Datasheet

TPS24700

TPS24701

www.ti.com

SLVSAL3B – MARCH 2011– REVISED MAY 2011

SYSTEM OPERATION

INTRODUCTION

The TPS24700/1 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

• Adjustable overload timeout — also called an electronic circuit breaker

• Charge-complete indicator for downstream converter coordination

• A choice of latch (TPS24700) or automatic restart mode (TPS24701)

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

Figure 23 through Figure 24 and Figure 26 through Figure 28, demonstrate many of the functions described

previously.

BOARD PLUG IN

Figure 23 illustrates the inrush current that flows when a hot-swap board under the control of the TPS24700/1 is

plugged into an input power bus. Only the bypass capacitor charge current and small bias currents are evident

when a board is first plugged in. The TPS24700/1 is held inactive for a short period while internal voltages

stabilize. In this short period, GATE and TIMER are held low and PGb is held open-drain. When the voltage on

the internal VCC rail exceeds approximately 1.5 V, the power-on reset (POR) circuit initializes the TPS24700/1

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

GATE, TIMER, and PGb are released after the internal voltages have stabilized and the external EN (enable)

threshold has been exceeded. The part begins sourcing current from the GATE pin to turn on MOSFET M1. The

TPS24700/1 monitors the drain current passing through MOSFET M1 by measuring the voltage V

(VCC - SENSE)

Based on the measurement, the TPS24700/1 limits the drain current in the MOSFET to be no more than the

current limit I

LIM

, so as to alleviate the charging impact of the downstream bulk storage capacitors.

Figure 23. Inrush Mode at Hot-Swap Circuit Insertion

Product Folder Link(s): TPS24700 TPS24701