BQ24081_12 Datasheet, PDF (17/25 Pages) Texas Instruments – 1-A, SINGLE-CHIP, LI-ION AND LI-POL CHARGER IC

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bq24080
bq24081
SLUS698E – MARCH 2006 – REVISED AUGUST 2011
SOURCE
INPUT
VDC
GND
C₁
0.1 mF
bq24080
1 IN
OUT 10
1.5 kW
2 GND
CE 9
1.5 kW
PACK+
C₂
+
0.1 mF _PACK–
1.5 kW
3 STAT1 PG 8
4 STAT2 GND 7
5 V_SS
ISET 6
1.13 kW
R_SET
Charge Current
Translator Output
Figure 10. Typical Application Circuit
Thermal Considerations
The bq24080 and bq24081 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
(5)
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)
(6)
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.
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