1. Power Board for IlliniSat-2 Project
Group 32
Roberto Suarez, Rachit Goel, Sam Kearney
TA: Kevin Bassett
ECE 445 Spring 2013

2. IlliniSat-2 Project Background
Generic bus for a 2 or 3U Cubesat
Systems to communicate with and power payloads
ADACS
Command & Data Handling
Communications
Power
IlliniSat-2 Bus
Model from IlliniSat-2 website: cubesat.ae.illinois.edu

3. Power Board Features Battery Charging/MPPT Battery Protection
Overvoltage/Undervoltage Protection
Cell balancing
Temperature monitoring/regulation
16 DC buses
8 unregulated (7.4V) buses
8 regulated (3.3V) buses
Current Monitoring/Overcurrent Protection

4. Top-Level Block Diagram
Power Lines
Signal Lines
PV Cells Input
Voltage and Current Sense
Battery Charging Circuit (4 switch buck-boost converter)
Voltage and Current Sense
Main Battery
Output to satellite subsystems, payload
Battery Monitoring/ Switching Circuitry
Unregulated Buses x8
Overcurrent Protection
Gate Drive Circuits
Control
Backup Battery
Buck Converter
Regulated
(3.3V) Buses x8

5. Test Boards Main board Battery board Battery charging circuit
Buck converter (7.4V to 3.3V)
2 DC buses (1 unreg, 1 reg) w/ OC protection
Microcontroller
Battery board
Overvoltage/Undervoltage Protection
Cell balancing

6. Battery Charging Circuit
Requirements and specifications:
Input: Spectrolab 28.3% UTJ Solar Cells
7.05 – V (depending on # of cells)
0 – 1.1 A
Output: ___ Lithium Ion Battery Pack
7.4V nominal, 6.0 – 8.2V safe range
Max current 2.2 A
Layout: 2” x 1”
Over 90% efficiency

7. 4-Switch Buck-Boost Converter

8. EPC GaN FET Advantages: Disadvantages:
Small footprint (1.08 mm x 1.7 mm)
High efficiency
low RDS(on) (16 mΩ)
low QG (2.48 nC)
Disadvantages:
Bumped die configuration
very difficult to solder
digikey.com

9. Microcontroller Interfaces: DC bus enable and current measurement
Charge enable/discharge enable for batteries
PWM output for battery charging circuit
Voltage and current measurement on BCC
RTD temperature sensing
Output to Kapton heaters
Communication with C&DH
Implemented on test board
Microchip PIC18F87K22
alliedelectronics.com

10. Maximum Power Point Tracking
Spectrolab UTJ Solar Cells
IV Characteristic
(spectrolab.com)

11. Testing
~8 V P-P

12. Future Work Replacement gate driver: TI LM5113
Gate-source voltage clamped to 5.2 V maximum