Tracking Antenna Nucleo Shield Design

Owned by Hardy Yu
Last updated: 2024-03-12
8 min read

Owner: @Hardy Yu @Nolan Haines

 

Other peripherals on tracking antenna pcb: Tracking Antenna Status & Mechanical/Electrical Components

Power Analysis

XBEE

  • Voltage: 2.8-3.4V

  • Max Current: 50mA (regular version), 250mA (pro version)

RFD900

  • Voltage: 5V

  • Max Current: 1A

BMX160

  • Voltage: 3.3V

  • Max Current: 1.6mA

TBS m8.2

  • Voltage: 3.3V

  • Max Current: 21mA

Servo

  • Voltage: 5V

  • Max Current: 1.5A

Nucleo

  • Voltage: 5V

  • Max Current: 500mA

Features & Design

26V Reverse Polarity Protection - @Nolan Haines

Daniel made a nice write up about RPP for anyone interested: Reverse Polarity Protection Circuits

Leaning towards the Schottky diode solution for RPP. I think this makes sense to reduce cost and complexity, given that for most cases RPP is already accomplished mechanically by the XT60 connectors (which are designed to physically block any reverse connection). I don’t think power consumption is a huge issue in this situation since we’re plugging in 6S batteries which gives us quite a bit of leeway for that.

If we’re going this route, here’s a diode that I think will work: (https://www.digikey.ca/en/products/detail/vishay-general-semiconductor-diodes-division/V6PWM45-M3-I/16683185)

110 C

Recalculation:

For 6A in ambient temperatures, Vf max is 0.58V

P = 6*0.58=3.48W

Thermal resistance = 65C/W

Temp rise = 3.48W*65C/W = 226.2C

We should evaluate this option again

High Side Switch Driver Option

IC: LM74502DDFR

https://www.digikey.com/en/products/detail/texas-instruments/LM74502DDFR/15904171

  • 3.2V-65V input voltage range

  • Up to -65V RPP

2x High Side NMOS

 

Overvoltage protection

  • AOZ2261NQI-12 buck has max VIN of 28V

  • 6S full battery is ~25.2V

  • Set OVP to 27V using

 

Charge Pump VCAP

  • Need to be able to charge input capacitance of both FETs

  •  

  • Input capacitance of AON6236 is 1.225nF

    •  

    • minimum capacitance is 2*1.225*10 = 24.5nF

    • Use 100nF capacitor

EN/UVLO

  • Will use this feature to shutdown the board when a battery lipo cell reaches 3.2V and do low battery indication when battery cell reaches 3.4V

  • LDO

  • Differential Opamp

  • Hysteresis Comparator

    • https://www.digikey.ca/en/products/detail/texas-instruments/LMV7231SQ-NOPB/2434909

      • More likely to use this for undervoltage protection + low battery indicator

        • CO1-CO6 are pulled low when one voltage cell goes below 3.2V

        • COPOL determines if CO1-CO6 go low or go high when the cell voltage is below 3.2V or above 3.4V. Tie COPOL to low.

        • AO goes low when either all the voltage cells are below 3.2V or all the cells are above 3.4V

        • AOSEL determines whether AO goes low when all cells are below 3.2V (tie AOSEL to low) or all above 3.4V (tie AOSEL to high)

          • Basically, CO1-CO6 going low indicates battery is crtitically low and will shutdown and AO going high means at least one voltage cell is below 3.4V (low battery)

      • Use the following case to calculate resistors for window

        • Let dead cell voltage (Vuv) be 3.2V and low battery (Vov) be 3.4V. Differential opamps have a gain of 1/2 so input Vuv and Vov will actually be 1.6V and 1.7V.

