34652 datasheet(10/26 Pages) FREESCALE

10 / 26 page

Analog Integrated Circuit Device Data

Freescale Semiconductor

34652

FUNCTIONAL DESCRIPTION

INTRODUCTION

FUNCTIONAL DESCRIPTION

INTRODUCTION

Most telecom and data transfer networks require that

circuit boards be inserted and removed from the system

without powering down the entire system. When a circuit

board is inserted into or removed from a live backplane, the

filter or bypass capacitors at the input of the board’s power

module or switching power supply can cause large transient

currents when being charged or discharged. These currents

can cause severe and permanent damage to the boards, thus

making the system unstable. Figure 4 displays the inrush

current to the filter capacitor if a hot swap device is absent.

The inrush current reached an unsafe value of more than

55 A.

Figure 4. Circuit Board Insertion Without a

Hot Swap Device, Inrush Current Not Limited

The 34652 is an integrated negative voltage hot swap

controller with an internal Power MOSFET. The 34652

resides on the plug-in boards and allows the boards to be

safely inserted or removed by powering up the supply

voltages in a controlled manner and regulating the inrush

current to a user-programmable limit, thus allowing the

system to safely stabilize (see Figure 5). The 34652 provides

protection against overcurrent, undervoltage, overvoltage,

and overtemperature. Furthermore, it protects the system

from short circuits.

Figure 5. Circuit Board Insertion With the Hot Swap

Device, Inrush Current Limited

By integrating the control circuitry and the Power MOSFET

switch into a space-efficient package, the 34652 offers a

complete, cost-effective, and simple solution that takes much

less board space than a similar part with an external Power

MOSFET requires.

The 34652 can be used in -48 V telecom and networking

systems, servers, electronic circuit breakers, -48 V

distributed power systems, negative power supply control,

and central office switching.

FUNCTIONAL PIN DESCRIPTION

NEGATIVE SUPPLY INPUT VOLTAGE (VIN)

The VIN pin is the most negative power supply input. All

pins except the DISABLE pin are referenced to this input.

POWER GOOD OUTPUT (ACTIVE HIGH) (PG)

The PG pin is the active high power good output signal that

is used to enable or disable a load. This signal goes active

after a successful power-up sequence and stays active as

long as the device is in normal operation and is not

experiencing any faults.

The signal is deactivated under the following conditions:

• Power is turned off.

• The device is disabled for more than 1.0 ms.

• The device exceeded its thermal shutdown threshold for

more than 12

µs.

• The device is in overvoltage or undervoltage mode for

more than 1.0 ms.

• Load current exceeded the overcurrent limit for more than

3.0 ms.

This pin is referenced to VIN.

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