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Zakładka z wyszukiwarką danych komponentów |
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LTM4636-1 Arkusz danych(PDF) 12 Page - Linear Technology |
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LTM4636-1 Arkusz danych(HTML) 12 Page - Linear Technology |
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12 / 38 page  LTM4636-1 12 46361fa For more information www.linear.com/LTM4636-1 OPERATION A TEMP+ and TEMP– pins are provided to allow the internal device temperature to be monitored using an onboard diode connected NPN transistor. High efficiency at light loads can be accomplished with selectable Burst Mode operation using the MODE_PLLIN pin. These light load features will accommodate battery operation. Efficiency graphs are provided for light load op- erationintheTypicalPerformanceCharacteristicssection. APPLICATIONS INFORMATION The typical LTM4636-1 application circuit is shown in Figure 20. External component selection is primarily determined by the maximum load current and output voltage. Refer to Table 5 for specific external capacitor requirements for particular applications. VIN to VOUT Step-Down Ratios TherearerestrictionsintheVINtoVOUTstep-downratiothat can be achieved for a given input voltage. The maximum duty cycle is 94% typical at 500kHz operation. The VIN to VOUT minimum dropout is a function of load current and operation at very low input voltage and high duty cycle applications. At very low duty cycles the minimum 100ns on-time must be maintained. See the PLL, Frequency Adjustment and Synchronization section and temperature derating curves. Output Voltage Programming The PWM controller has an internal 0.6V ±1% reference voltage. As shown in the Block Diagram, a 4.99k internal feedback resistor connects the VOUTS1 and VFB pins to- gether. When the remote sensing is used, then VOUTS1+ and VOUTS1– are connected to the remote VOUT and GND points. If no remote sense the VOUTS1+ connects to VOUT. The output voltage will default to 0.6V with no feedback resistor.AddingaresistorRFBfromVFBtogroundprograms the output voltage: VOUT 0.6V • 4.99k RFB RFB Table 1. VFB Resistor Table vs Various Output Voltages VOUT (V) 0.6 1.0 1.2 1.5 1.8 2.5 3.3 RFB (k) Open 7.5 4.99 3.24 2.49 1.58 1.1 For parallel operation of N LTM4636-1s, the following equation can be used to solve for RFB: RFB 4.99k / N VOUT 0.6V – 1 Or use VOUTS1 on one channel and connect all feedback pins together utilizing a single feedback resistor. Tie the VFB pins together for each parallel output. The COMP pins must be tied together also. See the Typical Applications section examples. Input Capacitors The LTM4636-1 module should be connected to a low AC-impedance DC source. Additional input capacitors are neededfortheRMSinputripplecurrentrating.TheICIN(RMS) equation which follows can be used to calculate the input capacitor requirement. Typically 22µF X7R ceramics are a good choice with RMS ripple current ratings of ~4A each. A47µFto100µFsurfacemountaluminumelectrolyticbulk capacitor can be used for more input bulk capacitance. This bulk input capacitor is only needed if the input source impedanceiscompromisedbylonginductiveleads,traces ornotenoughsourcecapacitance.Iflowimpedancepower planes are used, then this bulk capacitor is not needed. For a buck converter, the switching duty cycle can be estimated as: D VOUT VIN |
Podobny numer części - LTM4636-1 |
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Podobny opis - LTM4636-1 |
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