        • R3 = 10k

        • R2 = 10k(1.7/1.6-1) = 625

          • Use 620

        • R1 = 10k((1/0.394)1.7-1.7/1.6) = 32.522k

          • Use 32.4k

Input/Output Caps

  • Use 0.1uF input decoupling

  • Use typical 220uF output cap

Overcurrent Protection - @Nolan Haines

IC: TCKE812NA,RF

https://www.digikey.com/en/products/detail/toshiba-semiconductor-and-storage/TCKE812NA-RF/12324959

  • 5V buck has 5A current limit implemented

  • 12V buck has 3+A current limit implemented for short circuit conditions

  • Motor Overcurrent protection

    • Same IC as 12S servo module

    •  

       

    • Have one overcurrent IC for each motor. Limits current to 1.5A per motor using R18

    • C34 controls voltage slew rate which limits inrush current

      • Assuming (worst case scenario) that output capacitance downstream is in the order of 100uF,

      • 1nF cap for dV/dT should safely avoid any OCP triggering

Low Battery Indicator - @Hardy Yu

Requirements:

  • Show the state of the battery without software dependency

  • Turn on a red LED light when the battery drops down to a dangerous voltage

  • Tunable voltage threshold achieved by potentiometer

Component Selection:

IC - @TL431

TI: https://www.ti.com/product/TL431/part-details/TL431ACDBZR

Highlights:

  • Cheap, simple, small, and provide voltage reference

 

10K trimmer potentiometer - @ST-32ETA103

Digikey:https://www.digikey.ca/en/products/detail/nidec-components-corporation/ST-32ETA103/738168

 

Circuit Idea:

 

 

25 to 5V Buck @ 5A - @Nolan Haines

  • Voltage input 26 ~ 15V

  • Output Voltage - clean 5V

  • Max Current @ 5A

Options:

 

Final IC chosen: https://www.digikey.ca/en/products/detail/alpha-omega-semiconductor-inc/AOZ2261NQI-12/16265489

Data sheet: https://aosmd.com/res/data_sheets/AOZ2261NQI-12.pdf

Unless otherwise specified all formulas used here are from the data sheet

 

Caps:

Input Capacitor (C2): https://www.digikey.ca/en/products/detail/murata-electronics/GRM188R61E225KA12J/4905350

∆Vin = 0.03*Vi = 0.75V; Io = 5A; f = 425kHz (see RTON calc below); Cin = ?

Apply formula 6 on page 12 of the datasheet.

Cin = 2.5uF

This capacitor will have an applied DC voltage of 25V. In an X5R cap, this can cause a capacitance drop of 80%. This would make each of the capacitors above have an actual capacitance of ~0.44uF. Thus, we would need 6 of this capacitor in order to get the desired capacitance.

Output Capacitor (C3): https://www.digikey.ca/en/products/detail/samsung-electro-mechanics/CL10A335KP8NNNC/3887550

https://www.digikey.ca/en/products/detail/murata-electronics/GRM188Z71A475KE15J/16602144

NOTE: 4.7uF cap chosen as it is amore common value.

Apply Equation 12 on page 13 of datasheet to determine capacitance. Take an output voltage ripple of 3%.

∆Vout = 0.03*Vout = 0.15V; Io = 5A; f = 425kHz (see RTON calc below); Co = ?

Co = ~3.3uF

This capacitor will have an applied DC voltage of 5V. In an X5R cap, this can cause a capacitance drop of 40%. This would make each of the capacitors above have an actual capacitance of ~2uF. Thus, we would need two of these capacitors to get the desired capacitance.

4.7uF Decoupling Capacitor (C4): https://www.digikey.ca/en/products/detail/murata-electronics/GRM188R6YA475ME15D/4905370

This capacitor will have an applied DC voltage of 5V. In an X5R cap, this can cause a capacitance drop of 40%. This would make each of the capacitors above have an actual capacitance of ~2.8uF. Thus, we would need two of these capacitors to get the desired capacitance.

