Removes a lot of old crufty projects, like the original solar simulator, and design files that are horribly out of date, and some weird backup files.

1u_panel/Design.md

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-# OreSat Solar Module v2

## Everything is Terrible (architecture)

The system architecture of OreSat is weird, and possibly seriously dumb. However, it has a lot of advantages that, despite it's dumbness, are a system-win. One of those dumb ideas that might be either a terrible, terrible mistake or a brilliant stroke of insight (emphasis, possibly, on the stroke) is that the Vbus is based on the Vbat which are two series Lipo cells. Meaning, the Vbus ranges from 6.0 to 8.4 V. Yep. We told you. Brilliant or dumbass. Ask us in 2020 and we'll let you know.

Based on that, we wanted a maximum power point tracer (MPPT) that could take our solar array input and buck/boost that to the 8.4V necessary to charge the battery. Thus there's only one SPS between the array and the batteries, and it's MPPT. A true MPPT, mind you, not one of these namby pamby "70% Voc" maximum power point "controllers".

Finally, we were very interested in a modular array that could stand on it's own, even on a 1U, so we decided to make a single module that stood on its own and could be paralleled with other modules.

## Solar array

The array will be two 27 cm^2 GaAS XTE-SF triple junction solar cells from Spectrolabs, wired together in series. From their datasheet:

    Voc =  Ncells * Voc * = 2 * 2.75V = 5.5V
    Vmp = Ncells * Vmp = 5 * 2.435V = 4.87V
    Isc = 502 mA 
    256 mA with no cover, but we're assuming a cover
    Imp  = 480.6 mA
    Pmax/mp = Vmp * Imp = 4.87 * .481 = 2.3376 W

## MPPT ICs

Requirements:

- (4.0, 4.87, 5.5) V input from the Alta Devices array.
- 6.0 - 8.4 V output connected directly to our LiPo cells -- we don't want a separate battery charger.
- MPPT, not MPPC.

Since there are no COTS ICs that do this, we are unwisely implementing our own MPPT controlled by the onboard uC and the **LT1618** SPS.  The LT1618 is a boost supply with both a CC/CV modes.  The package features a current adjust pin that reads an analog voltage and adjusts the output to a corresponding current, the pin can be grounded for a CV mode.  

Our P/V/I sensors will talk I2C to our uC which will calculate our MPPT, and send an analog voltage to the current adjust pin via an I2C DAC.  This design doubles as our battery charging regulator for the LiPo batteries as well as our MPPT.  

For configuration and parts, see the [LT1618 design notes](LT1618.md).

## Sensor ICs

We choose the TI **INA226** to measure voltage, and current from the solar array.  Current is measured across the same shunt resistor that the LT1618 uses and talks I2C to our uC.   See the [INA226 design notes](INA226.md).

We chose the TI **TMP100** as our temperature sensor.  It comes in an adorable SOT-23 package so we can flip that package upside down and fit the chip into a slot cut into the board so that we can get a more accurate temperature reading of the solar array.  Also has the benefit of working of a wide temperature range and talking I2C to our uC.

**Note: Since the temperature sensor is flipped upside down and fits into a slot in the board, the pins will be flipped from the pinout on the datasheet**

## Microcontroller

For many reasons, we're using the ST **STM32F09x**, which is a 48 LQFP pin Cortex M0 IC which talks CAN. We're using it all over the place on OreSat. And we choose the TI **TCAN330** as the CAN transceiver.

## 3.3 V SPS

After looking at a billion 3.3V switcher ICs, we really like the TI **TPS63070**. The final system footprint is large, but it does buck-boost so that we can get 3.3V even if our batteries are down to their 3.0V minimum voltage. Also, temporary brownouts should be OK given the boost and the giant capacitor banks the TPS63070 requires. See the [TPS63070 design notes](TPS63070.md)

## OreSat Shutdown

The Remove Before Flight (RBF) and rail inhibit switches all need to shut down OreSat. We have an "open collector" shutdown system; pulling the line to ground shuts down OreSat. The STM can decide to shut down it's local panel, too.

