Requirements
- MUST seamlessly shift between shore power and battery power
- MUST be able to detect the presence of shore power
- MUST wake up APS microcontroller if shore power turned on
- MUST be able to sense if connector is inserted or removed (launch detect)
Some Design Considerations:
If we are using the LTC4007 for the charger chip, we require an Ideal_Diode
- This is essentially a FET with a controller
- FET requires very low Rds_on since it is in the main power path
- Controller must meet thermal requirements so as not to cook the power path controller during operation
- Also needs to handle all stresses that may be encountered during operation
Ideal Diode Transistors:
- After discussing with Andrew and Tim, the Si4422DY will measure up to our requirements:
Si4422DY:
- Datasheet: Si4422DY
- Rds_on = 4.5mOhm
- If we design for 10A
- P = I^2R = 100 x 4.5x10^-3 = 0.45W
Ideal Dioide Controllers:
- Need to handle 30+Volts
- 10A current capability
- fast switching
LTC4357 (Chosen)
- Datasheet: LTC4357
- V range = 9-80V
- Operating current capability 20A
- t-off = 300-500ns
- DFN Package
LTC4412 (In use on current APS)
- Datasheet: LTC4412
- V range = 2.5-28V
- Current Capability 5A (Not enough)
LTC4412HV
- More "rugged" version of the LTC4412
- has a larger max Vin, but still suffers from the 5A current limitation
- Datasheet: LTC4412HV
Functionality
- As can be seen in the LTC4357 datasheet, the IC's IN pin connects to the source of the FET. The source then becomes the anode of the ideal diode. The OUT pin connects to the FET's drain which acts as the ideal diode's cathode. The LTC4357 then detects the voltages at each pin and the gate pin then drives the gate of the FET to maintain the forward drop at 25mV. If the voltage accross IN to OUT becomes more negative than -25mV, the gate of the FET is pulled low with a strong pull down. This would occur in the event that shore power is present.
Component Selection:
Integrated Circuits:
U2101
- Ideal diode controller. See above for functionality
Transistors
Q2104
- Functions as the ideal diode. See above for functionality
Resistors:
R2119
- 10kOhm Pull down for launch detect
Capacitors
C2107
- 39uF bypass capacitor. This value is recommended in the datasheet
C2108, C2109
- 100nF bypass capacitors
Connectotrs
J21??
Shore power connector. Will be updated when Dave has an actual connector. As it stands now this is just an arbitrary 5-pin connector with the followibng connections:
RCKT_RDY
- Connects to the ARM which provides the flight computer with the signal indicating the rocket is ready for launch
SH_TX
- Transmit signal from shore power, this signal will connect to RX of the ARM. In the event of launch, the shore power umbilical will pull out of the connector and this signal will be pulled low by R2119 indicating to the ARM that launch has occurred.
SH_RX
- Recieve signal to shore power, connects to TX of ARM
SH_GND
- Shore power ground
SH_POWER
- Main power from umbilical