0.1uF Bootstrap Capacitor (C5): https://www.digikey.ca/en/products/detail/murata-electronics/GCJ188R71C104KA01D/2783813

 

Resistors:

Feedback Resistors:

R1: https://www.digikey.ca/en/products/detail/yageo/RC0603FR-0773K2L/727374

R2: https://www.digikey.ca/en/products/detail/yageo/AC0603FR-1310KL/13694194

https://fscdn.rohm.com/en/products/databook/applinote/ic/power/switching_regulator/resistor_setting_for_vout_appli-e.pdf

Using the formula at the bottom of the first page of the link above, and setting R2 = 10kOhm, we get a value of 73.3333kOhm (reference voltage is 0.6V). We will take the closest standard resistor value which is 73.2kOhm.

100kOhm Input Resistor (R3): https://www.digikey.ca/en/products/detail/yageo/RC0603FR-07100KL/726889

RTON: https://www.digikey.ca/en/products/detail/yageo/RC0603FR-13470KL/13694191

RTON=470kOhms

f = ?

f = Vout/(Vin*TON)

TON(ns) = (RTON(kOhms)/Vin(V)) * 25 = (470/25V) * 25 = 470ns

f = (Vout/(Vin*TON)) * 106 = (5V/(25V*470ns)) * 106 = 425kHz

Using a 470kOhm resistor for RTON will set the frequency to 425kHz.

This frequency is reasonable to keep the inductor within a reasonable size while keeping switching losses down.

Current Limit Resistor (ROCS): https://www.digikey.ca/en/products/detail/yageo/RC0603JR-0718KL/726725

The current limit resistor needs a minimum value of 18k. A current limit resistor of 18k will set a current limit of ~13A.

 

Inductor:

option 1: https://www.digikey.ca/en/products/detail/eaton-electronics-division/EXLA1V0606-6R8-R/16892708

  • pros: small, cheap

  • cons: high DCR

option 2: https://www.digikey.ca/en/products/detail/eaton-electronics-division/DR125-6R8-R/667158

  • pros: cheap, low DCR

  • cons: large

 

Used 30% ripple current.

Vout = 5V, Vin = 25V, f = 425kHz, ∆IL = 0.3*Iout = 0.3*5 = 1.5A

L = (Vout/(f*∆IL))*(1 - (Vout/Vin)) = (5/(425000*1.5))*(1 - (5/25)) = 6.3uH

Peak inductor current = Iout + (∆IL/2) = 5 + (1.5/2) = 5.75A

25 to 12V Buck @ 3A - @Hardy Yu

Requirements:

  • Voltage input 26 ~ 15V

  • Output Voltage - clean 12V

  • Max Current @ 3A

Component Selection:

@ LMR33630

Datasheet: https://www.ti.com/lit/ds/symlink/lmr33630.pdf?ts=1688621693140&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FLMR33630

All different types of the IC: https://www.digikey.ca/en/product-highlight/t/texas-instruments/lmr33630-simple-switcher-buck-converter

Digikey: https://www.digikey.ca/en/products/detail/texas-instruments/LMR33630CDDAR/8554849

Highlight:

  • Input voltage max: 36V

  • Ultra-low EMI

  • efficiency @ 94%

  • Small

Price: $2.07 unit price if buy 10 (maybe we can find the same component with less price?)

Simplified Schematic:

  • According to the datasheet, the component we are choosing, the one with 2.1Mhz switch frequency, will be choosing the connected components with the following number

Inductor Choice:

@ BWVS005050403R3M00

Parameters: 3.3uh 3.5A 2.6mOhms

Digikey: https://www.digikey.ca/en/products/detail/pulse-electronics/BWVS005050403R3M00/12140940

Capacitor Choice:

@ GRM21BZ71H475KE15K

Parameters: 4.7uf X7R 0805 50V

https://www.digikey.ca/en/products/detail/murata-electronics/GRM21BZ71H475KE15K/13904908

@ 06035C105KAT2A

Parameters: 1uf X7R 0603 50V

https://www.digikey.ca/en/products/detail/kyocera-avx/06035C105KAT2A/6564263

@ CL31B106KBHNNNE

Parameters: 10uf X7R 1206 50V

https://www.digikey.ca/en/products/detail/samsung-electro-mechanics/CL31B106KBHNNNE/5961251

