LT8491

The DC2703A-A-KIT contains the DC2703A (LT8491demo board) and DC1613A (USB-to-I²C controller). Together they provide a high performance buck-boost battery charger converter with an I²C interface. The LT8491 implements a maximum power point tracking (MPPT) function and flexible charging profiles, suitable for most battery types such as flooded and sealed lead acid batteries and Li-Ion batteries. A Microsoft Windows-Based GUI (Graphical User Interface) application called “simpleLT8491” is provided which can be downloaded here.

The DC2703A-A-KIT demo board is configured for 17V to 54V input voltage range and the power source can be a solar panel with 36 to 72 cells (up to 200W) or a DC voltage source. The LT8491 converter can operate from input voltages above, below or equal to the battery voltage. Two input connectors are provided. An ideal diode controller LTC4359 protects the DC power supply output from being back fed from the solar panel. This allows, for example, a 24VDC supply to be plugged in while a solar panel with higher voltage is being used to power the circuit. The DC2703A-A-KIT demo board output is set up for charging a 12V SLA battery with up to 16.6A charge current. The DC2703A-A-KIT demo board can be modified to support much higher output voltage, with modifications including higher voltage rating output side MOSFETs and capacitors.

The LT8491 includes a slave I²C compatible interface for digital control of the charger settings and digital readouts of charger telemetry and status. A Microsoft Windows- Based GUI (Graphical User Interface) application is provided for this demo board, which makes it very easy to read charger telemetry and status data, as well as the ability to change the charging algorithm by writing to the appropriate configuration registers. The LT8491 EEPROM on the DC2703A-A-KIT demo board is programmed with the onboard resistor values to accurately read charger telemetry and status registers data.

On-chip logic provides automatic true power point tracking (MPPT) for solar powered applications. The MPPT function not only continuously tracks the maximum power point, but also periodically sweeps the input panel voltage in order to select the correct maximum on the power curve. In doing so, an increase in power harvested from the panel during partial shade conditions is possible when multiple peaks occur on the power curve. During periods of low light, a low power mode allows the charger to deliver a small charge current even if there is not enough light for the MPPT function to operate.

An RJ25 modular jack can be used to connect an external NTC temperature sensor mounted at the battery. This allows temperature compensation of the charge voltage, which is important for lead acid batteries. The same connector can be used for remote sensing of battery voltage, to compensate for voltage drops in long battery cables. The onboard LED displays the charge state.

The LT8491 data sheet gives a complete description of the device, operation and application information. The data sheet must be read in conjunction with this demo manual for DC2703A-A-KIT. The LT8491EUKJ is assembled in a 64-lead (7mm × 11mm) plastic QFN package with a thermal pad underneath the chip. Proper board layout is essential for maximum thermal performance.