3
\$\begingroup\$

I am building some sort of navigation device for a logisitics project in my company.
The whole thing is going to be battery (6V) powered, so I'm looking for every possible way to avoid losses to heat etc by turning off ports I don't need, stripping peripherals etc..
My lineup so far is a Rapsberry Pi A (40% less consumption than ver. B), a 128 x 64 px touch display that comes with some nice power-down features and an XBee-Pro module, that also has sleep and hibernate modes.

All these devices run on 3.3V. The 5V on the Pi are only used to power the attachable USB devices, so the input to the Pi is regulated to 5V if it is above, then fed to the USBs and again regulated to 3.3V. Both regulations happening with linear regulators afaik, which are not very efficient, aka they just "burn" the undesired amount of V.

Now if I disable the integrated regulators of the Pi and attach my own buck-boost/SEPIC ICs regulator that goes straight and efficient from Vin to my desired 3.3V I can again save a lot of energy.

My problem: I cannot seem to find a suitable chip. The main difficulty is that those I was able to find ususally come in a packaging type that is impossible for human hands to solder.
I am looking for:

  • Vin up to 7V
  • Iout at least 500mA
  • Vout 3.3V
  • buck-boost mode
  • 0.1" pin-out

Any help apprechiated!

schematic

simulate this circuit – Schematic created using CircuitLab

\$\endgroup\$
7
  • \$\begingroup\$ What's the lower limit of Vin and also what do you define as being unable to hand-solder - maybe you should state what package types are acceptable. \$\endgroup\$
    – Andy aka
    Jan 16, 2014 at 13:45
  • \$\begingroup\$ The toughest challenge with the specifications is the 0.1 inch pin pitch. Realistically, it isn't that difficult to hand-solder a 0.05 inch pin pitch SOIC package. SOIC to DIP adapter PCBs make the task easier still. If the OP is open to venturing that far, then options do exist. \$\endgroup\$ Jan 16, 2014 at 14:12
  • \$\begingroup\$ Another suggestion: If a minimum Vin greater than desired output is acceptable, that would widen the choice massively, with boost regulators rather than buck-boost. \$\endgroup\$ Jan 16, 2014 at 14:14
  • \$\begingroup\$ @AnindoGhosh To break it down a bit more: I'll use a 6V depletable source and want to get 3.3V from it as efficient and long as possible. the rest doesn't matter. \$\endgroup\$
    – Mark
    Jan 16, 2014 at 15:08
  • \$\begingroup\$ @Andyaka & Anindo Ghosh: Adapters should be fine, however I'd like to keep the part count to a minimum. \$\endgroup\$
    – Mark
    Jan 16, 2014 at 15:11

1 Answer 1

2
\$\begingroup\$

As OP has not clarified what 6V depletable source is to be used, this answer predicates a battery which has a nominal full charge voltage of 6 Volts, and is operable down to 3 Volts.

As discussed in comments, there are few if any options for an integrated buck-boost device in a 0.1 inch pin pitch DIP form factor. Further, with most manufacturers DIP is rapidly going out of production to be replaced by SMD, so it is inadvisable to use a DIP part for a new design, even if one finds such an option.

A parametric search for SEPIC / buck-boost ICs with the stated criteria, on a major vendor site such as DigiKey yields several options in SOIC packages. These are leaded packages with a 0.05 inch pin pitch, not extremely difficult to hand-solder. One DDPAK-5

Examples:

  • Linear Technology LT1572:

    1.25 Ampere monolithic switching regulator with inbuilt switching MOSFETs, in SOIC-16. Operates from 3 Volts to 30 Volts. Supports most switching topologies including SEPIC.

  • On Semiconductor CS5171:

    1.5 Ampere switching regulator with inbuilt switching MOSFETs, in SOIC-8. Operates from 2.7 Volts to 30 Volts. Similar to above, supports several topologies including SEPIC.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.