SparkFun Forums

[UNTEngineer]

I've been coming across load management devices lately for auto switching between a USB power source and a voltage source. How would I go about implementing these devices, and what sort of applications require them vs others. Im working on a project that has both USB and DC voltage inputs, but probably wont have them connected at the same time. However, if I need to troubleshoot while it is in the field, it would be nice to be able to implement that. :think: I'll be using an Atmel 32u4. The load management device Im referring to is the FPF2123.

[UNTEngineer]

bump?

[langwadt]

if you can live with the loss of a diode voltage you can just put a diode in series with each supply, the active switching is for when you cannot live with the voltage or power loss over a diode so it uses fets instead

[UNTEngineer]

if you can live with the loss of a diode voltage you can just put a diode in series with each supply, the active switching is for when you cannot live with the voltage or power loss over a diode so it uses fets instead

But how do I implement that schematic wise. Im trying to understand how it is working (and what its doing).

[Mee_n_Mac]

Im trying to understand how it is working (and what its doing).

By "it" do you mean a FPF2123 ? Is so realize it doesn't switch between 2 supplies, it switches a single supply on/off (to a load) based upon either a logic command or a current overdraw condition (ie - a short circuit). I suppose you could wire the outputs of 2 of them together if you could guarantee that the on/off commands to both would never overlap (both on at the same time). But in your OP you said ...

has both USB and DC voltage inputs, but probably wont have them connected at the same time

... which makes me less sanguine about this approach. I thought Maxim (?) made some ICs that were specifically for switching btw 2 supplies, automagically deciding which to use (thus eliminating the logic needed to use two FPF2123's).

[UNTEngineer]

By "it" do you mean a FPF2123 ?

Yea I meant the FPF2123. You say it is used to switch between loads for one power supply. What sort of situation requires switching between two loads, instead of just having two sources?

... which makes me less sanguine about this approach. I thought Maxim (?) made some ICs that were specifically for switching btw 2 supplies, automagically deciding which to use (thus eliminating the logic needed to use two FPF2123's).

Could you recommend one for switching between 2 supplies?

[Mee_n_Mac]

By "it" do you mean a FPF2123 ?

Yea I meant the FPF2123. You say it is used to switch between loads for one power supply. What sort of situation requires switching between two loads, instead of just having two sources?

No, it switches a single load, to be either connected to the supply or disconnected, like a simple SPST switch. It does this upon (logic level) command or when it senses a short circuit (or current over some threshold). It limits the current supplied to some max amount during the switchover time and variations of the IC can automagically check to see if the short is gone and if so, re-apply power.

I imagine you could use 2 of them and connect a single load to 2 separate supplies, though only to one supply at any one time, by connecting each IC's output to each other and the load. The IC is basically a FET used as a high side switch with the "smarts" to connect/disconnect as already described.

... which makes me less sanguine about this approach. I thought Maxim (?) made some ICs that were specifically for switching btw 2 supplies, automagically deciding which to use (thus eliminating the logic needed to use two FPF2123's).

Could you recommend one for switching between 2 supplies?

I'm not familiar with the numerous products that do this nor do I have any idea what your requirements are. But Maxim (and other vendors) have a selection guide / automated helper that can winnow down the choices to a few for you. IIRC there was also mention of a USB/battery power switching IC in this forum, perhaps a search will find that thread.

[UNTEngineer]

Hmm, ok. Thanks.