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DT Uploading Rev A2 Oct 24, 2018
Docs/images readability cleanups Apr 7, 2018
PCB Adding Rev A3, revision used for first prototype run Oct 29, 2018
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.gitignore Starting up work again Oct 3, 2017
Notes Uploading Rev A2 Oct 24, 2018
README.md readability cleanups Apr 7, 2018

README.md

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Main features

  • 1GHz Single board solution using Octavo OSB3358 SIP
  • 6 TMC2130 stepper drivers, stall detection, overcurrent/temp
  • 4 Thermistor or Thermocouple inputs (runtime configurable)
  • 4 high power heater outputs
  • 4 GB fast eMMC
  • Optionally 2 external drivers
  • Direct coupled PRU lines to all drivers
  • Flexible PWM on all 8 MOSFET outputs for flexible EMC passing
  • 4 USB host ports, 1 USB device port
  • 10/100Mbit Ethernet
  • 1080p HDMI
  • Smart power controls
  • Input voltage and current measurement
  • Power removed detection
  • Software defined overcurrent protecion
  • Quad encoder input for filament sensor
  • Buffered end stop inputs, ESD protected connectors
  • 2 Servo outputs
  • Inductive sensor input
  • Two Grove connectors, I2C and UART

A0.png

Power management

Here is an overview of the power distribution power_diagram.png

5V step down TPS54202 calculations

import math
Vout = 5.1 # Output voltage
Vin = 24 # Input voltage
Iout = 2 # Output current
Kind = 0.3 # ?
Fsw = 500000 # Switching frequency
Cbulk = 10 *10**-6
u = 10**6 # micro
L=(Vout*(Vin-Vout))/(Vin*Kind*Iout*Fsw)
print "Inductor selection:"
print "Minimum inductor size: "+str(L*10**6)+" uH"

Lout = 15*10**-6
Ilmax = math.sqrt(Iout**2 + (1/12) + ((Vout*(Vin-Vout))/(Vin*Lout*Fsw*0.8))**2)
print "RMS Inductor current "+str(Ilmax)
Ipeak = Iout + (Vout * (Vin - Vout))/(1.6*Vin*Lout*Fsw)
print "Max inductor current "+str(Ipeak)
print "Choosing NR8040T330M"
Inductor selection:
Minimum inductor size: 13.3875 uH
RMS Inductor current 2.10904312204
Max inductor current 2.3346875
Choosing NR8040T330M
dIout = 0.7
dVout = 0.2 # Delta voltage with dI
Vr = 0.03 # Ripple Voltage
Ir = Iout*0.3
CO1 = (2*dIout)/(Fsw*dVout)
CO2 = (1.0/(8.0*Fsw))*(1.0/(Vr/Ir))
#CO3 =
print "Input Capacitor Selection:"
print "CO1: "+str(CO1*u) + " uF"
print "CO2: "+str(CO2*u) + " uF"

#print "Minimum capacitance: "+str(CO*u)+" uF"
print "Choosing 20uF"
Input Capacitor Selection:
CO1: 14.0 uF
CO2: 5.0 uF
Choosing 20uF
R2 = 100.0*10**3
R3 = 13.3*10**3
Vref = 0.596
Vout = Vref*((R2/R3)+1)
print "Calculation of output resistance: "
print "Vout = "+str(Vout)
Calculation of output resistance:
Vout = 5.07720300752

Stepper drivers

Current sense resistor:

R = 0.1
I = 1
U = R*I
P = U*I
print "Power dissipation: "+str(P)
Power dissipation: 0.1

Diagnostics:

$2*8 = 16$
  • Connect together to form a single interrupt? No, it's good to have individual pins for stallguard.

Capacitor selection

  • 100uF electrolytic capacitor is recommended. No mention of ESR or ripple current in the TMC2130 data sheet.
  • What is the frequency at which the largest current draw is expected?
  • There are 10uF capacitors in line to handle high frequency current draws, so it is expected that the electrolytic capacitors will handle lower frequecy draws. It depends on cable length, ESR in PSU as well.

SPI and enable

  • Enable pins, can it be done using SPI?
  • SPI CS pins, need 8 pins at least.
    • Use Mux?
      • Increased cost. How much?
    • Daisy chain?
      • What is the required time?
      • Not good for Stepper A/B. Use CN1?
      • Each transaction takes 60 us
    • Individual pins.
      • Requires 8 pins.
print "Stepper readout time: "
a = 6.0*40/(4*10**6)
print "it takes "+str(a*u)+" us for each transaction"
Stepper readout time:
it takes 60.0 us for each transaction

PWM calculations

Current setting

  • Use PWM chip?
    • Costly > $1
    • board space
  • Use internal reference
    • 5 bit precision
print "Number of current steps on TMC2130: "+str(2**5)
Number of current steps on TMC2130: 32

Smart input current monitor circuit.

Fuses have slow responses, so they do not protect against short circuits and only asymptotically approach their rating with time. They are temperature dependent, difficult to replace, and physically large. They also increase manufacturing time and cost due to almost universally being through-hole components.

