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SM72485 数据表(PDF) 6 Page - Texas Instruments |
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SM72485 数据表(HTML) 6 Page - Texas Instruments |
6 / 23 page Q Q FB VIN VCC SW RTN ON TIMER DRIVER Vin BST LEVEL SHIFT THERMAL SHUTDOWN FINISH START RCL FINISH START RT L1 R VCC UVLO FB D1 UVLO REGULATION COMPARATOR SD FINISH START REGULATOR CURRENT LIMIT OFF TIMER SHUTDOWN GD BUCK SWITCH CURRENT SENSE GND 7V BIAS BYPASS SWITCH RT 2.875V VINSENSE Q2 C1 C5 6V to 95V Input RT/SD 0.7V 300 ns MIN OFF TIMER CLR R SET S C2 C3 VOUT R3 RFB1 FB2 RCL RCL 2.5A OVER-VOLTAGE COMPARATOR CHARGE PRE - C4 SM72485 0.3A SM72485 SNVS697D – JANUARY 2011 – REVISED APRIL 2013 www.ti.com BLOCK DIAGRAM FUNCTIONAL DESCRIPTION The SM72485 Step Down Switching Regulator features all the functions needed to implement a low cost, efficient, Buck bias power converter. This high voltage regulator contains a 100 V N-Channel Buck Switch, is easy to implement and is provided in the VSSOP and the thermally enhanced WSON package. The regulator is based on a control scheme using an on-time inversely proportional to VIN. The control scheme requires no loop compensation. Current limit is implemented with forced off-time, which is inversely proportional to VOUT. This scheme ensures short circuit control while providing minimum foldback. The SM72485 can be applied in numerous applications to efficiently regulate down higher voltages. This regulator is well suited for high voltage PV panel junction boxes, 48 Volt Telecom and the new 42V Automotive power bus ranges. Features include: Thermal Shutdown, VCC under-voltage lockout, Gate drive under-voltage lockout, Max Duty Cycle limit timer, intelligent current limit off timer, and a pre-charge switch. Control Circuit Overview The SM72485 is a Buck DC-DC regulator that uses a control scheme in which the on-time varies inversely with line voltage (VIN). Control is based on a comparator and the on-time one-shot, with the output voltage feedback (FB) compared to an internal reference (2.5V). If the FB level is below the reference the buck switch is turned on for a fixed time determined by the line voltage and a programming resistor (RT). Following the ON period the switch will remain off for at least the minimum off-timer period of 300ns. If FB is still below the reference at that time the switch will turn on again for another on-time period. This will continue until regulation is achieved. The SM72485 operates in discontinuous conduction mode at light load currents, and continuous conduction mode at heavy load current. In discontinuous conduction mode, current through the output inductor starts at zero and ramps up to a peak during the on-time, then ramps back to zero before the end of the off-time. The next on- time period starts when the voltage at FB falls below the internal reference - until then the inductor current remains zero. In this mode the operating frequency is lower than in continuous conduction mode, and varies with load current. Therefore at light loads the conversion efficiency is maintained, since the switching losses reduce with the reduction in load and frequency. The discontinuous operating frequency can be calculated as follows: 6 Submit Documentation Feedback Copyright © 2011–2013, Texas Instruments Incorporated Product Folder Links: SM72485 |
类似零件编号 - SM72485 |
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类似说明 - SM72485 |
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