L6924U

Application information: monitoring and protection

Doc ID 14716 Rev 2

23/37

8

Application information: monitoring and protection

The L6924U uses a VFQFPN (3 x 3 mm) 16-pin package with an exposed pad that allows

the user to have a compact application and good thermal behavior at the same time. The

L6924U has a low thermal resistance because of the exposed pad (approximately

75 °C/W, depending on the board characteristics). Moreover, a built-in thermal protection

feature prevents the L6924U from having thermal issues typically present in a linear charger.

Thermal control is implemented with a thermal loop that reduces the charge current

automatically when the junction temperature reaches approximately 120 °C. This avoids

further temperature rise and keeps the junction temperature constant. This simplifies the

thermal design of the application as well as protects the device against over-temperature

damage.

Figure 16

shows how the thermal loop acts (dotted lines), when the junction temperature

reaches 120 °C.

8.1

NTC thermistor

The device allows designers to monitor the battery temperature by measuring the voltage

across an NTC or PTC resistor. Li-Ion batteries have a narrow range of operating

temperature, usually from 0 °C to 50 °C. This window is programmable by an external

divider which is comprised of an NTC thermistor connected to GND and a resistor

voltage threshold (internal window comparator), the device stops the charge process, and

indicates a fault condition through the status pin.

Figure 16.

Power dissipation in both linear and quasi pulse modes with thermal loop