The first step to designing a battery charger is choosing a battery charger IC from the vast field of available solutions. To make an informed decision, a design team must first clearly define the battery parameters (chemistry, cell count, etc.) and the input parameters (solar, USB, etc.). The team must then search for chargers that fit the input and output parameters, comparing numerous data sheets to settle on the best solution. The selection process should allow the team to pick the best solution for the application, until of course, the design parameters change, at which point: back to the data sheets.
What if this step could be skipped altogether? What if a designer could focus on an application solution, treating the battery charger IC as a black box to be filled in with a real IC when the time comes to produce a working solution? At that time, the designer simply reaches to the shelf for a generic battery charger IC, regardless of the essential design parameters. Even if application parameters change (inputs switched out, battery type changed, etc.) the off-the-shelf battery charger IC still fits. No additional data sheet search required.
This problem can be illustrated by looking at two very different battery charger problems:
- Design team A is tasked with designing a battery charger that takes solar panel input and charges a lead-acid battery. The charger must stand alone—no microcontroller here—but should be versatile enough to support a few different solar panel models. They have one week to produce a schematic design.
- Design team B has a more involved charger problem. Their design takes a 5 V USB supply and charges a 1 cell Li-ion battery with 1.3 A to a termination voltage of 4.1 V per cell. Above 47°C, they want to decrease their charge voltage to 4 V per cell at 0.5 A, and above 72°C, they want to charge to stop. The microcontroller in their system needs to know the battery’s voltage, current, temperature, and health. They also have one week to produce a schematic design.
It turns out that both design teams can use the same battery charger IC, and that this device is arguably the best choice available for both applications.
Good Things and Small Packages
he LTC4162 35 V, 3.2 A monolithic buck charger boasts an elegant blend of simplicity and versatility. Capable of operating standalone or with a host controller, the LTC4162 enables solutions from basic to complex. A full-featured I2C telemetry system allows a user to optionally monitor the battery and implement custom charging parameters specific to the battery model. A true maximum power point tracking (MPPT) algorithm allows the charger to operate optimally from any high impedance source, such as a solar panel. The charging algorithm is tailored to the chosen battery chemistry: Li-ion, LiFePO4, or lead-acid.
These features are packed into a 4 mm × 5 mm QFN package with a typical solution size of about 1 cm × 2 cm.
Feel the Power!
Don’t let its small size fool you. Even with integrated switching FETs, the LTC4162 can support over 60 W of charge power. Internal thermal self-monitoring of its die temperature enables the LTC4162 to regulate the charge current such that it never overheats, even in the hottest environments and tiniest enclosures.
The PowerPath™ FETs (INFET and BATFET) ensure that the system load (VOUT) is always powered by the input voltage (VIN) if it is present or by the battery, if VIN is absent. The use of external N-channel FETs allows for low loss paths with no limit to the amount of current that can be passed to the load.
Telemetry and Control
Although the LTC4162 can operate without a host controller, many aspects of charging can be monitored and controlled through the I2C port. An on-chip telemetry system reads system and battery voltages and currents in real time. Various limits and alerts can be set to notify the host controller when a measured value meets a configurable threshold or when a particular charging state is entered. For example, a common design feature may be to enter a low power mode when the battery voltage drops to a certain lower limit. Rather than have a microcontroller continually poll the battery voltage, the LTC4162 can do the monitoring, and inform the host controller when this limit has been reached. At this point, the host can switch off the main load and enter a low power state.
Read More: One-Size-Fits-All Battery Charger