IC overcomes solar cell/battery-chemistry charging conundrum

Milpitas, CA—Solar cell panels offer great potential for alternative, backup, and even primary power, but nearly all such installations need batteries to store their output and provide carry-though during dark periods. And that's the problem: the "load line" characteristics of these panels requires careful management of the panel's power versus current curve, to optimize the output and yield maximum peak output versus lighting conditions. In other words, it's all about Maximum Peak Power Tracking, or MPPT.

The LT3652 IC from Linear Technology Corp aims to greatly simplify the challenge. This device incorporates what the vendor claims is an innovative input voltage regulation loop which extracts the maximum available output power from the panel. It maintains the panel at the input voltage which matches the peak output power point from that panel, and allows the user to program the specific desired peak-power voltage via an external resistor. The input supply loop is designed to allow efficient and optimized charging for poorly regulated sources, such as solar panels, where the input can "collapse" under overcurrent conditions of excessive load draw.

The IC functions as a 2A battery charger with 32-V operating/40-V maximum input voltage, and charges various batteries types including one-to-three Li-ion/polymer cells in series, on- to-four Li-iron phosphate (LiFePO₄) cells, and sealed lead acid (SLA) batteries up to 14.4 V. It includes onboard charge termination with C/10 (C is nominal charging current) or timer control; no external microcontroller is required. .

Operating at a fixed switching frequency of 1 MHz, the float-voltage feedback accuracy for the LT3652 is ±0.5%, with charge-current accuracy of ±5% and C/10 detection accuracy of ±2.5%. At the end of the charge cycle, the IC automatically goes into a low-current standby mode, dropping its supply current to 85 μA. For applications using autonomous charge control, the auto-recharge feature begins a new charging cycle if the battery voltage drops 2.5% below the programmed float voltage—Bill Schweber.

Packaging, pricing, and availability: The LT3652 is packaged in a low-profile, 12-lead DFN package measuring 3×3 mm. It is available immediately; prices begin at $3.05 (1000-piece lots).