PSAS/ avionics/ av3-generic-front-end

Design notes for the AV3 node "Generic Front End" (GFE) circuit and PCB.

A GFE Board


AV3 stands for "Avionics System 3", our fourth generation of avionics systems for amateur rockets (it's zero based, of course). "Generic Front End" means that this circuit, and most of the layout, is replicated across the ~8 nodes found in the avionics system. The GFE contains three sections:


LV0, LV1 had (woefully underpowered) monolithic flight computers (FC). LV2 had an FC with many CAN-based Microchip PIC18 nodes. This revision, now called "AV" instead of "LV" in order to separate it from launch vehicle, is now based on USB and CAN, and uses the NXP LPC2368 ARM7TDMI microcontroller.

Original work on this board was done using the USB-only NXP LPC2148 by the PSU ECE Capstone 2006 team and can be found here. This board was significantly revised by adding the CAN and USB-based NXP LPC2368 by the Capstone 2009 team and can be found here.

GFE Requirements

Design Notes

Left to do:

Use Cases

Vout Requirements What to do
3.3 V, battery back up Leave the circuit as is.
3.3 V, no battery Rip out the entire HAP circuit and connect 3.3V plane via 'SPS/3.3V'.
3.3V, 5 V, no battery Leave SPS at 5V, bypass the battery circuit, leave HAP at 3.3V output.
3.3V, 5 V, battery Leave the circuit as is but attempt to get "hack" 5V supply off HAP IC to work.

Component Values

Most of these entries come directly from the Capstone 2006 and 2009 component entries.

The component numbers are as follows (see RocketNames):

Section Numbers
SPS 2000 - 2099
HAP 2100 - 2199
UC 2200 - 2299

Each components should have three lines:


J2000 Rocketbus connector

R2000 chassis ground isolation resistor

C2000 chassis ground bypass capacitor

L2000 input choke

F2000 fuse

C2001 bulk charge filter capacitor

C2002 filter capacitor

C2011 filter capacitor

TVS2000 transient and over voltage supressor

Q2001 UVL/OVP/OVC switch

R2003 shunt resistor

U2000 circuit breaker chip

R2001 UVLO resistor divider of U2000

R2002 UVLO resistor divider of U2000.

Q2000 SPS off command from LPC

R2012 Pulldown resistor for Q2000

R2004 over-voltage protection buffer

Q2002 over-voltage protection switch

U2001 Over-voltage protection comparator

C2003 Backup power for U2001

D2001 Backup power for U2001

R2005 SPS OVP divider network 1 of 2

R2006 SPS OVP divider networkh 2 of 2

C2004 LPF cap on SPS OVP divider


U2002 buck regulator

C2005 Input Capacitor Cin1

C2006 Input Capacitor Cin2

R2007 soft start resistor @ LT3972 'RUN/SS' pin

C2007 soft start capacitor

R2008 frequency compensation resistor @ LT3972 'Vc' pin

C2008 frequency compensation capacitor @ LT3972 'Vc' pin

R2009 frequency set resistor @ LT3972 'RT' pin

C2009 Boost and Bias Capacitor

D2002 catch diode

L2001 SPS buck Inductor

R2011 Feedback resistor R2 for U2002

R2010 Feedback resistor R1 for U2002

C2010 Output Capacitor for U2002


U2100 HAP Battery charger & power control

Q2100 External power ideal diode

R2102 Q2100 pull up

R2100 PROG resistor

R2101 CLPROG resistor

C2100 Charge Timer Capacitor

Q2101 Battery power ideal diode

RT2100 Battery temperature thermistor

R2103 Thermistor Rnom

R2104 Thermistor Rdelta

LED2100 Red charge LED

R2105 Charge LED resistor

R2112 PORT1.10 protection resistor

B2100 HAP battery


U2102 TPS63000 buck-boot supply

C2101 Bulk input capacitor

C2102 bypass cap

U2102 HAP shutdown latch

R2107 U2102 clock pull down

R2108 Startup delay resistor (?)

C2103 Startup delay capacitor (?)

R2109 U2101 feedback resistor divider 1 of 2

R2110 U2101 Feedback resistor divider 2 of 2

C2104 Feed-forward capacitor

L2100 HAP output inductor

C2105 HAP supply bulk output cap (1/2)

C2108 HAP supply bulk output cap (2/2)


LED2101 Amber 3.3V on LED

R2111 Charge LED resistor

D2100 HAP "secondary" Buck (Catch) Schottky Diode

C2106 HAP "secondary" buck filter cap (1 of 2)

C2107 HAP "secondary" buck filter cap (2 of 2)



Q2200, Q2201 RGB LED driver

R2205, R2206, R2207

U2203 Clock divider for SPS and HAP

J2204 debug connector

TVS2200, TVS2201 Surge protectors

L2200, L2201 "T" EMI filter

U2200 LPC2368

X2201 12 MHz crystal

X2200 32.768 KHz crystal

U2201 CAN driver

D2201, D2202 CAN disconnect "OR"ing diodes

R2203 CAN disconnect pulldown

U2202 Triple Schmit inverters for CAN stuck-dominant bit

D2200 Stuck dominant bit diode

R2202 Stuck dominant bit timer resistor

C2200 Stuck dominant bit timer capacitor

Design log


Fabbed the boards and got them back! Gerbers that were fabbed were in git commit 5f6bbb58075a9bea24e6dde172e43951f1043f0d. Issues so far: