Input power spec, auto?

Products Support DragonBoard410c
#1

I was initially thinking of adding some input power filters, but in looking at the bottom of this board, there are a couple of inductors at L13 and L14. Given that the input power spec on this board is 8-18 V, and given those inductors, would it be safe/sensible to power it straight off the noisy power supplied by a CAR (which produces a voltage well within the specified range)?

I’m thinking mainly in terms of alternator hum, and voltage bumps and dips caused by variable loads being switched on and off. It shouldn’t ever surge above 18 volts.

#2

Hi doitright:

The 410c board was designed to run from noisy supplies. Unlike competitor boards 410c doesn’t need a clean 5V supply, it has been designed to run off battery systems (example 7.2V LiPO, 9.6V LiPo, 12V lead-acid, 14.4V Li, etc.). This is ideal for portable applications (automobiles, quadcopters, robots, etc.). The two large inductors you see on the bottom of the board are for the buck-regulators, they take the input voltage and step it down to 5V, and 3.7V. The 96Boards requirement is 8-18V, the 410c board exceeds the requirement and can operate as low as 6.5V.

A ‘normal’ car battery is about 12V when the engine is not running, 13.8V when the battery is charging, and 14.4V when the battery is fully charged. Add to this a potential 10% error in the alternator regulator and you find the max ‘normal’ voltage is about 15.8V. 410c is fine with this voltage. When connecting to the car battery ensure you have the polarity correct, the 410c will not respond well to -12V. The 410c is not protected against reverse polarity power supplies.

There are a few things you need to worry about when connecting the board to a car 12V, 1) the voltage dip when cranking the starter, if the voltage drops below 6.5V the 410c, may reset. 2) a cold weather battery boost. At -40 degrees C, many auto-club tow-trucks will connect two batteries in series (24V) to ensure the car will crank. The 410c will likely fail with 24V. 3) the tow truck driver connecting the boost battery backwards (-12V or possibly -24V).

The final thing you should note, if there is a mezzanine board connected to the 410c, AND the mezzanine board uses SYS_DCIN from the low-speed connector, check that the mezzanine board can operate over a wide range.

Full Disclosure: I am an employee of Qualcomm Canada. Any opinions expressed in this or any other post may not reflect the opinions of my employer.

#3

Haha, for my own use, I would never let a tow truck flunkie touch my vehicle (I know too many tow monkeys to trust them). But I will definitely keep all that in mind if setting things up for others.

FWIW: “boost” battery chargers would also over-volt the system when in boost mode, which I realize now since you’ve got me thinking along those lines.

I’m not too worried about low voltage resets, just damaging things. And actually, if it drops to 6.5 or lower when cranking, then the charge is too low to crank the engine anyway. 8 volts while cranking is pretty much the cutoff. My current head unit (kenwood piece of junk) resets when the voltage drops below 10, but since the thing actually turns on with the accessory power signal (which turns off when cranking), it isn’t much of an issue. Happens occasionally while working the snow plow lift pump.

Thank you!

#4

This looks like a reasonable option;

Well… that isn’t going to be happening until at least october. Can’t find anyone willing to ship an envelope of 5 of those for less than an extra $40 shipping charge, so I’ll have to order it for my next trip to the US.