5 Ways to Boost your Bluetooth Product's Battery Life

Written by Jared Wolff

If your product is powered by a battery, then battery life is something you inevitably find yourself thinking about. In fact, battery life can often make or break a product. For instance, I can think of a pair of Bluetooth headphones that didn’t quite cut it because of their poor battery life. As a result, they are no longer with us.

So how can your product avoid the trash bin? Follow these five simple design tactics to boost your product’s battery life and save it from the trash. 

1. For severely constrained products, increase the value of your pull-ups/downs

Bluetooth Picture 1

One of the most overlooked pieces of a circuit are the pull-ups and downs attached to both input and outputs of integrated circuits, FETs, etc. When the input or output is the same (or not active), additional current flows through that resistor. But when active, according to Mr. Ohm, the current is flowing proportionally to the size of the resistor. Put simply, the smaller the value, the higher the current, and vice versa.

So, where you can, reduce the size of pull-ups and pull-downs, especially if current will be flowing through them for most of the life of the device.

A few things to remember about this: 

A. Input bias current
Some devices require a certain amount of input current to work properly. Whether it’s an enable pin on a buck or GPIO, there’s usually a minimal amount of bias required to set logic levels correctly.

B.  I2C pull-ups
I2C pull-ups are tricky and do require tuning depending on how many devices you have on your bus. I have found that in low power cases with as little as 3-4 devices you can usually get away with 20k. If you use I2C a lot, then this will save your hide (and your battery life).

C.  RC effect
Finally, the higher the resistance, the slowly your circuits will respond due to the charging or discharging of whatever capacitance (parasitic or not) is connected to the other end of the pull-up/down. Best to be sure and probe the signal with an oscilloscope.

2. Completely remove pull-ups and downs and use push-pull devices

Changing 1K to 1M ohm is one option, but what if that static current is really bugging you?

Remove it all together. 

Bluetooth Picture 2

Some devices use an open-drain architecture, which usually leads to the need for pull-ups. Sometimes chip manufacturers make variants that are push-pull. Push-pull, while for a very short instantaneous amount of time draw higher current, draw nearly nothing in a steady state.

Be aware that this can’t be avoided in some cases. For instance, when pull-ups and pull-downs are used to set the “starting state” of a signal. If it weren’t for a pull-up or pull-down, a Hi-Z input could float at weird voltage levels, causing your input circuitry to go haywire. So, avoid it with a reasonably sized pull-up or pull-down.

3. Choose low Iq circuitry

A third option is to use the filter function on sites like Digikey and Mouser to sort by devices with lower Iq (quiescent current — i.e. minimal current required to operate). In a battery-powered application, you can afford to pay for a better part when it can squeeze out a few more months of operation.

When doing your research in the data-sheets, be sure to validate and verify yourself. Remember, Trust but verify! One way to verify is to measure your system current with an accurate test setup. I’ve used this technique now for several products and I’ve always learned something about my circuit that I otherwise would have not found if I hadn’t look at it from the current draw perspective.

4. Get your micro controllers into sleep as often as possible

Not everything here can be solved with hardware. For example, if you don’t put your micro-controller to sleep, it may draw anywhere from 1mA to 10mA, or more. That’s a surefire guarantee that your device will last a day. (Cue the sad trombone). So, finding a way to batch your operations and quickly go to sleep will save power and extend your battery life!

5. Power it down when not in use

Bluetooth Picture 3

Going a step further, if you truly want to draw the least amount of current while your system is “sleeping”, power it off when it’s not being used. In other words, shut down all the rails that are not needed; even the ones powering a micro-controller.

 Then, in order to power back on, you have a few options:

  1. Low Iq sensor devices that can “wake up” the power supply which, in turn, wakes up the micro-controller.
  2. A real time clock which does the same as above but can be set to trigger an output pin with an alarm. This method sips current (I’m talking about nano-amps here) and is the preferred method, especially if you are taking environmental measurements on a regular basis.

 

Conclusion

If you can master the five techniques above, you can master getting your product as low power as possible. That means less customer complaints and more up-time. What’s not to love about that?

About The Author

Jared Wolff

Jared Wolff

Veteran Product Leader And Wearer of Many Hats, Circuit Dojo

Helping companies navigate the potential pitfalls, put in processes that save cost and time and leads the product design process with not only next month in mind but next year and beyond. And, of course, ship products!

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