Power Electronics / Power Management


Tiny lithium-ion battery charger

19 August 2009 Power Electronics / Power Management

The new SC824 from Semtech is a linear, triple mode, single-cell lithium-ion battery charger in a 10-lead 2 x 2 mm MLPD package for handheld devices.

The device has 30 V input voltage protection with 9,6 V maximum input over-voltage protection (OVP) threshold. The 30 V input rating protects portable systems against hot plug overshoots and faulty charging adapters. Under-voltage lock out (UVLO) is lowered to 2,85 V so the device is compatible with voltage or current-limited adapters. When charging from USB, a proprietary under-voltage limiting feature reduces the charge current as needed to prevent VBUS collapsing below 4,5 V in case of a weak host or hub.

Compared to previous devices in the SC81x/SC82x family, the SC824 provides additional features including an NTC thermistor interface, multistage timer and an extra indicator flag. The NTC is used to disable charging when the battery temperature rises above or falls below predetermined thresholds. The NTC interface may also enable or disable LDO mode when the battery is disconnected. The optional programmable multistage charge timer protects against a faulty battery, or terminates charging on timeout if the system load is too high to terminate charging on current. Two flags indicate valid input voltage, charger status and faults.

The SC824 incorporates a lithium-ion charging algorithm with multiple regulation loops of constant current, constant voltage and constant die junction temperature. A tri-level logic input selects from three modes of charging: adapter mode, USB low power mode and USB high power mode. Additional charging functions include reverse current blocking, pre-qualification of a low-voltage battery, soft-start to reduce the burden on wall adapters with poor transient response, optional float charging or top-off charging with termination, auto- or forced-recharging and open/short-circuit protection.



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