isl9211b Intersil Corporation, isl9211b Datasheet - Page 9

• Manufacturer Part Number: isl9211b
• Description: Charging System Safety Circuit
• Manufacturer: Intersil Corporation

persists, the FET shuts off again. This hiccup mode continues
until the OCP condition is cleared. Figures 8 and 9 show the
waveforms during power-up when the output is shorted to
ground.
Internal Over-Temperature Protection
The ISL9211B monitors its own internal temperature to prevent
thermal failures. When the internal temperature reaches
+150°C, the IC turns off the N-channel power MOSFET. The IC
does not resume operation until the internal temperature drops
below +110°C.
Fault Indication Output
The FAULT pin is an open-drain output that indicates a LOW
signal when any of the three fault events occurs. This provides a
signal to the microprocessor to take further action to enhance
the safety of the charging system.
Applications Information
The ISL9211B is designed to meet the “Lithium-Safe” criteria
when operating together with a qualified Li-ion battery charger.
The “Lithium-Safe” criteria require the charger output to fall
within the green region shown in Figure 15 under normal
operating conditions and not to fall within the red region when
there is a single fault in the charging system. Taking into account
the safety circuit in a Li-ion battery pack, the charging system is
allowed to have two faults without creating hazardous conditions
for the battery cell. The output of a Li-ion charger such as the
ISL6292C has a typical I-V curve (shown by the blue lines in
Figure 15) under normal operation (shown by the green region).
The function of the ISL9211B is to add a redundant protection
layer such that, under any single fault condition, the charging
system output does not exceed the I-V limits (shown by the red
lines). As Figure 15 shows, a charging system that includes the
ISL9211B and the ISL6292C chip set can easily meet the
“Lithium-Safe” test criteria.
The ISL9211B is a simple device that requires only three external
components, in addition to the ISL6292 charger circuit, to meet
the “Lithium-Safe” criteria (see “TYPICAL APPLICATION CIRCUIT”
R
82.5
49.9
35.7
22.6
61.9
41.2
31.6
24.9
(kΩ)
28
LIM
TABLE 1. CURRENT LIMIT RESISTOR SETTINGS
1000
1100
(mA)
OCP
300
400
500
600
700
800
900
9
R
11.3
9.53
19.1
16.5
15.4
12.4
10.5
(kΩ)
21
14
LIM
1200
1300
1400
1500
1600
1800
1900
2000
1700
(mA)
OCP
ISL9211B
on page 1. The selection of the current limit resistor,
given in “Overcurrent Protection (OCP)” on page 8.
R
R
terminal, in case the ISL9211B fails. The recommended value is
between 200kΩ and 1MΩ. With 200kΩ resistance, the
worst-case current flowing from the VB pin to the charger output
is shown in Equation 1, assuming VB pin voltage is 24V under
failure mode and battery voltage is 4.2V.
(
Such a small current can easily be absorbed by the bias current
of other components in a handheld system. Increasing the R
value reduces the worst-case current but at the same time
increases the error for the 4.34V battery OVP threshold.
The battery OVP threshold error is the original accuracy at the VB
pin given in the “Electrical Specifications” table on page 4, plus
the voltage built across R
VB pin leakage current is less than 20nA, as given in the
“Electrical Specifications” table on page 4. With a 200kΩ
resistor, the worst-case additional error is 4mV; with a 1MΩ
resistor, the worst-case additional error is 20mV.
Capacitor Selection
The input capacitor (C
on page 1) is for decoupling. A higher value reduces the voltage
drop or the over-shoot during transients.
Two scenarios can cause input voltage over-shoot. The first one is
when the AC adapter is inserted live (hot insertion). The second
one is when the current in the power NFET of the ISL9211B has a
step-down change. Figure 16 shows an equivalent circuit for the
ISL9211B input. The cable between the AC/DC converter output
and the handheld system input has a parasitic inductor. The
parasitic resistor is the sum of various components, such as the
cable, the adapter output capacitor ESR, the connector contact
resistance, and so on.
24V 4.2V
1000
VB
VB
prevents a large current from the VB pin to the battery
–
0
Selection
FIGURE 15. LITHIUM-SAFE OPERATING REGIONS
)
⁄
(
200kΩ
1
ISL9211B
LIMITS
ISL6292C
LIMITS
)
1
=
in the “TYPICAL APPLICATION CIRCUIT”
2
99μA
VB
BATTERY VOLTAGE (V)
by the VB pin leakage current. The
3
4
5
R
LIM
July 8, 2011
, is
FN7861.0
(EQ. 1)
VB
6