We choose regular 1N4448 diodes for the shutdown path because of the horrific leakage current of Schottkey diodes at high temperatures. They leavek **10s of mA!!11!!**. That's a lot. So we choose a silicon diode, run at very low current, so the most the Vf will be is 0.7 V even at very low temperatures.

1u_panel/INA226.md

@@ -1 +0,0 @@
-TBD

1u_panel/LT1618.md

@@ -1 +0,0 @@
-# Analog Devices (Was Linear) LT1618

This "Constant-Current/Constant-Voltage 1.4MHz Step-Up DC/DC Converter" forms the heart of our MPPT. It boosts the Alta Devices ~ 5V five cell array to the 2S battery pack's float voltage of 8.4V. Most critically, the LT1618 "combines a traditional voltage feedback loop and a unique current feedback loop to operate as a constant-current, constant-voltage source". So we'll use the constant-current to program the MPPT.

How is this an MPPT? The LT1618 is capable of both CC and CV modes, where the I for the CC mode is selected via an analog voltage on the Iadj pin (pull to ground for CV).  We already have a V/I sensor along with an M0 microcontroller onboard the panel assembly.  The V/I sensor will constantly be reporting the output of the solar panels to the M0 over I2C, the M0 will calculate the MPP and output an analog voltage to the Iadj pin (via an external I2C DAC) to define a CC output that corresponds with the MPP.  

Here's our existential crisis for the day: by the time we factor in the LT1618 efficiency, and the M0 and associated circuitry, will this be better than literally nothing but a boost supply and a battery charger? A good question. We think yes, the cold hard universe will be sure to let us know.

Some Features we Like:

 - Massive Vin range (1.6V to 18V)
 - 1.4 MHz operating range
 - Current adjust pin that lets us define an I for CC mode or output at CV mode

Features we don't like:

- Operating range of -40 C (good) to +85 C (not quite the +100 C we want)
- Maximum efficiency is only 85%. This is not very good for 2019.
- We'd rather have a synchronous rectifier (switch MOSFET instead of the diode)


## Design Inputs

- Alta Devices 5 cell array at AM0 (assuming PEP cover) 
   - Voc = 5.45 V 
   - Isc = 244 mA
   - Pmp = Vmp = 4.85 V x Imp = 231 mA = 1.12 W
- Height
   - All components must be < 2 mm tall due to component "pockets" cut into the frames.
   - Components may not be placed
      - On thermal interfaces to the frame
      - On top of the card wedge's M2 fasteners, where clearance drops to ???? mm.
- Temperature
   - We expect the solar panels to swing wildly in temperature. All components should be rated for -40 to +100 C.

## Components

References numbers are taken from the LT1618 datasheet, NOT from the solar module.

**D1**

Pick a Schottky diode that minimizes Vf and Ir. Ir becomes a real problem at high temperatures. We arbitrarily choose the ST Micro STPS1L40ZFY(1A, 40V, -40 to +175 C, Vf from 0.3 to 0.4V, Ir = 1 mA @ 125 C typ. and 10 mA max). Analog recommends the On Semi MBRM140 (1A, 40V, weird D0−216AA case, -55 to +125 C, Vf from 0.3 to 0.4V, Ir = 600 uA @ 85 C typ, and 10 mA (!!!) max.) which has almost the exact same performance.

**L1**

Datasheet recommends the SUMIDA CR43NP-100MC (10 +/-20 ％ UH, DCR = 0.182, Irms = 1.04, but 4.8 x 4.3 x 3.5 mm), which is too tall. We choose the BOURNS SRN4018TA-100M (10 +/- 20% uH, Fsrf = 35 MHz, DCR = 0.15 Ohm, Irms/Isat = 1.5A, -55 to +125 C, ferrite core, 4 x 4 x 1.8 mm), which also seems to have better performance.