  • Measure input voltage
  • Measure input current.
  • Choosing PMOS to also implement power lost detection.
  • Reverse polarity protection
R = 0.001
A = 30
adc_vals = 2**12
v_adc = 1.8
v_res = R*A
Gain = 50
resolution =(v_adc/adc_vals)/R/Gain

print "Over current calculations:"
print "Max current: "+str(A)+" A"
print "Resistor value: "+str(R*1000)+" mOhm"
print "Voltage drop across resistor: "+str(v_res*1000)+" mV"
print "Voltage measured: "+str(v_res*Gain)
print "Power dissipation in Rsense: "+str(R*A*A)+" W"
print "resolution: "+str(resolution*1000)+" mA"
Over current calculations:
Max current: 30 A
Resistor value: 1.0 mOhm
Voltage drop across resistor: 30.0 mV
Voltage measured: 1.5
Power dissipation in Rsense: 0.9 W
resolution: 8.7890625 mA
v_max = 24
R1 = 100*10**3
R2 = 4.7*10**3
print "Input voltage calculations: "
print "Voltage divider max output: "+str(v_max*R2/(R1+R2))
print "Input voltage resolution: ??"
Input voltage calculations:
Voltage divider max output: 1.07736389685
Input voltage resolution: ??
Imax = 30
RDS = 5.6*10**-3
Ploss = RDS*Imax*Imax
print "Input P-mos power calculations:"
print "Power expenditure: "+str(Ploss)+ " W"
Input P-mos power calculations:
Power expenditure: 5.04 W

ESD considerations

  • EN 55024/EN 61000-4-2: ±4kV Contact, ±8kV Air

Board

  • Ground shield, having 0.1R to ground.

USB

  • Using TPD4S012 having Contact: ±10kV, Air: ±10kV

HDMI

Ethernet

  • Isolated using magnetics.

Endstops

  • Input buffer CD4050BD with HBD: ±1500, CDM: ±1000

Analog

  • Series resistance

Steppers

  • TMC2130 HBM: ±4 kV

Heater MOSFETs

  • 4.7nF protection

Fan MOSFETS

  • No protection

Layout considerations

Using en562748 as reference for PHY layout.

  • Using 100R resistors in series to reduce EMI.
  • Placing PHY chip close to SIP since differential lines radiate less than 3.3V single ended lines.
  • Removing ground plane under magnetics.
  • 100 Ohm differential impedance
  • Place 49.9ohm pullups close to PHY chip.
  • OSH park uses FR408 laminate
Er = 3.67 # Relative dielectric costant
H = 0.17018 # prepreg height in mm
T = 0.035 # Copper thickness (mm)
F = 125 # Frequency MHz
print "0.15/0.15 track and gap gives 98.4 differential and 65.3 single ended"
0.15/0.15 track and gap gives 98.4 differential and 65.3 single ended
Vf = 2.8 # Diode forward voltage drop (V)
Vin = 3.3 # Input voltage (V)
Vres = Vin-Vf
If = 0.0001 # Diode current, 1mA
R = Vres/If
print "LED power calculations: "
print "Resistor for {}, {}mA: {}".format(Vin, If*1000,R)
LED power calculations:
Resistor for 3.3, 0.1mA: 5000.0

Sysboot config

Two Boot modes: MMC1 or USB device

  • SYSBOOT[15-14] = 10b = 25MHz
  • SYSBOOT[13:12] = 00b = reserved
  • SYSBOOT[11:10] = xx
  • SYSBOOT[9] = xx
  • SYSBOOT[8] = xx
  • SYSBOOT[7-6] = xx
  • SYSBOOT[5] = 0b = Disable CLKOUT1
  • SYSBOOT[4:0] = 11100b = MMC1, MMC0, UART0, USB0

To boot from USB:

  • SYSBOOT[4:0] = 11000b = SPI0, MMCO0, USB0, UART0
Imax = 1.5 # Maximum output current on all 4 USB ports
Rmeas = 0.01 # Current measurement resistor on low side.
RDSon = 0.065 #P-mos RDSon
Vin = 5.1
Vdrop = Vin - (Rmeas + RDSon)*Imax
print "Voltage drop across R: {}".format(Rmeas*Imax)
print "Resulting voltage to USB: {}".format(Vdrop)
Voltage drop across R: 0.015
Resulting voltage to USB: 4.9875
Imax = 1.5 # Maximum output current on all 4 USB ports
Rmeas = 0.01 # Current measurement resistor on low side.
RDSon = 0.065 #P-mos RDSon
Vin = 5.1
Vdrop = Vin - (Rmeas + RDSon)*Imax
print "Voltage drop across R: {}".format(Rmeas*Imax)
print "Resulting voltage to USB: {}".format(Vdrop)
Voltage drop across R: 0.015
Resulting voltage to USB: 4.9875

Review

  • Changed vias to tented
  • Moved pin 1 indicator on U2
  • Moved all test points to top side
from IPython.display import display, Markdown, Latex

Calculation of power dissipation of P-MOS

  • $R_{ds(on)max} = 45 m\Omega$ @ $-10 V$
  • Thermal Resistance, Junction to Ambient @ $TA=+25 ^{\circ}C$ is $R_{\theta JA}=26 ^{\circ}C/W$
Von=6
Ta=25
Imax=30
#Imax=2
Rdson=0.0045
TR=26

# P=I^2*R
P=Imax*Imax*Rdson

Trise=TR*P
T=Ta+Trise

display(Markdown("""
$P={P:0.3f} W$\n
$T_{{rise}} = {Trise} ^{{\circ}}C$\n
$T = T_A + T_{{rise}} = {T:0.3f} ^{{\circ}}C$ when $I={I:.0f} A$

""".format(P=P, Trise=Trise, T=T, I=Imax)))
$P=4.050 W$

$T_{rise} = 105.3 ^{\circ}C$

$T = T_A + T_{rise} = 130.300 ^{\circ}C$ when $I=30 A$