Page 17 - Issue 4 2023

ELECTRONICS

How to prototype a power bank charger

without building any dedicated hardware

By Diarmuid Carey, Staff Applications Engineer, Central Applications Analog Devices

solar or to charge via a DC input from a standard 12 V AC-to-
Question: DC wall wart was included. The outputs included some basic
Can you prototype a power bank charger application without USB-A charging ports (two in total), producing 5 V for use with
building any dedicated hardware? mobile phones and a range of USB-powered electronics.

Answer: Hardware Selection
The short answer to this question is yes, and, as this question Power Source Selection – LTC4416
has been asked many times over the years, this article was In this example, the design will support two input power sources
written to explore the topic in further detail; reviewing the (a solar panel and an AC-to-DC wall wart, which is just a simple
process involved in developing an application using existing AC-to-DC power supply). For this reason, a clever device called
evaluation boards, discuss the challenges encountered, a power path prioritiser is required not only to intelligently
and outline recommendations for further revisions and switch between the available sources depending on which was
improvements.
available, but also to manage the situation where they both
were available by assigning priority to one source or the other. A
Ideally, any power supply design should start with some simple version of this implementation can be achieved by using
basic proof of concept tests, which often involve testing an some simple diodes – commonly connecting the two cathodes
existing demo board. This demo simply takes this preexisting of the diodes and connecting the anodes to their respective
step (of testing single rails on the demo hardware) and sources. Unfortunately, this particular configuration is lossy due
expands on it to produce a working system using demo to the diode drop inherent in a typical diode (approximately 0.6
hardware. Furthermore, as this demo was needed within a V), but it also doesn’t allow for any clever selection criteria to
relatively short time frame, the typical development process be implemented, for example, priority selection. It simply allows
of design, layout, build, assemble and test (plus any design the higher potential input to pass through.
iteration) was not possible, so the system was prototyped in Here LTC4416 comes into play – it not only replaces the
its entirety using nothing but readily available hardware.
lossy diodes with PFETs, which are far more efficient, but also
allows for priority to be assigned. In this particular application,
Application priority will always be assigned to the wall wart. This allows
To answer the question posed at the beginning of this article, the design to take advantage of the available power (and
it was necessary to choose a high-level application as a starting higher current) when it is available. This device is exceptionally
point to prove this was possible. This led to the power bank flexible, with many operational modes possible depending on
charging application being selected as a proof of concept. the design requirements. Table 1 (sourced from the LTC4416
As power management is a prerequisite for every electronic data sheet) displays the modes of operation.
project, any other application could have been selected.
A power bank charger is a common enough application, E1 E2 Operation Mode IG(OFF)1 IG(OFF)2
which most consumers have encountered and used – for 1 0 Load sharing Enabled Enabled
example, many travelers carry one to ensure their phone
remains charged over a long journey. A power bank is 1 Sense V1 is less than V2 Enabled
essentially a battery pack (capacity varies depending on the Sense 0 V1 is greater than V2 Enabled
price and range required), with one or more USB-A ports as Channel 1 disabled Disabled

well as a USB-C input port to charge it. It is possible of course to 0 X Do not use
layer additional complexity on top of this basic functionality – X 1 Channel 2 disabled Disabled
for example, the addition of a wireless charging pad or an input Do not use
to allow solar charging of the bank for outdoor enthusiasts. 0 1 Both channels disabled Disabled Disabled
For this application, the option to charge the battery via Table 1. Modes of Operation from the LTC4416 Data Sheet

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