Datasheet

TPS24720

www.ti.com

SLVSAL1C –MARCH 2011–REVISED SEPTEMBER 2013

SYSTEM OPERATION

INTRODUCTION

The TPS24720 provides all the features needed for a positive hot-swap controller. These features include:

• Undervoltage lockout

• Adjustable (system-level) enable

• Turn-on inrush limiting

• High-side gate drive for an external N-channel MOSFET

• MOSFET protection by power limiting

• Adjustable overload timeout, also called an electronic circuit breaker

• Charge-complete indicator for downstream converter coordination

• A choice of latch or automatic restart mode

• A low-power disable mode accessed by holding ENSD low

• MOSFET short detection

• Load overvoltage protection

The typical application diagram, shown on the front page of this datasheet, and oscilloscope plots, shown in

Figure 29 through Figure 31 and Figure 33 through Figure 36, demonstrate many of the functions described

previously.

BOARD PLUG-IN

Figure 29 and Figure 30 illustrate the inrush current that flows when a hot swap board under the control of the

TPS24720 is plugged into a system bus. Only the bypass capacitor charge current and small bias currents are

evident when a board is first plugged in. The TPS24720 is held inactive for a short period while internal voltages

stabilize. In this short period, GATE, PROG, and TIMER are held low and PGb, FLTb, and FFLTb are held open-

drain. When the voltage on the internal VCC rail exceeds approximately 1.5 V, the power-on reset (POR) circuit

initializes the TPS24720 and a start-up cycle is ready to take place.

GATE, PROG, TIMER, PGb, FLTb and FFTb are released after the internal voltages have stabilized and the

external EN (enable) thresholds have been exceeded. The part begins sourcing current from the GATE pin to

turn on MOSFET M

. The TPS24720 monitors both the drain-to-source voltage across MOSFET M

and the

drain current passing through it. Based on these measurements, the TPS24720 limits the drain current by

controlling the gate voltage so that the power dissipation within the MOSFET does not exceed the power limit

programmed by the user. The current increases as the voltage across the MOSFET decreases until finally the

current reaches the current limit I

LIM

Product Folder Links: TPS24720