Datasheet

L6924D Application information: monitoring and protection
Doc ID 11908 Rev 9 23/38
8 Application information: monitoring and protection
The L6924D uses a VFQFPN 3 mm 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 L6924D 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 L6924D 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.
The Figure 18 shows how the thermal loop acts (with the 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 connected to
V
REF
. 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.
Figure 18. Power dissipation both linear and quasi pulse mode with thermal loop