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What to Do If You Can’t Find a Battery Charger IC for Your Application

Trevor Barcelo - Product Line Manager - Battery Management Jun 25th 2013

Batteries are used in an application space that is broad and varied.  To accommodate such a wide range of products, battery charger IC manufacturers have an almost equally broad and varied line-up of solutions. However, it is virtually impossible for companies, such as Linear Technology, to predict all of the clever ways engineers will use batteries and power supplies. So what do you do if you can’t find the battery charger IC for your application?

The first step involves outlining your power requirements.  What is the input voltage and current capability of the power supply (or power supplies)? What is the voltage range and capacity of the battery pack?  What are the power requirements of the application? What voltage range is suitable for the application?

Chances are that if you have a 5V input supply and a single-cell Li-ion battery you didn’t make it past the title.  Linear Technology alone has dozens of parts for that application.  More likely you are still reading because the answers to the previous questions indicate that your input supply can be above or below the battery stack voltage.  Or, perhaps, you need more than 10A of charge current.  Maybe you want to use AC mains for your input supply or your battery voltage is greater than 20 or 30V.  There are few, if any, standalone battery charger or power management ICs that can meet these requirements.

However, Linear Technology has one that might help – the LTC4000.  The LTC4000 is not a standalone battery charger or power management IC.  Instead, think of it as the power management brains in a battery-powered system.  It relies on a second IC for brawn.

What to Do If You Can’t Find a Battery Charger IC for Your Application Figure 1. Simplified Diagram of LTC4000 Battery Management System

Figure 1 is a very simplified advertisement diagram for the LTC4000, but it does a good job of showing the basic system. Many of the features and functions are missing from this diagram, but it highlights several key LTC4000 concepts:

  1. Wide input voltage range (3 – 60V) … though essentially unlimited if one feature is not required
  2. Wide output / battery voltage range (up to 60V)
  3. High current capability (essentially unlimited)
  4. Power conversion topology independent

These four concepts make the LTC4000 a suitable candidate for many battery powered systems that do not have a standalone IC solution.

The applications team at Linear Technology has built and tested many different configurations of LTC4000 (see Figure 2).  In fact, we have yet to test a configuration that we couldn’t make work.  Sometimes it takes a little bit of creativity to get the proper control function, but the variety of possible solutions is virtually unlimited.

What to Do If You Can’t Find a Battery Charger IC for Your Application Figure 2. LTC4000 Applications that have been built and tested

I’m not going to spend time going over the details of the LTC4000 battery charger features and functions here. That is best done by checking out the datasheet. But to give you a little preview – the LTC4000 provides the precise control of input current, charge current and battery voltage demanded by modern battery applications. To ensure that power from the available input supply flows to the appropriate load, the LTC4000 features an intelligent PowerPath topology that preferentially provides power to the system load when input power is limited. The LTC4000 controls external PFETs to provide low loss reverse current protection, low loss charging and discharging of the battery and instant-on operation to ensure system power is available at plug-in even with a dead or deeply discharged battery. A version of the LTC4000 (LTC4000-1) replaces input current control with input voltage control. This can be useful to control power limited sources such as solar panels. Figure 3 shows a typical application schematic, using the LTC4000-1 in conjunction with the LTC3789 buck-boost controller.

What’s the feature that limits input voltage to 60V?  Well, one of the several parameters that the LTC4000 can control is average input current.  However, this feature requires a sense resistor connected in series with the primary input supply. The maximum voltage rating of the pins that touch the sense resistor (CLN and IN) is 60V.  If average input current limit is not required, then the LTC4000 can be biased from a resistor, zener diode and capacitor, allowing the primary input voltage to go up without bound.  In another article, I’ll discuss some application specific details about the LTC4000 including this one.

So what do you do if you can’t find a battery charger IC for your application? I recommend that you give the LTC4000 serious consideration.  Its wide input and output voltage range along with its unique topology can turn just about any DC/DC (or AC/DC) converter into a full-featured battery power management system.

What to Do If You Can’t Find a Battery Charger IC for Your Application Figure 3. Typical Application: LTC4000-1 Solar Panel Input 6V to 36VIN to 14.4V at 4.5A Buck-Boost 4-cell LiFePO4 Charger