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1.产品概述                       2.产品特点eTj嘉泰姆
3.应用范围                       4.下载产品资料PDF文档 eTj嘉泰姆
5.产品封装图                     6.电路原理图                   eTj嘉泰姆
7.功能概述                        8.相关产品eTj嘉泰姆

七,功能概述eTj嘉泰姆

Main Control LoopeTj嘉泰姆
The CXSD62144 is a constant frequency current mode switching regulator. During normal operation, the inter-eTj嘉泰姆
nal N-channel power MOSFET is turned on each cycle when the oscillator sets an internal RS latch and wouldeTj嘉泰姆
be turned off when an internal current comparator (ICMP) resets the latch. The peak inductor current at which ICMPeTj嘉泰姆
resets the RS latch is controlled by the voltage on the COMP pin, which is the output of the error amplifiereTj嘉泰姆
(EAMP). An external resistive divider connected between VOUT and ground allows the EAMP to receive an outputeTj嘉泰姆
feedback voltage VFB at FB pin. When the load current increases, it causes a slight decrease in VFB relative toeTj嘉泰姆
the 0.925V reference, which in turn causes the COMP voltage to increase until the average inductor currenteTj嘉泰姆
matches the new load current.eTj嘉泰姆
VIN Power-On-Reset (POR) and EN Under-voltage LockouteTj嘉泰姆
The CXSD62144 keep monitoring the voltage on VIN pin to prevent wrong logic operations which may occur wheneTj嘉泰姆
VIN voltage is not high enough for the internal control circuitry to operate. The VIN POR has a rising thresholdeTj嘉泰姆
of 4.05V (typical) with 0.3V of hysteresis.eTj嘉泰姆
An external under-voltage lockout (UVLO) is sensed atthe EN pin. The EN UVLO has a rising threshold of 2.5VeTj嘉泰姆
with 0.2V of hysteresis. The EN pin should be connected a resistor divider from VIN to EN .After the VIN and ENeTj嘉泰姆
voltages exceed their respective voltage thresholds, the IC starts a start-up process and then ramps up the outputeTj嘉泰姆
voltage to the setting of output voltage.eTj嘉泰姆
Over-Temperature Protection (OTP)eTj嘉泰姆
The over-temperature circuit limits the junction tempera-ture of the CXSD62144 When the junction temperature ex-eTj嘉泰姆
ceeds TJ =+160oC, a thermal sensor turns off the power MOSFET, allowing the device to cool down. The thermaleTj嘉泰姆
sensor allows the converter to start a start-up process and regulate the output voltage again after the junctioneTj嘉泰姆
temperature cools by 50oC.eTj嘉泰姆
The OTP designed with a 50 oC hysteresis lowers the average T J during c ontinuous thermal overload conditions,eTj嘉泰姆
increasing life time of the IC.eTj嘉泰姆
Enable/ShutdowneTj嘉泰姆
Driving EN to ground places the CXSD62144 in shutdown.When in shutdown, the internal N-Channel power MOSFET turns off, all internal circuitry shuts down and the quies-cent supply current reduces to 0.3μA.eTj嘉泰姆
Current-Limit ProtectioneTj嘉泰姆
The CXSD62144 monitors the output current, flowing through the N-Channel power MOSFET, and limits theeTj嘉泰姆
IC from damages during overload, short-circuit and over-voltage conditions.eTj嘉泰姆
Frequency FoldbackeTj嘉泰姆
The foldback frequency is controlled by the FB voltage.When the FB pin voltage is under 0.6V, the frequency ofeTj嘉泰姆
the oscillator will be reduced to 110kHz. This lower fre-quency allows the inductor current to safely discharge,eTj嘉泰姆
thereby preventing current runaway. The oscillator’s fre-quency will switch to its designed rate when the feedbackeTj嘉泰姆
voltage on FB rises above the rising frequency foldback threshold (0.6V, typical) again.eTj嘉泰姆
Over-Voltage ProtectioneTj嘉泰姆
The over-voltage function monitors the output voltage by FB pin. When the FB voltage increase over 120% of theeTj嘉泰姆
reference voltage, the over-voltage protection compara-tor will force the high-and low-side MOSFET gate drivereTj嘉泰姆
off. As soon as the output voltage is within regulation, the OVP comparator is disengaged. The chip will restore itseTj嘉泰姆
normal operation.eTj嘉泰姆
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