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TPS2412PW Datasheet(PDF) 10 Page - Texas Instruments |
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TPS2412PW Datasheet(HTML) 10 Page - Texas Instruments |
10 / 29 page -470.02 R(RSET) V - 0.00314 (OFF) æ ö ç ÷ = ç ÷ è ø TPS2412, TPS2413 SLVS728C – JANUARY 2007 – REVISED NOVEMBER 2015 www.ti.com Feature Description (continued) GATE: Gate controls the external N channel MOSFET gate. GATE is driven positive with respect to A by a driver operating from the voltage on BYP. A time-limited high current discharge source pulls GATE to GND when the fast turnoff comparator is activated. The high-current discharge is followed by a sustaining pulldown. The turnoff circuits are disabled by the thermal shutdown, leaving a resistive pulldown to keep the gate from floating. The gate connection should be kept low impedance to maximize turnoff current. GND: This is the input supply reference. GND should have a low impedance connection to the ground plane. It carries several Amperes of rapid-rising discharge current when the external MOSFET is turned off, and also carries significant charge pump currents. RSET: A resistor connected from this pin to GND sets the fast V(A-C) comparator turnoff threshold. The threshold is slightly positive when the RSET pin is left open. Current drawn by the resistor programs the turnoff voltage to increasing negative values. The TPS2413 must have a negative threshold programmed to avoid an unstable condition at light load. The expression for R(RSET) in terms of the trip voltage, V(OFF), follows. (1) The units of the numerator are (V × V/A). V(OFF) is positive for V(A) greater than V(C), V(OFF) is less than 3 mV, and R(RSET) is in ohms. RSVD: Connect to ground. VDD: VDD is the primary supply for the gate drive charge pump and other internal circuits. This pin must be connected a source that is 3 V or greater when the external MOSFET is to be turned on. VDD may be greater or lower than the controlled bus voltage. A 0.01- μF bypass capacitor, or 10-Ω and a 0.01-μF filter, is recommended because charge pump currents are drawn through VDD. 8.3.2 TPS2412 vs TPS2413 – MOSFET Control Methods The TPS2412 control method yields several benefits. First, the low-current GATE driver provides a gentle turnon and turnoff for slowly rising and falling input voltage. Second, it reduces the tendency for on/off cycling of a comparator based solution at light loads. Third, it avoids reverse currents if the fast turnoff threshold is left positive. The drawback to this method is that the MOSFET appears to have a high resistance at light load when the regulation is active. A momentary output voltage droop occurs when a large step load is applied from a light- load condition. The TPS2412 is a better solution for a mid-rail bus that is re-regulated. The TPS2413 turns the MOSFET on if V(AC) is greater than 10 mV, and the rapid turnoff is activated at the programmed negative threshold. There is no linear control range and slow turnoff. The disadvantage is that the turnoff threshold must be negative (unless a minimum load is always present) permitting a continuous reverse current. Under a dynamic reverse voltage fault, the lower threshold voltage may permit a higher peak reverse current. There are a number of advantages to this control method. Step loads from a light load condition are handled without a voltage droop beyond I × R. If the redundant converter fails, applications with redundant synchronous converters may permit a small amount of reverse current at light load to assure that the MOSFET is all ready on. The TPS2413 is a better solution for low-voltage buses that are not re-regulated, and that may see large load steps transients. These applications recommendations are meant as a starting point, with the needs of specific implementations overriding them. 8.3.3 N+1 Power Supply – Typical Connection The N+1 power supply configuration shown in Figure 9 is used where multiple power supplies are paralleled for either higher capacity, redundancy or both. If it takes N supplies to power the load, adding an extra, identical unit in parallel permits the load to continue operation in the event that any one of the N supplies fails. The supplies are ORed together, rather than directly connected to the bus, to isolate the converter output from the bus when it is plugged-in or fails short. The TPS2412/13 with an external MOSFET emulates the function of the ORing diode. 10 Submit Documentation Feedback Copyright © 2007–2015, Texas Instruments Incorporated Product Folder Links: TPS2412 TPS2413 |
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