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ISL9209IRZ Datasheet(PDF) 8 Page - Intersil Corporation |
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ISL9209IRZ Datasheet(HTML) 8 Page - Intersil Corporation |
8 / 11 page 8 FN6274.0 April 25, 2006 protection threshold is set to 5.85V. When the input voltage 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 the Electrical Specification. When the input overvoltage condition is removed, the ISL9209 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 4.4V battery OVP threshold. The threshold has 75mV 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 ISL9209. The resistor between the VB pin and the battery, RVB, as shown in the Typical Applications circuit, 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 200k Ω 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 the following equation: 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 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 ISL9209 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 ISL9209 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 200k Ω 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 ISL9209 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 ISL9209 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 with the red lines. As a result, the charging system adopting the ISL9209 and the ISL6292C chip set can easily pass the “Lithium-Safe” criteria test procedures. The ISL9209 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. The selection of the current limit resistor RILIM is given in the Overcurrent Protection section. I LIM 0.8V R ILIM --------------- 31250 25000 R ILIM ---------------- = ⋅ = ISL9209 |
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