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

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 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. ADI 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, we have 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.

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

Figure 1. Simplified Diagram of LTC4000 Battery Management System.

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 Analog Devices 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.

IC Topology Input Voltage Range  Output Voltage /Current Battery
LTC3789 Buck-Boost 6-36V 14.4V/5A 4S LiFePO4
LTC3789 Buck-Boost 9-30V 16.8V/5A 4S Li-Ion
LTC3851A Buck 5-38V ~4V/12A 4V Lead Acid
LT3845 Buck 15-60V 10.8V/10A 3S LiFePO4
LT3845 Buck 36-48V 29.4V/2A 7S Li-Ion
LT3845 Buck 5-38V ~4V/12A 4V Lead Acid
LTC3786 Boost 6-21V 21V/5A 5S Li-Ion
LTC3787 Boost 12-21V ~30V/10A 24V Lead Acid
LTC3862 Boost 10-20V ~55V/4A 48V Lead Acid
LTC3862 Boost 19-24V 42.5V/53.5V/5A 11/13S Li-Ion
LTC1952-1 Forward 36-75V 53.5V/1.4A 15S LiFePO4
LTC3805 Flyback 18-72V 4.2A/2A 1S Li-Ion
NCP1230A Flyback 110-220Vac 14.4V/0.3A 4S LiFePO4

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 inputsupply 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.

Figure 3. Typical Application: LTC4000-1 Solar Panel Input 6V to 36VIN to 14.4V at 4.5A Buck-Boost 4-cell LiFePO4 Charger.

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.



Trevor Barcelo

Trevor Barcelo has over 15 years of experience at Linear Technology as an analog IC design engineer, design manager and product line manager. He began his career at Linear Technology’s headquarters in Milpitas, CA by designing the LTC1733 Lithium-ion battery charger. After moving to the company’s Boston Design Center, he continued designing battery chargers and USB power managers including the LTC4053LTC4066 and LTC4089. He holds five patents related to power management. He currently defines battery charging, power management and wireless power products while managing a team of design engineers developing those products.

Trevor received an M.S. in Electrical Engineering from Stanford University and a B.A. in Physics from Harvard University.