BQ24080-Q1 Datasheet, PDF (19/28 Pages) Texas Instruments – Li-Ion and Li-Pol Automotive Charger

www.ti.com
bq24080-Q1, bq24081-Q1
SLUSCB6 – MAY 2015
11.3 Thermal Considerations
The bq24080-Q1 and bq24081-Q1 are packaged in a thermally enhanced MLP package. The package includes
a thermal pad to provide an effective thermal contact between the device and the printed-circuit board (PCB).
Full PCB design guidelines for this package are provided in the application report entitled, QFN/SON PCB
Attachment (TI Literature Number SLUA271).
The most common measure of package thermal performance is thermal impedance (R_θJA) measured (or
modeled) from the device junction to the air surrounding the package surface (ambient). The mathematical
expression for R_θJA is:
R_qJA
=
T_J ^- T
P
A
(11)
Where:
• T_J = device junction temperature
• T_A = ambient temperature
• P = device power dissipation
Factors that can greatly influence the measurement and calculation of R_θJA include:
• Orientation of the device (horizontal or vertical)
• Volume of the ambient air surrounding the device under test and airflow
• Whether other surfaces are in close proximity to the device being tested
• Use multiple 10–13 mil vias in the PowerPAD™ to copper ground plane.
• Avoid cutting the ground plane with a signal trace near the power IC.
• The PCB must be sized to have adequate surface area for heat dissipation.
• FR4 (figerglass) thickness should be minimized.
The device power dissipation, P, is a function of the charge rate and the voltage drop across the internal Power
FET. It can be calculated from the following equation:
P = (V_(IN) - V_(OUT)) x I_O(OUT)
(12)
Due to the charge profile of Li-xx batteries, the maximum power dissipation is typically seen at the beginning of
the charge cycle when the battery voltage is at its lowest. See Figure 6.
Copyright © 2015, Texas Instruments Incorporated
Submit Documentation Feedback
19
Product Folder Links: bq24080-Q1 bq24081-Q1