https://www.digikey.ca/en/products/detail/molex/5024940670/2380433
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Power Pads
Power pads will be used over XT90 connectors soldered onto board, for the reason of saving weight and space.
The footprint of the power pads can be derived the known XT90 dimensions. The pitch of the XT90 power pads can vary, but shall not exceed 11.00mm in pitch. The recommended wire gauge for XT90 is 10AWG (https://media.digikey.com/pdf/Data Sheets/DFRobot PDFs/FIT0588_Web.pdf), which is 2.588mm in diameter.
Using measurements from a COTS power module, the pad was around 5mm. The measured pitch was 5.6mm.
Having different sources of measurements and dimensions, the WARG XT90 power pads will be 5mm square pads, with a 7mm pitch for the positive and negative leads. This allows for a balance of space to solder the wires onto, so it is neither tight or spaced too far out.
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Stack-Up
The stack-up chosen is the JLC04161H-7628 Stackup, off JLCPCB. The planes are as dictated: PWR-SIG/GND/PWR/GND-SIG.
Stitching Vias
Stitching vias are used to tie the power and ground planes. The stitching for the power planes allows the high current to distribute, allowing the board to handle such large amounts of current. The SaturnPCB tool was used to calculate how much amps each single via can carry, which atleast 50 vias were placed to handle 150A. Tieing the ground places with the stitching vias allows better heat dissipation.
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Addressing Issues
I2C Pull-up
The I2C lines of the IC in the schematic were shorted to 3V3 rail, with no pull-up resistors.
āI removed the pullup resistors since the Pixhawk has its own built in. This is meant to go from the output of the INA228 to the 6-pin connector for the Pixhawk, I connected them through the net names but maybe I did that incorrectly?ā
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Previous Research
Implementation Ideas
āHighā 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 ālow voltage connectorā 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 āhigh voltage passthrough gndā
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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High Level overview of Implementation:
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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.
Output voltage is poproptional to product of current in the conductor and
Linear ICās take continuous range input and outputs and outputs are mostly proportional to the inputs whereas digital ICās output only low or high. Since I will need to take in and output a contiguous range of voltages, I will need a linear IC to get an output voltage that is directly proportional to the magnetic field that interacts with the sensor.
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Hall Effect Sensor Considerations:
Linear: Output voltage can only be up to the saturation voltage that is determined by the power supply. Moving a magnet sideways across a hall effect sensor will give you an increasing analog signal as the pole becomes more and more in aligned with the sensor (doppler effect). An example of this setup is on opposite sides of motors to detect different operating characteristics (RPM, positioning, switches, proximity sensors )
Bipolar Vs Unipolar : Unipolar turns on in the presence of one pole and off when removed whereas in bipolar, it stays on until other pole is introduced.
Advantages of hall effect
No moving parts
Non contact
Low mainteance
Not affected by vibration, dust and water.
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Example of current sense breakout board for ardunio:
https://www.sparkfun.com/datasheets/BreakoutBoards/0712.pdf
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2. Current Sense Transformers:
Current sensing used for control, protection and information.
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2. Analog to Digital Converters (ADC)
Measures ratio of analog input value to a reference value to express in the form of a digital value. The range is divided into n equally sized intervals and each interval is assigned to a certain value.
ADC with 8 unique values gives a resolution of 3 bit (2^N = 8 where N=3 ). Resolution defines the smallest change in input value that the converter can distinguish.
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Offset and gain error can be compensated so that the end and start point of the curve are the same. However, there could be a non-linearity error
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Since this project has stopped active development Iām just posting some random idea links
https://www.digikey.ca/en/products/detail/allegro-microsystems/ACS37612LLUATR-015B5/12093264