I'm working on digesting the data sheet for the Texas Instruments bq34z100-g1 fuel gauge IC. I'm looking to use this chip with a 2 cell lithium polymer battery pack. If using a multi cell pack the data sheet recommends using the following voltage regulator setup. I'm assuming it's low power but i'm not sure how. I've never seen this setup before. What makes it special.


simulate this circuit – Schematic created using CircuitLab

  • 4
    \$\begingroup\$ Its nothing special, on the contrary, its one of the simplest one can do, and the datasheet explains that the chip has its own regulator built in and that this is just a prereg \$\endgroup\$
    – PlasmaHH
    Oct 30, 2015 at 22:47
  • \$\begingroup\$ What makes you think it is special? \$\endgroup\$
    – user16222
    Oct 30, 2015 at 23:08
  • \$\begingroup\$ It's special if you want it to be special. \$\endgroup\$
    – Andy aka
    Oct 30, 2015 at 23:26

1 Answer 1


It's just a bog-standard series-pass linear reg with with a FET instead of a BJT.

As @PlasmaHH notes, it is often used a pre-regulator in more sophisticate setups. It allows you drop some voltage (and thus power/heat) on an external element. Doing this also lets you extend the voltage input range of your more expensive IC regulator. TI has a separate appnote in which they suggest this.

enter image description here

This prereg idea (even with BJTs) not at all an uncommon. Cordless phones do this a lot for instance because they also use the [higher] pre-regulated voltage directly for a few components and they also derive a lower stable voltage for most of the digital parts. So in those setups it serves a double function (more bang for the buck).


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.