Low cost $ good load regulation buck 2xLiPo->5V@5A

[poorchava]

Hello,

I'm need a buck converter that will convert 6.2-8.4V from 2S LiPo pack to 5V at 0-5A. Key parameters are low complexity, low cost and good load regulation. I have a few options from Texas and Linear, but they are either expensive(Linear), hard to get in my country (new TI chips) or both.

My first shot was LM3475, because it is small and cheap and not actually current limited because of external PMOS. The downside is that it is a hysteretic mode controller, which means that its frequency varies greatly with load and so does the required inductance value.

Second shot is LTC1773 but it's very expensive (~4€) and only available from Farnell.

Can you recommend any particular chip?

[kizzap]

Would it be possible to use a jellybean part with an external transistor? I think a device capable of 5A in a single package might be difficult to get.

-kizzap

[onlooker]

AOZ1014 on ebay, 5 pcs for $6 with free shipping. Though, I don't know if they are any good. I was looking for a replacement.

[poorchava]

Would it be possible to use a jellybean part with an external transistor? I think a device capable of 5A in a single package might be difficult to get.

-kizzap

External switch is absolutely ok. I realize that 5A with integrated switch will be hard to find.

AOZ1014 on ebay, 5 pcs for $6 with free shipping. Though, I don't know if they are any good. I was looking for a replacement.

Wow, that seems really nice. I've never heard or Alpha&Omega Semiconductor before. 38mR internal p-mosfet is really good spec. I mean most of the integreted switch regulators have ~100mR. I will definitely give it a try.
Too bad that there's no DFN version on ebay. It has better power dissipation.

[peter.mitchell]

http://www.ti.com/product/lm2587 they look pretty good but as you said hard to find in PL

[poorchava]

This one is for boost, flyback or forward conversion. There is a similar chip from TI (don't remember the number right now) capable of 5A output, and even available in PL, but on an expensive side (around $7 a piece). My budget for the regulator is around $3 tops (including inductor, catch diode, input and output capacitors and whatever minor passives are needed). Seems like the AOZ1014 fills those requirements, if I use ceramic caps instead of low-ESR electrolytics.

[peter.mitchell]

I'd use AOZ1094 instead of AOZ1014, it is in production.

[poorchava]

I'd use AOZ1094 instead of AOZ1014, it is in production.

And hardly available from ebay or anywhere else. As a matter of fact those two are pin compatible and from quick comparison the only significant difference is lower Rds of internal FET. If I find it that AOZ1014 heats up too much, trips thermal protection or something like that I will consider changing to AOZ1094. On the other hand I can also reduce duty cycle of the load by a little bit (maybe down to 90-95% instead of 100%)

[Psi]

Here's a cheap 3A one  for $2.80
http://www.hobbyking.com/hobbyking/store/__17159__3_3v_3a_ubec_2_5s_lipoly_6_23v_.html

[poorchava]

I've learned about the BEC devices some time ago, but ditched the idea after seeing some tests showing, that 5A BEC would go into thermal shutdown @4.2A with horrendous voltage ripple. Most of those are based on jellybean integrated switch converters like LM2576 or more likely cheap fakes thereof.

Here's the thread on rcgroups: http://www.rcgroups.com/forums/showthread.php?t=1175777