ACT8810
Active- Semi
Rev 4, 01-Oct-09
ActivePathTM CHARGER
FUNCTIONAL DESCRIPTION CONT’D
resulting from the current limit slew rate
(100mA/µS) limitations of the USB bus, the
CHG_IN bypass capacitance value must to be
between 4.7µF and 10µF for the ACT8810.
robustness and an absolute maximum voltage
rating of 14V for transients, attention must be given
to bypass techniques to ensure safe operation.
As a result, design of the CHG_IN bypass must
take care to “de-Q” the filter. This can be
accomplished by connecting a 1ꢀ resistor in series
with a ceramic capacitor (as shown in Figure 16), or
by using a tantalum or electrolytic capacitor to
utilize it’s higher ESR to dampen the ringing. For
additional protection in extreme situations, Zener
diodes with 12V clamp voltages may also be used.
In any case, it is always critical to evaluate voltage
transients at the ACT8810 CHG_IN pin with an
oscilloscope to ensure safe operation.
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
CHG_IN 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 CHG_IN pin is designed for maximum
Figure 16:
CHG_IN Bypass Options for USB or Wall Adaptor Supplies
Innovative PowerTM
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