L6924U
Application information: monitoring and protection
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.
Figure 16. Power dissipation in both linear and quasi pulse modes with thermal loop
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
connected to VREF. When the voltage on the TH pin exceeds the minimum or maximum
voltage threshold (internal window comparator), the device stops the charge process, and
indicates a fault condition through the status pin.
Doc ID 14716 Rev 2
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