Charge Pump reccomendation

[Krumlink]

As I believe and the other pros on this forum would suggest, they would say to google it. Well when it comes to a possibly costly purchase of the following, I always seek advice from the members here.

Basically what I am ranting on is, that I am looking for a charge pump that is ideal to power 500ma at 5VDC, with an input of between 5.5VDC and 3VDC. I am using a 4 AA rechargeable battery pack, so the ideal max voltage is 4.8VDC with drops around to 4.0VDC I am guessing. I know that MAXIM makes some nice charge pumps, but I do not want to guess as to what to purchase. I have nearly no room for batteries, as the lower deck is already crowded with wires and switches. The only room where there would be a 9VDC battery, is on top where it will throw off its already ideal CoG. So if anybody knows of a great DC-DC converter capable of 500ma max at 5VDc with an input anywhere from 5.5VDC to 3VDC, let me know.

Thanks (to see the updated pictures of ARES see the robotics thread).

 

[Papabravo]

Charge pumps, aka DC-DC converters without inductors, are for low currents only, like say 50 mA. Since the design of a DC-DC converter is probably beyond your skill and equipment level, I'd recommend the purchase of one.

The trouble with using them in a robotics application is the performance under a step load transient. What does that mean? Well if the load is drawing 50 mA and at the closing of a switch the load needs to draw 500 mA then the DC-DC converter may collapse (voltage goes to a low value) before it is able to supply that current. We refer to this as the the supply going to it's knees and not bothering to stop there! To prevent this from happening you need to choose the magnetics with great care.

 

[Mikebits]

Take a look at the max608
https://www.electro-tech-online.com/custompdfs/2008/08/MAX608.pdf

Maybe?

 

[Krumlink]

Mike: Looks like it is 87% efficient at 4VDC in 5VDC out and 500ma. Perfect, and it also has a sample preset 5VDC output schematic. Thanks a lot.

 

[Krumlink]

And purchased. Just what the doctor ordered

 

[Mikebits]

Glad it will work for ya Just take care on inductor selection. See pp 8-9 of data sheet.

 

[Krumlink]

So I use a 50milliohm resistor to get max current at 4.8VDC as Rsense?

 

[Mikebits]

It appears so, not much of a resistor is it. You can get .05 ohm resistors from digikey.

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=607HR050E-ND

 

[Krumlink]

Heh I could just wind up a few inches of wire

 

[Mikebits]

You just might, but I doubt you would have a meter that reads to that accuracy to verify the part. I would just order one to be safe

 

[Roff]

Did you select your inductor from the recommended list in Table 1 of the datasheet (which doesn't seem to be labeled)?

 

[Mikebits]

This looks like website for recommended inductor RCH 855.
https://www.sumida.com/

 

[Mikebits]

Ugh, I tried to link to the data sheet but did not work so I am attaching the data sheet. Can be found on above mentioned website.

 

[Krumlink]

Do you happen to know off hand if thats on digikey or newark?

 

[Mikebits]

Digi-key has this part which may be a substitute.
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=RL855-220K-ND

 

[Hero999]

Heh I could just wind up a few inches of wire

That's a bad idea because that would make more of an inductor than a resistor which could interfere with the operation of the circuit.

 

[Papabravo]

When you get this built you will want to see how it performs under the aforementioned step load transient. Don't be surprised if it falls short of your expectations, this is not uncommon for application circuits from datasheets. You will need a scope to see it however.