-470.02

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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.

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

(1)

RSVD: Connect to ground.

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

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.

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

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