Balancing is achieved by absorbing charge from higher-voltage batteries and transferring this charge to lower-voltage batteries, ensuring all batteries have the same charge level. This charge transfer is accomplished using a smaller-capacity battery that is sequentially connected through the batteries in the stack. This battery not only transfers charge but also adds its energy to the total energy in the stack, thus increasing its capacity. The chip incorporates the sequencing and control circuitry for the external high-voltage NFETs, voltage monitoring, and protection. The LTC3305 is designed to operate autonomously and does not require a microprocessor or other control circuitry. With the LTC3305, a battery in the stack can be replaced and quickly balanced with the remaining batteries. The LTC3305 is ideal for applications such as telecommunications backup power systems, battery-powered home backup power systems, electric vehicles, and industrial lighting systems.
The LTC3305 uses an auxiliary battery storage cell to transfer charge to or from each battery in the stack. A mode pin offers two operating modes: timed mode and continuous mode. In timed mode, once the balancing operation is complete, the LTC3305 enters a low-power state for a programmed time and then periodically rebalances the batteries. In continuous mode, balancing continues even after the batteries have reached their programmed termination voltage. Additionally, multiple devices can be stacked to balance higher-voltage battery packs in series.
The LTC3305 is supplied in a low-profile (0.75 mm) 38-pin thermally enhanced TSSOP package
. The E and I versions operate within a junction temperature range of -40°C to 125°C.
Key features of the LTC3305
: • A single IC balances up to four 12V lead-acid batteries in series
• NFET-based design
• Stackable for balancing higher voltage battery packs in series
• Standalone operation requires no external microprocessor or control circuitry
• Balancing current is limited by an external PTC thermistor
• Continuous and timed modes
• Programmable undervoltage and overvoltage fault thresholds
• Programmable termination time and termination voltage
• Thermally enhanced 38-pin TSSOP package
