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七,功能概述 Main Control Loop The JTMT1465 is a constant frequency, synchronous rectifier and current-mode switching regulator. In normal operation,the internal upper power MOSFET is turned on each cycle.The peak inductor current at which ICMP turn off the upper MOSFET is controlled by the voltage on the COMP node,which is the output of the error amplifier (EAMP). An external resistive divider connected between Vout and ground allows the EAMP to receive an output feedback voltage VFB at FB pin. When the load current increases, it causes a slightly decrease in VFB relative to the 0.8V reference, which in turn causes the COMP voltage to increase until the average inductor current matches the new load current. VIN Power-On-Reset (POR) The JTMT1465 keep monitoring the voltage on VIN pin to prevent wrong logic operations which may occur when VIN voltage is not high enough for the internal control circuitry to operate. The VIN POR has a rising threshold of 3.9V (typical) with 0.6V of hysteresis.After the VIN voltages exceed its respective POR thresholds,the IC starts a start-up process and then ramps up the output voltage to the setting of output voltage. Connect a RC network from EN to GND to set a turn-on delay that can be used to sequence the output voltages of multiple devices. Enable/ShuJTMTown Driving EN to ground places the JTMT1465 in shuJTMTown. When in shuJTMTown, the internal power MOSFETes turn off, all internal circuitry shuts down and the quiescent supply current of VlN reduces to <10µA, the EN under- voltage-lockout (UVLO) has a rising threshold of 1.4V(typical) with 0.2V of hysteresis. Soft-Start The JTMT1465 provides built-in soft-start function to limit the inrush current. The soft-start time is 1ms。 Bootstrap Capacitor The JTMT1465 is a N-channel MOSFET step down converter.The MOSFET requires a gate voltage that is higher than input voltage, thus a boost capacitor should be connected between SW and BST pins to drive the gate of the N-channel MOSFET. Typical boostrap capacitor value is from 10nF to 100nF. Over-Current-Protection and Hiccup The JTMT1465 has a cycle-by-cycle over-current limit when the inductor current peak value exceeds the set current limit threshold. Meanwhile, the output voltage drops until FB is below the Under-Voltage (UV) threshold below the reference. Once UV is triggered, the JTMT1465 enters hiccup mode to periodically restart the part. This protection mode is especially useful when the output is dead-shorted to ground. The average short circuit current is greatly reduced to alleviate thermal issues and to protect the regulator. The JTMT1465 exits the hiccup mode once the over-current condition is removed. Over-Temperature Protection (OTP)
The over-temperature circuit limits the junction temperature of the JTMT1465. When the junction temperature
exceeds 150ºC, a thermal sensor turns off the N-channel power MOSFET, allowing the device to cool down. Thethermal sensor allows the converter to start a start-up process and regulate the output voltage again after the junction temperature cools by 30ºC. The OTP designed with a 30ºC hysteresis lowers the average TJ during continuous thermal overload conditions, increasing life time of the JTMT1465. 八,相关产品
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