3 Nimh powering 3.3V and 5V rail

Jeferson Pehls

Other Parts Discussed in Thread: TPS63000, TPS63030, TPS63020, TPS63060, TPS63010, TPS61040, LM2735, LM3668

Hello Sirs.
I working on development of three products who will be powered by batteries.
I'm thinking to use 3x 1,2V NiMh batteries in series. Considering them connected in series, the voltage of the system will be around 3V (when the batteries are almost fully discharged) and around 4.2V (when they are fully charged). I will also need to use these power supplies on USB ports (range 4.75 to 5.25V).

So my actual input range will be 3V to 5.25V. 
Considering some tolerances, I will need two kinds of power supplies:

A) Input range: 2,8V to 5,5V. Output: Fixed at 3,3V (capability of 400mA or more)
B) Input range: 2,8V to 5,5V. Output: Fixed at 5V (capability of 400mA or more)

Which IC is recommended to meet these requirements, some ideas? I think some Bulk step-up\step-down converters may do this job fine. 
Remembering that input voltage is adjustable (2,8 to 5,5V) and not a fixed voltage.

I checked LM2735's datasheet from National but I continue thinking that input voltage must be stable to obtain a stable output voltage with this IC and thats not the objective of this power supplies.

An easy-to-find IC would be great. From National, Fairchild, Microchip, Texas etc.
Im looking for an IC in SMT package, like SOT23, SOT223 or something similar.

Somebody suggest ICs for this purpose?

over 13 years ago

0 Chris Glaser over 13 years ago

TI__Guru**** 150620 points

Our TPS630xx series is perfect for your application. These converters buck or boost to keep the output regulated. There are different package options and output currents in the family. TPS63000, TPS63010, TPS63020, TPS63030, and TPS63060.

0 Jeferson Pehls over 13 years ago in reply to Chris Glaser

Expert 1170 points

Hello.

Thanks for the help.

And about the TPS61040 controller? It fits my requirements?

The input voltage range will be 2,8 to 5,5V in both cases (A and B). 
One power supply with 3,3V output and the other with 5V output.

My fear is that sometimes the input will be lower than the output and sometimes higher than the output voltage.

As I understand, in a boost converter the output is higher than input.

But in my case, the input voltage may be lower or higher than the output.

Example: The input is at 5V and the output must be 3.3V. 
Acording to the datasheet, the output voltage must the higher than VIN. There is an error here


I found this IC (TPS61040) available to buy near where I am now.

Is there some App notes for this IC or online apps to calculate the values of components?

I don't have so much time now to deeply study how this controller works.

Are you familiar with this IC?

0 Chris Glaser over 13 years ago in reply to Jeferson Pehls

TI__Guru**** 150620 points

The TPS61040 is a boost converter. It can only regulate Vout to be greater than Vin. For your Vin and Vout requirements, you need to use a TPS63xxx device.

The datasheet contains the necessary information to complete a design with these integrated parts. You must read the datasheet. I also recommend ordering the EVM for the device to test it out. Then, you can download its gerbers from the EVM product page and copy those exactly into your design. This is the simplest and surest way to get a working design the first time.

0 Giuseppe Pinto over 13 years ago

TI__Expert 3950 points

Hello,

The LM2735 should work just fine if used in a SEPIC configuration.

You can take a look at the LM3668 (integrated Single Inductor non inverting Buck-Boost) in 12pin LLP

Regards,

Giuseppe

0 Jeferson Pehls over 13 years ago in reply to Giuseppe Pinto

Expert 1170 points

Hi. Thanks for the help until now.

Here is my schematic, I´m gonna make another PSU with 3.5V output and the same input range using the same configuration, just changing the FB resistors.

I will put capacitor C5 pins very close to VIN an PWRPAD (the pad under the IC), and capacitor C6 very close to VOUT and PWRPAD pins of tps63000.

Some recommendations?

OBS: I don´t want to use constant voltage regulator: TPS63001 or TPS63002

Some recomendations?

0 Chris Glaser over 13 years ago in reply to Jeferson Pehls

TI__Guru**** 150620 points

I recommend you just order the EVM, http://www.ti.com/tool/tps63000evm-148, and then copy its layout exactly.

Make sure the IC is configured within the recommended range in the datasheet.

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3 Nimh powering 3.3V and 5V rail