ISL9211AIRU48XZ-T Intersil, ISL9211AIRU48XZ-T Datasheet - Page 10

• Manufacturer Part Number: ISL9211AIRU48XZ-T
• Description: IC SAFETY CIRCUIT CHARGE 8UTDFN
• Manufacturer: Intersil

Specifications of ISL9211AIRU48XZ-T

• Function: Battery Monitor
• Battery Chemistry: Lithium-Ion (Li-Ion)
• Voltage - Supply: 4.3 V ~ 24 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-UFDFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

FIGURE 15. EQUIVALENT CIRCUIT FOR THE ISL9211A
Capacitor Selection
The input capacitor (C
on page 1) is for decoupling. Higher value reduces the
voltage drop or the over-shoot during transients.
Two scenarios can cause the input voltage over-shoot. The
first one is when the AC adapter is inserted live (hot
insertion) and the second one is when the current in the
power NFET of the ISL9211A has a step-down change.
Figure 15 shows an equivalent circuit for the ISL9211A
input. The cable between the AC/DC converter output and
the handheld system input has a parasitic inductor. The
parasitic resistor is the lumped sum of various components,
such as the cable, the adapter output capacitor ESR, the
connector contact resistance, and so on.
During the load current step-down transient, the energy
stored in the parasitic inductor is used to charge the
input decoupling capacitor C
to turn off the power NFET slowly during the OCP and the
battery OVP event. Because of such design, the input
over-shoot during those 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.
AC/DC
ADAPTER
C1
INPUT
L
1
CABLE
in the “Typical Application Circuit”
10
2
R
. The ISL9211A is designed
HANDHELD SYSTEM
C2
ISL9211A
ISL9211A
The 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, the over-shoot can rise up to twice
of the DC output voltage of the AC adapter. The actual
peak voltage is dependent on the damping factor that is
mainly determined by the parasitic resistance (R in
Figure 15).
In practice, the input decoupling capacitor is
recommended to use a 25V, X5R dielectric ceramic
capacitor with a value between 0.1µF to 1µF.
The output of the ISL9211A and the input of the charging
circuit typically share one decoupling capacitor. The
selection of that capacitor is mainly determined by the
requirement of the charging circuit. When using the
ISL6292 family chargers, a 1µF, 6.3V, X5R capacitor is
recommended.
Layout Recommendation
The ISL9211A uses a thermal-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 possible to fit in the epad area.
August 25, 2010
FN6702.1