Tracking Antenna Nucleo Shield Design
Owner: @Hardy Yu @Nolan Haines
Other peripherals on tracking antenna pcb: https://uwarg-docs.atlassian.net/wiki/spaces/ARCHS22/pages/2263384098
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: https://uwarg-docs.atlassian.net/wiki/spaces/EL/pages/2272002049
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
https://www.digikey.ca/en/products/detail/alpha-omega-semiconductor-inc/AON6236/3060849
Low RDSon (~7mOhm)
40V Vds
+/- 20V Vgs max
Large Id (>15A)
Overvoltage protection
AOZ2261NQI-12 buck has max VIN of 28V
6S full battery is ~25.2V
Set OVP to 27V using
R1 = 100k, R2 = 4.87k (https://www.digikey.ca/en/products/detail/yageo/RC0603FR-074K87L/727217)
Sets voltage limit to 26.92V
R2 not standard, but there is not too much wiggle room between minimum and maximum voltage that OVP can be
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
https://www.digikey.ca/en/products/detail/texas-instruments/TLV76050DBZR/7402852
30V max input, 5V fixed output
100mA
Will need to validate/calculate how much current voltage cell detection requires
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
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
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:
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
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