Power Distribution Board (PDB) - Unarchived

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

https://holybro.com/products/pm03d-power-module?pr_prod_strat=e5_desc&pr_rec_id=eefeb6967&pr_rec_pid=7192462491837&pr_ref_pid=7408912400573&pr_seq=uniform

https://holybro.com/products/pixhawk-4-power-module-pm07?pr_prod_strat=e5_desc&pr_rec_id=096753d49&pr_rec_pid=7150469939389&pr_ref_pid=7192462491837&pr_seq=uniform

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

Component

Specifications

image-20250307-053457.png

https://www.digikey.ca/en/products/detail/texas-instruments/TPS54360BDDAR/10434703

  • Vin: 4.5V - 60V

  • Vout: 0.8V - 0.92 X Vin

  • Iout: 3.5A continuous

  • Switching Frequency: 100 kHz - 2 MHz adjustable

  • Efficiency: ~ 91% @ 48V

  • Unit Price: $4.32 ($3.01 for >25 order quantity)

image-20250228-231817.png

https://www.digikey.ca/en/products/detail/vishay-siliconix/SIC463ED-T1-GE3/7616336

  • Vin: 4.5V - 60V

  • Vout: 0.8V - 0.92 X Vin

  • Iout: 4A continuous

  • Switching Frequency: 100 kHz - 2 MHz adjustable

  • Efficiency: ~ 91% @ 48V

  • Unit Price: $3.28 TR, $6.10 CT

image-20250228-233034.png

https://www.digikey.ca/en/products/detail/analog-devices-inc-maxim-integrated/MAX17576ATG-T/11485132

  • Vin: 4.5V - 60V

  • Vout: 4.75V - 5.25V

  • Iout: 4A

  • Switching Frequency: 100 kHz, 500kHz, 2.2MHz adjustable

  • Efficiency: ~ 87% @ 40-50V

  • Unit Price: $5.98 TR, $13.81 CT

image-20250301-003545.png

https://www.digikey.ca/en/products/detail/texas-instruments/TPS54560DDAR/3929556

  • Vin: 4.5V - 60V

  • Vout: 0.8V - 58.8V

  • Iout: 5A

  • Switching Frequency: 100 kHz - 2.5 MHz adjustable

  • Efficiency: ~ 84% @ 48V

  • Unit Price: $4.46 TR, $8.04 CT

image-20250307-173240.png

RT6365GSP | Richtek Tech | DC-DC Converters | JLCPCB

  • Vin: 4.5V - 60V

  • Vout: 0.8V - VIN

  • Iout: 5A

  • Switching Frequency: 100 kHz - 2.5 MHz adjustable

  • Efficiency: ~ 84% @ 48V

  • Unit Price: $1.065

image-20250307-174015.png

TPS54360BDDAR | Texas Instruments | DC-DC Converters | JLCPCB

  • Vin: 4.5V - 60V

  • Vout: 0.8V - 58.8V

  • Iout: 3.5A

  • Switching Frequency: 100 kHz - 2.5 MHz adjustable

  • Efficiency: ~ 82% @ 48V

  • Unit Price: $0.84

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

image-20250313-032923.png
Simplified Schematic
image-20250312-125900.png
Example Application

IC Pinout

image-20250310-230256.png

Frequency Setting Resistor

The switching frequency of the TPS54360B is adjustable from 100 kHz - 2500 kHz by placing a resistor between the RT/CLK pin and GND pin.

image-20250313-010704.png
image-20250313-010721.png

I O - output current

I CL - current limit

R dc - inductor resistance

V IN - maximum input voltage

V OUT - output voltage

V OUTSC - output voltage during short

V d - diode voltage drop

R DS(on) - switch on resistance

t ON - controllable on time

f DIV - frequency divide equals (1, 2, 4,or 8)

The above 2 equations calculate the upper limit of the switching frequency for the regulator. Switching frequencies higher than these values results in pulse skipping or the lack of overcurrent protection during a short circuit.

image-20250313-012310.png

Output Feedback Voltage Divider

image-20250310-230544.png

Output Inductor Selection

  1. Inductance > minimum output inductance

image-20250310-231711.png

L O(min) - minimum output inductance

K IND - inductor ripple current : maximum output current ratio

V OUT - output voltage

I OUT - output current

V IN(max) - maximum input voltage

f SW - switching frequency

 

