AAT2601 Datasheet, PDF (26/38 Pages) Advanced Analogic Technologies – Total Power Solution for Portable Applications

PRODUCT DATASHEET
AAT2601178
Total Power Solution for Portable Applications
maximum voltage rating of +6.5V for transients, atten-
tion must be given to bypass techniques to ensure safe
operation. As a result, design of the CHGIN bypass must
take care to “de-Q” the filter. This can be accomplished
by connecting a 1Ω resistor in series with a ceramic
capacitor (as shown in Figure 6A), or by bypassing with
a tantalum or electrolytic capacitor to utilize its higher
ESR to dampen the ringing (as shown in Figure 6A). For
additional protection, Zener diodes with 6V clamp volt-
ages may also be used. In any case, it is always critical
to evaluate voltage transients at the CHGIN pin with an
oscilloscope to ensure safe operation.
Thermal Considerations
The actual maximum charging current is a function of
charge adapter input voltage, the state of charge of the
battery at the moment of charge, the system supply cur-
rent from SYSOUT, and the ambient temperature and the
thermal impedance of the package and printed circuit
board. The maximum programmable current may not be
achievable under all operating parameters. One issue to
consider is the amount of current being sourced to the
SYSOUT pin from the CHGIN LDO while the battery is
being charged.
The AAT2601 is offered in a TQFN55-36 package which
can provide up to 4W of power dissipation when it is
properly bonded to a printed circuit board and has a
maximum thermal resistance of 25°C/W. Many consider-
ations should be taken into account when designing the
printed circuit board layout, as well as the placement of
the charger IC package in proximity to other heat gen-
erating devices in a given application design. The ambi-
ent temperature around the charger IC will also have an
effect on the thermal limits of a battery charging applica-
tion. The maximum limits that can be expected for a
given ambient condition can be estimated by the follow-
ing discussion. First, the maximum power dissipation for
a given situation should be calculated:
P_D(MAX) =
(T_J(MAX) - T_A)
θ_JA
Where:
P_D(MAX) = Maximum Power Dissipation (W)
θ_JA = Package Thermal Resistance (°C/W)
T_J(MAX) = Maximum Device Junction Temperature (°C)
[150°C]
T_A = Ambient Temperature (°C)
To USB Port or
Wall Adapter
CHGIN
1Ω
1μF Ceramic
(XR5/XR7)
To USB Port or
Wall Adapter
CHGIN
4.7μF
ESR > 1Ω
(A)
(B)
Figure 6: Hot Plug Requirements.
26
www.analogictech.com
2601.2008.01.1.0