Power Distribution Board (PDB) - Unarchived
Introduction
Engineer(s):
@Andrew Chai PM, Design Architecture, SMPS
@Kenny Na Sensing + Interface, Design Architecture
@Megan Lee Sensing + Interface, SMPS
@Santosh Erathasari OCP/Short-Circuit Protection, SMPS
Background:
Unarchived project from the 2024 PDB 12S PDB
A power distribution board (PDB) is used for supplying and distributing power form the main power supply to various circuits and subsystems. In a drone/UAV context, the PDB is responsible for converting and distributing the battery pack voltage to the several electronics on the drone itself.
Reference COTS PDBs:
PDB500[X] ← this is the one being used on Big Quad 2025
What:
Handle 12S input range (40V-50V)
12V & 5V output rails with sufficient current output for downstream electronics
Common voltage rails
Standard connector
Reverse Polarity Protection (RPP)
Short Circuit Protection??
Voltage + Current Sense → maybe need CAN adapter circuit??
high current passthrough (may be difficult if this is taking in the entire bus current)
might be nice to have a discrete implementation of this, as well as I-sense for each rail
Sensing IC without shunt resistor
Redundancy Support (having just one supply rail makes the system single fault susceptible)
Not deemed as important
Proper input + output filtering networks (need to avoid resonant frequency of Li-Po batteries)
High efficiency power conversion system
Can try playing around with different ways to optimize for efficiency ie soft switching, IC selection
Block Diagram
System Requirements
https://uwarg-docs.atlassian.net/wiki/spaces/ARCHS22/pages/2964520964
Power Budget^^
12V @ 3-4A
5V @ 3-4A @Megan Lee
3V3-8V @ 1-2A @Santosh Erathasari
3V3_analog LDO <1A
Nice to have short circuit protection on LV rails
Switch Mode Power Supply
Buck Converter ICs
Andrew, Santosh, Megan
Component | Specifications |
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https://www.digikey.ca/en/products/detail/texas-instruments/TPS54360BDDAR/10434703 |
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https://www.digikey.ca/en/products/detail/vishay-siliconix/SIC463ED-T1-GE3/7616336 |
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https://www.digikey.ca/en/products/detail/analog-devices-inc-maxim-integrated/MAX17576ATG-T/11485132 |
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https://www.digikey.ca/en/products/detail/texas-instruments/TPS54560DDAR/3929556 |
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TPS54360BDDAR | Texas Instruments | DC-DC Converters | JLCPCB |
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Since we likely won’t need > 3A on some of the rails, a 3.5A output current should be sufficient. TPS54360BDDAR has an adjustable switching frequency that goes up to 2MHz so we can make our design pretty compact. It also has a simpler application circuit..?
Andrew 12S to 12V Calculations
Typical Application Circuit
IC Pinout
Frequency Setting Resistor
For 12V output, use: 735kHz
RT = 133k
For 5V output, use: 800kHz
Place in R T1 & R T2 in series for R T
For 3V3 output, use: 802kHz
Output Feedback Voltage Divider
For 12V output, use:
R HS = 147k
R LS = 10.5k
For 5V output, use:
R HS = 29.4k → 30k, https://jlcpcb.com/partdetail/23711-0603WAF3002T5E/C22984
R LS = 5.6k, https://jlcpcb.com/partdetail/23916-0603WAF5601T5E/C23189
Note: will output approx. 5.08 - 5.09V
For 3V3 - 8V output, use:
Output Inductor Selection
For the 12V output, use: https://www.digikey.com/en/products/detail/tdk-corporation/SPM10065VT-330M-D/12175283?s=N4IgTCBcDaIMoAUCyBGADGgbAVgGoBUBaAZmLSUIBEAdakAXQF8g
L = 33uH
4.9A Current rating
59 mOhms DCR
6.5A Saturation current
10.5mm x 10mm
For the 5V output, use: https://www.digikey.ca/short/7hq0f4pt
L = 8.2 uH
4.5A current rating
6A saturation current rating
60mOhms DCR
73 x 6.6mm
For the 3V3 - 8V output, use: https://www.digikey.ca/en/products/detail/bourns-inc/SDE0805A-100M/5030885
L = 10uH
3.2A current rating
2.6A saturation current rating
50mOhm DCR
7.8mm x 7.0mm
Input Capacitor Selection
For the 12V output, use:https://www.digikey.ca/short/qmw87ww3
~Each 10uF, 100V input cap provides around 2.5uF input capacitance at 12S nominal
Calculating for inductor current ripple yields around 0.376A
At 3.5A, 735kHz switch frequency (scales linearly with increasing input capacitance/decreasing output current):
5uF Cin gives ~173mV ripple
7.5uF Cin gives ~116mV ripple
10uF Cin gives ~87mV ripple
For the 5V output, use: https://www.digikey.ca/short/qmw87ww3
X7S temperature coefficient
100V voltage rating
5 x 10uF in parallel → 12.56uF @ 50V DC bias
32mV voltage ripple
R ESR = 20mV @ 800kHz
For the 3V3- 8V output, use: https://www.digikey.ca/en/products/detail/murata-electronics/GRJ31CZ72A475KE01L/16033704
for 3V3 output, the desired ripple voltage is between 10-20mV.
