Cypress has PSoCs which can operate at 0.5V power supply. I was wondering how you interface these. 0.5V is too low for FETs and bipolar transistors, LEDs and even common diodes. So what ways are here to connect the PSoC to its peripherals? Low-power is also an issue here: it doesn't help that the PSoC is low-power at 0.5V if the interfacing needs 10 times more power.
Electronic – How to interface with ultra-low voltage microcontrollers
I don't know what you mean by "UWB" (use standard or common abbreviations, no I'm not going to look it up, it's your job to explain), but many many micros have 10 bit A/Ds and SPI hardware. Even without the SPI hardware, SPI is simple to do in firmware by controlling the I/O lines directly.
In the Microchip line, there is a wide spectrum that meet these requirements. A low end PIC 16 can be small, cheap, and very low power. A fast dsPIC33 can run up to 40 MIPS but of course will use more power. There are various PIC 18 and PIC 24 in between.
What you need to explain is how fast you need to sample the 10 bit A/D and what the micro needs to do to these 10 bit values before passing them on via SPI.
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You have now added that the A/D sample rate is 500 kHz and that this raw A/D data is to be passed on via SPI. Since the A/D is 10 bits, this is apparently where you got the 5 Mb/s SPI data requirement from.
This is doable, but will require a reasonably high end micro. The limiting factor is the 10 bit A/D at 500 kHz sample rate. That's quite fast for a micro, so that limits the available options. Another thing to consider is that there is more to SPI than just sending the bits. Bytes may need to be transferred in chunks with chip select asserted and de-asserted per chunk. For example, how will this 10 bit data be packed into 8 bit bytes, or will it at all?
The main operating loop of the firmware will be quite simple. You probably set up the A/D to do automatic periodic conversions and interrupt every 2µs with a new value. Now you've got most of 2µs to send it out the SPI. If the device really can just accept a stream of bits, then it might be easier to do the SPI in firmware. Most SPI hardware wants to send 8 or 16 bits at a time. You'd have to buffer bits and send a 16 bit word 5 out of every 8 interrupts. It might be easier to just send 10 bits each interrupt in firmware.
Sending SPI bits in firmware if you only need to control clock and data out is pretty easy. Per bit, you have to:
- Write bit value to data line.
- Raise clock
- Lower clock
It would make sense to unroll this loop with preprocessor logic or something. A PIC 24H can run at up to 40 MIPS, so you have 80 instructions per interrupt. Obviously you can't use 8 instructions to send each bit. If you can do it in 6 it should work. There is some overhead to get into and out of each interrupt, so you might make the whole thing a polling loop waiting for the A/D, but then the processor can't do anything else. I'd probably try to cram this into the A/D interrupt routine using every possible trick so that at least a few forground cycles are left over for background tasks like knowing when to stop, etc.
Check out the Microchip PIC 24H line. I think most if not all have A/Ds that can do 500 kbit/s, and they can all run at least up to 40 MIPS. The new E series is even faster, but I'm not sure how real that is yet.
Yeah, I think Option 2 is your simplest high-side option. Replace Q1 with a BSS138, and you can have a simple all MOSFET solution with discrete parts.
Alternately, if you're OK buying ICs, you can use an IC like the TPS2557 (which is an N-channel load switch with built-in charge pump), or an integrated dual N/P part like the Si3865DDV which basically squeezes the option 2 circuit into a convenient package. These would also take up less space than the discrete solution, and offer some protection features such as current-limiting if you would like. I can also understand the appeal of building something with parts you have lying around.
A N-channel device will have a lower on-resistance than a comparable P-channel device, but it does require a charge pump as you stated.
Finally, even with a MOSFET solution, I would personally keep R2 there and make it 1k or so, in addition to adding a pull-down to your UC enable pin so that when you are in reset, the LEDs stay off. By keeping R2, if you drop a screwdriver or something across the gate of the MOSFET to GND, it limits the current that can flow from the uC pin.
Here's the discrete solution:
simulate this circuit – Schematic created using CircuitLab
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The PSoC CPU does not actually run from 0.5v. Its minimum running voltage is 1.8v. However, the chip also contains a high efficiency boost regulator which works down to 0.5v and can boost that voltage up to the 1.8v that the PSoC requires. The boost converter can supply upto 50mA current, which can be used by the rest of the circuit.