  1. RMS current < RMS current rating

image-20250311-002557.png

I L(rms) - RMS inductor current

I OUT - output current

V OUT - output voltage

V IN(max) - maximum input voltage

L O - output inductance

f SW - switching frequency

 

  1. Maximum current < saturation current rating

image-20250311-004627.png

I RIPPLE - ripple inductor current

V OUT - output voltage

V IN(max) - maximum input voltage

L O - output inductance

f SW - switching frequency

image-20250311-002614.png

I L(peak) - peak inductor current

I OUT - output inductance

I RIPPLE - inductor ripple current

Input Capacitor Selection

  • Ceramic X5R or X7R input decoupling capacitor with at least 3 μF of effective capacitance

  • Voltage rating > maximum input voltage

  • Ripple voltage within 1-3% V OUT

image-20250314-030425.png
Ripple Voltage
  • 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

      • image-20250326-182437.png
    • 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

The output capacitor value determines “the modulator pole, the output voltage ripple, and how the regulator responds to a large change in load current.”

  1. A recommended Cout > 29.2uF to account for transient load response

  2. The output capacitance must be able to supply difference in current for 2 clock cycles to maintain the output voltage within the specified range. ESR for ceramic capacitors is negligible, however, it must be included in load step calculations for aluminum electrolytic and tantalum capacitors.

 

image-20250310-234252.png

△I OUT - change in output current

△V OUT - allowable change in output voltage

f SW - switching frequency

 

  1. The output capacitance must be able to keep the output voltage overshoot--energy stored in inductor from high to low load current---to a desired value.

image-20250310-234743.png

I OH - output current under heavy load

I OL - output under light load

V f - peak output voltage

V i - initial voltage

 

  1. The output capacitance must be able to meet the output voltage ripple specification.

image-20250310-234838.png

f SW - switching frequency

V ORIPPLE - allowable output voltage ripple

I RIPPLE - inductor ripple current

 

  1. The output capacitor’s ESR value must not exceed output voltage ripple specification.

image-20250310-235631.png

 

V ORIPPLE - maximum allowable output voltage ripple

I RIPPLE - inductor ripple current

 

  1. The output capacitor’s maximum ripple current must be able to support RMS ripple current.

image-20250310-235722.png

V OUT - output voltage

V IN(max) - maximum input voltage

L O - output inductance

f SW - switching frequency

  • 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)

      image-20250314-011053.png
  • 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

    • image-20250313-165405.png
  • 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

    • image-20250330-152112.png

 

Catch Diode

An external catch diode between the SW pin and GND is required.

  • Reverse voltage rating ≥ Maximum input voltage, V IN(max) required

  • Peak current rating ≥ Maximum inductor current required

  • Lower forward voltage drop for greater efficiency

Compensation

  • Type 2 circuits: high bandwidth power-supply designs using low ESR output capacitors

    • Using Type 2A since we are using ceramic capacitors

  • Type 1 circuit: high-ESR aluminum electrolytic or tantalum capacitors

image-20250320-215359.png
image-20250313-170524.png
image-20250313-170539.png

Use the smaller f co

image-20250313-170548.png
image-20250313-170605.png
image-20250313-170616.png
image-20250313-170627.png

Use the larger C 8, C 8 is the additional compensation pole in Type 2A (as opposed to 2B)

image-20250322-024605.png
image-20250322-015342.png

UVLO Voltage Divider

When EN is left to float:

  • EN pin has an internal pullup current source i1 of 1.2uA

  • IC enabled when V IN > 4.3V and V EN > 1.2V

    • I hys = 3.4uA

  • IC disabled when V IN < 4V or V EN < 1.2V

    • Ihys = 0

  • Maximum EN pin voltage: V EN > 8.4V

    • Recommended to use a zener diode to clamp pin voltage below abs. max. rating

image-20250320-213912.png
image-20250313-170218.png
image-20250313-170230.png
  • For 12V, 5V, 3V3 - 8V outputs, use: N/A

Bootstrap Capacitor Selection

  • A 0.1-μF ceramic capacitor must be connected between the BOOT and SW pins

  • ≥ X5R grade dielectric recommended

  • ≥ 10 V or higher voltage rating required

Over Current Protection (OCP) - EFUSE

LS1205EVD33

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.

image-20250307-144052.png
Placement of magnetic sensor.

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

https://www.digikey.ca/en/products/filter/linear-compass-ics/554?s=N4IgTCBcDaILYEMDmA7ApgFwJYGMAEAzmigQPYBOIAugL5A

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

image-20250324-193737.png
Location of Hall element.

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