at 1.5A and 800Khz switch frequency
Cin = 10uF =>11.5mV ripple voltage
X7R Ceramic Capacitor is desired
DC Bias:
4.7uF +-10% at 50V → only at 55% so 2.585uF
4 caps in parrallel = 10.34uF
100V rating
Iout = 1.5A
Output Capacitor Selection
For 12V output, use: https://www.digikey.ca/short/rt48r07n & https://jlcpcb.com/partdetail/6567201-GRM32ER71E226KE15K/C5646288
At 12V DC bias, the 22uF, 25V capacitors are derated to 9.165uF
4x in parallel gives 36.66uF
Using the standard estimation of ripple current of ~0.3Iout, at 3A ripple voltage is ~3mV (scales linearly with output current, as output current increases, voltage ripple increases)
For 5V output, use: https://www.digikey.ca/en/products/detail/murata-electronics/GRM31CR61A476ME15L/2334879?s=N4IgTCBcDaIOICUCyBmAjAYQQNjQQQBYB2bJAUTQFYAZEAXQF8g & https://jlcpcb.com/partdetail/MurataElectronics-GRM31CR61A476ME15L/C94034
10V voltage rating
2 x 47uF in parallel → 37.456 at 5V DC bias
At 3A, with ripple current of ~0.34Iout, ripple voltage is ~4mV
For 3V3 - 8V output, use: https://www.digikey.ca/en/products/detail/murata-electronics/GRM21BR61E106KA73L/2334874
For 3V3 low output ripple is important: https://www.richtek.com/Design%20Support/Technical%20Document/AN014?sc_lang=en
Output ripple should be <<1% of Vo. 1.6mV of ripple (about 0.05% of Vo) @3V3 output
Output ripple of 3.5mV @8V output
Ripple Current at 0.3Io, and the specified 10uH L, we pick Co to be 45uF
Accounting for DC bias we 7.286uFx5 = 36.43uF
Catch Diode
For 12V, 5V, 3V3 - 8V outputs, use: https://www.digikey.ca/en/products/detail/panjit-international-inc/SK56L-R1-00001/14660240?s=N4IgTCBcDaIMoGkCsA2AMgfQEoEYMAZD8cQBdAXyA & https://jlcpcb.com/partdetail/PanjitInternational-SK56L_R1_00001/C294834
60V reverse voltage rating
5A peak current rating
375mV @3.5A forward voltage drop
Compensation
For 12V output, use:
For 5V output, use:
R 4 =30k
C 5 = 4.43nF → standard capacitor value, 4.7nF
C 8 = 32.9pF → standard capacitor value, 33pF
For 3V3 - 8V output, use:
C8 = 36pF = 18pf + 18pf (in parallel): https://jlcpcb.com/partdetail/1999-CL10C180JB8NNNC/C1647
C5 = 2.7nf: https://jlcpcb.com/partdetail/1961-0603B272K500NT/C1609
R4 = 18.7k https://jlcpcb.com/partdetail/23620-0603WAF1872T5E/C22893
UVLO Voltage Divider
For 12V, 5V, 3V3 - 8V outputs, use: N/A
Bootstrap Capacitor Selection
For 12V, 5V, 3V3 - 8V outputs, use:
Over Current Protection (OCP) - EFUSE
https://www.digikey.com/en/products/detail/littelfuse-inc/LS1205EVD33/16680651
Input Voltage between 2.7V to 18V
Max Safe Current: 5A (Programmable)
25mOhm Rdson
Current + Voltage Sense
@Kenny Na
Our PDB does not offer battery passthrough to the ESCs, so a typical full load scenario on the PDB may call for over 10A being delivered at 12S potential (~44V nominal, pretty much 48V). At this voltage and current, a shunt resistor-based sensing configuration may cause enough power loss to be something to consider. We can look into passive options for sensing, including using magnetic Hall effect sensors.
Hall Effect Sensing
The idea is grounded in electromagnetism - place an inductive element in the path of a changing magnetic field, and measure the induced voltage.
This makes the best placement of the IC on top of the trace delivering the current to be sensed. Ideally, the power trace is uniform in shape and the path of current is distributed evenly. This may be verified with PDN simulation and analysis.
Our power budget:
12V @ 3-4A
5V @ 3-4A
3V3 @ 1-2A
3V3_analog LDO <1A
If we want to sense the entire system current usage, we can assume around 10 to 11 Amps maximum draw. Assuming the PCB trace being sensed is straight and ~0.2mm away, we can use Ampere’s Law:
∮ B ⋅ dl = μ0Ienc
∮ B ⋅ dl = B(2πr) = μ0Ienc
B = μ0Ienc / 2πr
B = (4π x 10-7)(10)/2π(0.2 x 10-3)
B = 0.01 T = 10 mT
IC Selection
Our sensing is one dimensional and we can save costs by picking a 1-dimensional (linear) magnetic sensor. Alternatively, we can pick more expensive ICs with a dedicated SMBus interface or additional sensing capabilities. This depends quite heavily on the proximity of the microcontroller and the risk of noise coupling into the analog output from the sensor.
https://www.digikey.ca/en/products/detail/texas-instruments/DRV5055A1QDBZR/8567407
Analog sensor, analog output
±21 mT sensing range
12.5 mV/mT sensitivity
r = (650 - 80) um + 0.0127 mm (0.5 mils; example solder mask thickness)
r = ~ 0.58 mm
B = (4π x 10-7)(10)/2π(0.58 x 10-3)
B = 0.003448 T or 3.34 mT
Useful Resources/Links
Buck Converters: https://uwarg-docs.atlassian.net/wiki/spaces/EL/pages/1931313166
RPP: https://uwarg-docs.atlassian.net/wiki/spaces/EL/pages/2272002049
MOSFETS: https://uwarg-docs.atlassian.net/wiki/spaces/EL/pages/2318532681
CAN Circuit: https://uwarg-docs.atlassian.net/wiki/spaces/EL/pages/2524119043