**Rsense**

We chose 0.1 ohm in an 0603 package. We'll have a maximum of 0.02 V drop and 6 mW power dissipation at Isc. 0402 would have been fine, but in an 0602 package we can eke out a Kelvin connection on the inside of the package. With 0.1 ohms, the constant current limit is set to 50 mV/0.1 ohm = 0.5 A. We could double the resistance and get more signal on the current input, but we don't think we have to and we're trying to maximize efficiency.

**R1/R2 Voltage Selection**

Maximum charge voltage on the 2S pack is 8.4V. Select R2 to be 100k because that seems to be the datasheet's preferred value. R1 = R2 ( Vout / 1.263 - 1) = 565 k. Choose an E96 value of 562K, which gives  Vout = (R1/R2 + 1)*1.263 = 8.36V.

**C1/C2**

The input/output caps are just 0603 4.7 uF caps like in the datasheets. This seems OK, assuming the caps are rated for the temp and voltage (Vwdc >= 16V).


## Operation

Since the DAC on the Iadj input pin is off on power up, the LT1618 starts up with a CV output of 8.4V and a CC of 0.5A. This will instantly brown out the solar panel and cause the LT1618 to shut down and begin to power cycle. Since a boost converter, when off, is just a inductor and diode in series, the LT1618 can't just be disabled on boot. We'll need a switch downstream of the LT1618 (like an LT4412 ideal diode with a disable).

The Iadj pin is used to set the current limit. CC mode happens wht Vi = 50 mV. 

    Imax = 50 mV/Rsense = 0.1 ohm = 0.5 A

With Viadj, this changes to:

    Imax = (1.263V - (0.8)Viadj)/25/Rsense

So the range we can expect here is:

    At Viadj = 0V, Imax = 0.505 A
    At Viadj = 1.579 V, Imax = 0 A

Although the hunt for Pmp is dependent on many variables, we would expect a cold array in full sun to have an output current of ~ 244 mA, which would set an Iadj

    Viadj = (1.263 - Imax x 25 x Rsense)/0.8 = 0.816 V

1u_panel/TPS63070.md

@@ -1,33 +0,0 @@
-# TI TPS63070
-
-> "The TPS6307x is a high efficiency, low quiescent current buck-boost converter suitable for applications where the input voltage can be higher or lower than the output voltage. Output currents can go as high as 2 A in boost mode and in buck mode."
-
-Some featrures we like:
-
-- Vin = 2 to 16V (so we can use 1S to 3S Lipo packs!)
-- Vout = 2.5V to 9V (so we can get a true 3.3V evan with a 3.0V LiPo or a browning out supplies... i.e., it's buck-boost!)
-- -40 to 155 deg C operation
-- 2.4 MHz operation
-- Pretty decent power saving (PFM mode)
-
-## Design Inputs
-
-- Vin is the MPPT output, which is usually 4.2 V
-- Vout is 3.3V, probably < 50 mA peak (and usually < 1 mA)
-
-## Configuration
-
-- EN/PSYNC: Attach to VIN so that it's always enabled and always in PFM mode 
-   - Note; EN compares to 0.8V, could always make a under-voltage test if we wanted to. R11 is there for this reason.
-- VSEL is grounded so it has a non-floating input
-- FB2 is floating (it's just a N CH MOSFET connected to ground)
-- PG is pulled up high because everyone does it. Should be fine to leave floating, but...?
-
-## OreSat component choices
-
-L1 Coilcraft XFL4020-152ME = 1.5 uH 20% 9.1 A AEC-Q200 (4.x 4.3 x 2.1 mm) [link](https://www.mouser.com/productdetail/?qs=VJjuEbE9QBMgot7QvvqAGA%3D%3D)
-C1         = 0603 10uF TBD
-Cin        = 0805 10uF TBD
-C2         = 0603 10uF TBD
-Cout       = 0805 22uF TBD
-

solar_simulator/Eagle/SolarSimulatorPanel.csv

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