The next best power management solution to zero power is nanoPower

-March 14, 2017

With the growth of wearable designs (Experts say CAGR of 18.4% by 2020) and other battery-powered consumer solutions for the IoT, circuit designers are demanding the longest battery life possible from the tiniest board footprint IC. The caveat is they also want more functionality.


When I saw Maxim Integrated’s MAX17222 boost regulator, it got my attention (By the way, there are some excellent application notes in the data sheet for some very practical applications). With a tiny 300nA quiescent current combined with 95% peak efficiency in a 0.88×1.4mm 6-Bump WLP as well as a 2×2mm 6-Pin standard µDFN package, designers have the next-generation power management solution for their ‘flea-powered’ designs. Maxim Integrated is claiming the industry’s lowest IQ and highest peak efficiency. The low quiescent current is helped by a clever design capable of operating at low input voltages via bootstrapping itself and drawing current from the output.

 

The input range of this device is a pretty wide 0.4V to 5.5V with an output swing capability of 1.8V to 5V. An input current limit of 500mA shrinks the solution size by up to 50% compared to similar products and the 95% peak efficiency minimizes the heat dissipation.

 

A true shutdown mode

 

Here is something I like for designers who want to save battery life: a true shutdown mode in which the total system shutdown current is the sum of the ICs total shutdown current plus the current flowing in the external pullup resistor (Figure 1). In this case the IC’s EN pin is connected to an open-drain GPIO of a microcontroller, with a VIN of 1.5V, VOUT of 3V, and a 33 MΩ pullup resistor giving a total system shutdown current of 45.9nA. This True Shutdown feature eliminates the need for an external disconnect switch.

 
Figure 1 In a true shutdown mode, the total system shutdown current is the sum of the ICs total shutdown current plus the current flowing in the external pullup resistor.

I am always wary of shutdown modes, because designers usually need to know how fast the power supply can be restored and many times the result is not acceptable; but this data sheet prominently displays the startup curve with a measured slew rate of 2 mV/us (Figure 2).

 
Figure 2 The startup curve has a measured slew rate of 2 mV/us.

Small board footprint with less external components

Aside from eliminating an external switch to achieve full shutdown to save the battery life, a simple ceramic output filter capacitor is typically all that is needed. A small 2.2 uH inductor will work for most applications. The data sheet has some excellent guidelines for proper selection of these components under any special conditions as well.

Another area that designers will like is the single configuration resistor, RSEL, to set the output voltage instead of the two feedback resistors typically needed in most regulators. More importantly than just saving one board resistor footprint, this single resistor configuration eliminates the wasted current that would be drawn through those feedback resistors which would be an added drain on a battery.

 

Enable transient protection current

Another neat feature of this device is the internal circuitry that protects against accidental shutdown by any transient on the EN pin. Once the IC is started up, the voltage at the input can drop as low as 400 mV and the IC will remain enabled (Battery drain is significantly reduced during standby and shutdown modes to maximize operating time; 0.4V input [with 0.88V startup input] is compatible with low voltage batteries and supercapacitors). The cost here is a slightly higher supply current in the area of 10s of nA. Alternatively, designers can choose other members of this family which do not have this feature to keep the battery drain as low as possible. See the data sheet for more details on this.

 

Lowering your IQ

 

You have to check out this section which gives designers tips on saving battery power and also includes an excellent and humorous video by “Dr. Gilbert Weinstein” on lowering your IQ that’s too funny and is a must-see.

 

This device operates over the -40-degree Celsius to +85-degree Celsius temperature range. The MAX17222ELT+ is available for $1.23 (1000-up, FOB USA) and the MAX17222EVKIT# evaluation kit is available for $34.99. An EE-Sim model is also available. Visit the Maxim integrated website for more details.

Loading comments...

Write a Comment

To comment please Log In

FEATURED RESOURCES