 

Use this 10uF cap for input and output capacitance. Same PN as other projects

GRM21BR61H106KE43L

Thermal Design Concerns Reference:

https://www.ti.com/lit/an/slyt793a/slyt793a.pdf?ts=1689862966472

Select Input Capacitor for a Buck Converter Reference:

https://www.ti.com/lit/an/slyt670/slyt670.pdf?ts=1689851310429&ref_url=https%253A%252F%252Fwww.google.com%252F

Shield-Nucleo Interface - @Hardy Yu

 

Connection Solution:

Place long-leg female headers on the shield PCB board such that the headers line up with the relative position on the Nucleo board. This will sacrifice some of the pins and the functionalities along with them from Nucelo board because the female headers from the Nucleo do not represent all the pins. We choose to still go for interface the Shielf with Nucleo through those headers because the number of connectivities provided from those connectors are more than enough for the requirement for tracking antenna

Component Selection:

@ SSW-1??-23-F-D - XX Position Receptacle Connector 0.100" (2.54mm) Through Hole Gold

 

Grouped Output Pinout - @Hardy Yu

 

We don’t want to transport all the connectivities from the Nucleo board to the shield PCB because this is going to significantly increase the complexity of the PCB design.

We the connectivities we want to keep on the shield design -

  • Four UARTs

  • Two SPIs

  • Two I2C

  • Four ADC

  • Eight PWM channels

  • SDMMC

Component Selection:

Four UART and Two I2C pinouts will be using -

@ JST GH connector ( BM04B-GHS-TBT )

https://github.com/pixhawk/Pixhawk-Standards/blob/master/DS-009%20Pixhawk%20Connector%20Standard.pdf

https://www.jst-mfg.com/product/pdf/eng/eGH.pdf

Eight of the PWM pinouts will be using -

@ TSW-101-08-G-T-RA

https://www.digikey.ca/en/products/detail/samtec-inc/TSW-101-08-G-T-RA/6691678

ADC and SPI pinouts will be using -

@ PPPC0?1LFBN-RC / any general female headers

LED Logic - @Hardy Yu

We need:

  • Input Power LED

  • Nucleo Connection LED

  • 5V Rail Output LED

  • 12V Rail Output LED

  • Low Battery Warning LED

 

Component Selection:

Surface Mount Device LED:

@ LTST-C191KGKT

https://www.digikey.ca/en/products/detail/liteon/LTST-C191KGKT/386835

Reason:

  • I saw we have bought it for other boards before, lowkey we can keep using them

 

ADC Low Pass Filter

  • Attenuate signals faster that 1us rise time (attenuate > 350kHz)

  • Will be able to filter fundamental frequency of both bucks (450kHz, 2.1MHz)

  • The STM ADC is used to monitor nominal voltage/current, not transient events

For first order low pass filter, let fcutoff = 400kHz (slightly higher than 350kHz to account for roll-off)

Choose R = 100Ohm

https://www.digikey.ca/en/products/detail/yageo/RC0603FR-07100RL/726888

C = ~4nF

https://www.digikey.ca/en/products/detail/murata-electronics/GCM1885C1H392JA16D/4903747

Input Voltage Sensing

  • Feed voltage divider from input voltage to PA_6 pin (ADC)

Max input voltage: 6S (4.2V*6 = 25.2V), round up to 26V

Use voltage divider

R1 = 68k

https://www.digikey.ca/en/products/detail/yageo/RC0603FR-0768KL/727352

R2 = 10k

https://www.digikey.ca/en/products/detail/yageo/AC0603FR-1310KL/13694194?s=N4IgTCBcDaIIIGEAMA2JBmAYgJQLQEZ18kBpAGRAF0BfIA

Filter to same frequency as ADC above

  • R=68k, therefore C = 20pF

Capacitance so small, place pads but for now don’t put any cap