BBB startup current

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41

You know that you are nit picking right now. The requirements are clear, 5V2A. Test any of these supplies, and see what happens to the supply when you try to take 3A, it won’t and it will current limit at close to 2A. For UL requirements, they all have short circuit protection, which is a safety requirement. Most of these supplies are based on switchmode technologies and hence naturally current limit. This is just common sense, and so why do you expect Gerald to specify every detail. The documentation he compiled is very detailed so I would cut him some slack here.

Here is the recommended power supplies:

http://elinux.org/Beagleboard:BeagleBone_Black_Accessories#Power_Supplies

Here is what is described on the BeagleBoard FAQ

What power peripherals are required/desirable?
  • There are several ways to power a Beagle. The option exists to feed the on-board regulators through either the 5V barrel connector input or USB input. When powered up over USB, the regulators are somewhat limited in what they can supply the system. Power over USB is sufficient as long as the software and system running perform some management to keep it under the USB current limit threshold. For simplicity and maximum capability, powering over the 5V barrel connector is typically recommended.
  • The power adapter is required to provide 5V over a 5.5mm outer diameter and 2.1mm inner diameter barrel connector (a barrel connector length of 9.5mm is more than sufficient). The recommended supply current is at least 1.2A (or 6W), but at least 2A (or 10W) is recommended if you are going to connect up anything over the USB. The actual power consumption will vary greatly with changes on the USB load.

Regards,
John

42

You need to think through the complete problem. Sure you can move the 100uF capacitor to the other side of TPS2051, but you still need a bulk capacitor on the IN side because of HDMI and VIO requirements. The peak current is based on the capacitor ESR and not the size of the capacitor. The size of the capacitor affects the duration of the peak current. So, given that you still need a bulk capacitor on the TPS2051 IN side, you have achieved little by moving some of capacitance to the TPS2051 OUT side. Also, cost of component is only one part of the total cost. Carrying additional inventory, cost of placement, engineering changes, testing, managing another version, can sometimes be far higher than the cost of the component. Anyway, even doing what you asked for will do little to reduce the peak current, so why go through the exercise. Doesn’t make sense to me.

Regards,
John