AAT3601_08 Datasheet, PDF (27/37 Pages) Advanced Analogic Technologies – Total Power Solution for Portable Applications

PRODUCT DATASHEET
AAT3601178
Total Power Solution for Portable Applications
Event Description
No battery charging activity.
Battery charging
Charging completed
STAT
Low (to GND)
High (to V_OUT1)
Low (to GND)
Table 3: Charge Status Output (STAT).
CHGIN Bypass Capacitor Selection
CHGIN is the power input for the AAT3601 battery char-
ger. The battery charger is automatically enabled when-
ever a valid voltage is present on CHGIN. In most appli-
cations, CHGIN is connected to either a wall adapter or
USB port. Under normal operation, the input of the char-
ger will often be “hot-plugged” directly to a powered USB
or wall adapter cable, and supply voltage ringing and
overshoot may appear at the CHGIN pin. A high quality
capacitor connected from CHGIN to G, placed as close as
possible to the IC, is sufficient to absorb the energy. Wall-
adapter powered applications provide flexibility in input
capacitor selection, but the USB specification presents
limitations to input capacitance selection. In order to
meet both the USB 2.0 and USB OTG (On The Go) spec-
ifications while avoiding USB supply under-voltage condi-
tions resulting from the current limit slew rate (100mA/
μs) limitations of the USB bus, the CHGIN bypass capac-
itance value must to be between 1μF and 4.7μF. Ceramic
capacitors are often preferred for bypassing applications
due to their small size and good surge current ratings,
but care must be taken in applications that can encounter
hot plug conditions as their very low ESR, in combination
with the inductance of the cable, can create a high-Q
filter that induces excessive ringing at the CHGIN pin.
This ringing can couple to the output and be mistaken as
loop instability, or the ringing may be large enough to
damage the input itself. Although the CHGIN pin is
designed for maximum robustness and an absolute max-
imum voltage rating of +6.5V for transients, attention
must be given to bypass techniques to ensure safe oper-
ation. 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 capaci-
tor (as shown in Figure 8A), or by bypassing with a tan-
talum or electrolytic capacitor to utilize its higher ESR to
dampen the ringing, as shown in Figure 8B. For addi-
tional protection, Zener diodes with 6V clamp voltages
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. The maximum pro-
grammable current may not be achievable under all oper-
ating parameters. Issues to consider are the amount of
current being sourced to the SYSOUT pin from the CHGIN
LDO at the same time as the charge current to BAT.
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 8: Hot Plug Requirements.
3601.2008.07.1.1
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