ISL9211B
10
FN7861.1
November 4, 2014
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During the load current step-down transient, the energy stored in
the parasitic inductor is used to charge the input decoupling
capacitor, C
2
. The ISL9211B is designed to turn off the power
NFET slowly during an OCP and battery OVP event. Because of
this design, the input over-shoot during these events is not
significant. During an input OVP, however, the NFET is turned in
less than 1µs and can lead to significant over-shoot. Higher
capacitance reduces the over-shoot.
Over-shoot caused by a hot insertion is not very dependent on the
decoupling capacitance value, especially when ceramic type
capacitors are used for decoupling. In theory, over-shoot can rise
up to twice the DC output voltage of the AC adapter. Actual peak
voltage is dependent on the damping factor that is mainly
determined by parasitic resistance (R in Figure 16).
The recommended input decoupling capacitor is a 25V, X5R
dielectric ceramic capacitor with a value between 0.1µF and 1µF.
The output of the ISL9211B and the input of the charging circuit
typically share one decoupling capacitor. Selection of that
capacitor is determined mainly by the requirements of the
charging circuit. When using the ISL6292 family of chargers, a
1µF, 6.3V, X5R capacitor is recommended.
Layout Recommendation
The ISL9211B uses a thermally enhanced TDFN package with an
exposed thermal pad at the bottom of the package. The layout
should include as much copper as possible beneath the exposed
pad on the component layer to improve thermal performance.
The exposed pad under the package should be connected to the
ground plane electrically as well as thermally. The vias should be
about 0.3mm to 0.33mm in diameter. Use as many vias as will fit
in the thermal pad area.
FIGURE 16. EQUIVALENT CIRCUIT FOR ISL9211B INPUT
AC/DC ISL9211B
ADAPTER CABLE HANDHELD SYSTEM
C1 L R C2
