isl9209c Intersil Corporation, isl9209c Datasheet - Page 9

• Manufacturer Part Number: isl9209c
• Description: Charging System Safety Circuit
• Manufacturer: Intersil Corporation

R
The R
battery terminal, in case the ISL9209C fails. The
recommended value should be between 200kΩ to 1MΩ.
With 200kΩ resistance, the worst case current flowing from
the VB pin to the charger output is:
assuming the VB pin voltage is 30V under a failure mode
and the battery voltage is 4.2V. Such a small current can be
easily absorbed by the bias current of other components in
the handheld system. Increasing the R
worst case current, but at the same time increases the error
for the 4.34V battery OVP threshold.
The error of the battery OVP threshold is the original
accuracy at the VB pin given in the “Electrical Specifications”
table on page 2 plus the voltage built across the R
VB pin leakage current. The VB pin leakage current is less
than 20nA, as given in the Electrical Specifications table.
With the 200kΩ resistor, the worst-case additional error is
4mV and with a 1MΩ resistor, the worst-case additional error
is 20mV.
Interfacing to MCU
The ISL9209C has the enable (EN) and the warning (WRN)
digital signals that can be interfaced to a microcontroller unit
(MCU). Both signals can be left floating if not used. When
interfacing to an MCU, it is highly recommended to insert a
resistor between the ISL9209C signal pin and the MCU
GPIO pin, as shown in Figure 24. The resistor creates an
isolation to limit the current, in case a high voltage shows up
at the ISL9209C pins under a failure mode. The
recommended resistance ranges from 10kΩ to 100kΩ. The
selection of the R
the MCU. R
pin voltage is above the disable threshold when the GPIO
output of the MCU is high.
(
30V
1000
VB
–
Selection
0
VB
FIGURE 23. LITHIUM-SAFE OPERATING REGIONS
4.2V )
prevents a large current from the VB pin to the
EN
⁄
(
200kΩ
1
ISL9209
LIMITS
ISL6292C
LIMITS
should be selected so that the ISL9209C EN
EN
is dependent on the IO voltage (VIO) of
=
C
130μA
2
BATTERY VOLTAGE (V)
)
9
3
VB
4
value reduces the
5
VB
(EQ. 2)
by the
ISL9209C
6
Capacitor Selection
The input capacitor (C1 in the “Typical Application Circuit” 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 PFET of the ISL9209C has a step-down change.
Figure 25 shows an equivalent circuit for the ISL9209C
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 C2. The ISL9209C is designed to turn
off the power PFET slowly during the OCP, the battery OVP
event, and when the device is disabled via the EN pin.
Because of such design, the input over shoot during those
events is not significant. During an input OVP, however, the
PFET is turned in less than 1µs and can lead to significant
over shoot. Higher capacitance reduces this type of over
shoot.
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
FIGURE 25. EQUIVALENT CIRCUIT FOR THE ISL9209C INPUT
ISL9209
AC/DC
FIGURE 24. DIGITAL SIGNAL INTERFACE BETWEEN
Q
ADAPTER
5
C
C1
Q
4
ISL9209C AND MCU
R
5
L
WRN
EN
CABLE
R
R
PU
R
R
WRN
EN
VIO
C2
HANDHELD SYSTEM
May 21, 2007
ISL9209
MCU
FN6489.0
C