ISL9212BIRZ-T Intersil, ISL9212BIRZ-T Datasheet - Page 8

• Manufacturer Part Number: ISL9212BIRZ-T
• Description: IC SAFETY SYSTEM CHARGER 12-TDFN
• Manufacturer: Intersil

Specifications of ISL9212BIRZ-T

• Function: Battery Monitor
• Battery Type: Lithium-Ion (Li-Ion)
• Voltage - Supply: 4.3 V ~ 6.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 12-TDFN
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

exceeds the threshold, the CP1 outputs a logic signal to turn
off the power PFET within 1µs (see Figure 3) to prevent the
high input voltage from damaging the electronics in the
handheld system. The hysteresis for the input OVP
threshold is given in “Electrical Specifications” on page 2.
When the input overvoltage condition is removed, the
ISL9212B re-enables the output by running through the soft-
start, as shown in Figure 5. Because of the 10ms second
delay before the soft-start, the output is never enabled if the
input rises above the OVP threshold quickly, as shown in
Figure 6.
Battery Overvoltage Protection
The battery voltage OVP is realized with the VB pin. The
comparator CP3, as shown in Figure 1, monitors the VB pin
and issues an overvoltage signal when the battery voltage
exceeds the 4.34V battery OVP threshold. The threshold
has 30mV built-in hysteresis. The comparator CP3 has a
built-in 180µs blanking time to prevent any transient voltage
from triggering the OVP. If the OVP situation still exists after
the blanking time, the power PFET is turned off. The control
logic contains a 4-bit binary counter that if the battery
overvoltage event occurs 16 times, the power PFET is
turned off permanently, as shown in Figure 7. Recycling the
input power or toggling the enable (EN) input will reset the
counter and restart the ISL9212B.
The resistor between the VB pin and the battery, R
shown in the “Typical Application Circuit” on page 1) is an
important component. This resistor provides a current limit in
case the VB pin is shorted to the input voltage under a failure
mode. The VB pin leakage current under normal operation is
negligible to allow a resistance of 200kΩ to 1MΩ be used.
Overcurrent Protection (OCP)
The current in the power PFET is limited to prevent charging
the battery with an excessive current. The current is sensed
using the voltage drop across the power FET after the FET is
turned on. The reference of the OCP is generated using a
sensing FET Q2, as shown in Figure 1. The current in the
sensing FET is forced to the value programmed by the ILIM
pin. The size of the power FET Q1 is 31,250 times the size
of the sensing FET. Therefore, when the current in the power
FET is 31,250 times the current in the sensing FET, the drain
voltage of the power FET falls below that of the sensing FET.
The comparator CP2 then outputs a signal to turn off the
power FET.
The OCP threshold can be calculated using Equation 1:
where the 0.8V is the regulated voltage at the ILIM pin. The
OCP comparator CP2 has a built-in 170µs delay to prevent
false triggering by transient signals. The OCP function also
has a 4-bit binary counter that accumulates during an OCP
event. When the total count reaches 16, the power PFET is
I
LIM
=
--------------- 31250
R
0.8V
ILIM
⋅
=
25000
--------------- -
R
ILIM
8
VB,
(EQ. 1)
(as
ISL9212B
turned off permanently, unless the input power is recycled or
the enable pin is toggled. Figure 8 and Figure 9 illustrate the
waveforms during the power-up when the output is
short-circuited to ground.
Internal Over-Temperature Protection
The ISL9212B monitors its own internal temperature to
prevent thermal failures. When the internal temperature
reaches +140°C, the IC turns off the P-Channel power
MOSFET. The IC does not resume operation until the
internal temperature drops below +90°C.
External Enable Control
The ISL9212B offers an enable (EN) input. When the EN pin
is pulled to logic HIGH, the protection IC is shut down. The
internal control circuit as well as the power PFET are turned
off. Both 4-bit binary counters for the battery OVP and the
OCP are reset to zero when the IC is re-enabled. The EN pin
has an internal 200kΩ pull-down resistor. Leaving the EN pin
floating or driving it to below 0.4V enables the IC.
Warning Indication Output
The WRN pin is an open-drain output that indicates a LOW
signal when any of the three protection events happens. This
allows the microprocessor to give an indication to the user to
further enhance the safety of the charging system.
Applications Information
The ISL9212B is designed to meet the “Lithium-Safe” criteria
when operating together with the ISL6292 family Li-ion
battery chargers. The “Lithium-Safe” criteria requires the
charger output to fall within the green region shown in
Figure 23 under normal operating conditions and NOT to fall
in 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 any ISL6292 family chargers, such as the
ISL6292C, has a typical I-V curve shown with the blue lines
under normal operation, which is within the green region.
The function of the ISL9212B is to add an redundant
protection layer such that, under any single fault condition,
the charging system output does not exceed the I-V limits
shown with the red lines. As a result, the charging system
adopting the ISL9212B and the ISL6292C chip set can
easily pass the “Lithium-Safe” criteria test procedures.
The ISL9212B is a simple device that requires only three
external components, in addition to the ISL6292 charger
circuit, to meet the “Lithium-Safe” criteria, as shown in the
“Typical Application Circuit” on page 1. The selection of the
current limit resistor R
(OCP)” on page 8.
ILIM
is given in “Overcurrent Protection
March 21, 2007
FN6399.0