Detailed Description

The MAX5927/MAX5929 are circuit-breaker ICs for hot-

swap applications where a line card is inserted into a

live backplane. The MAX5927/MAX5929 operate down

to 1V provided one of the inputs is above 2.7V.

Normally, when a line card is plugged in to a live back-

plane, the card’s discharged filter capacitors provide

low impedance that can momentarily cause the main

power supply to collapse. The MAX5927/MAX5929

reside either on the backplane or on the removable

card to provide inrush current limiting and short-circuit

protection. This is achieved by using external N-chan-

nel MOSFETs, external current-sense resistors, and on-

chip comparators. The startup period and current-limit

threshold of the MAX5927/MAX5929 can be adjusted

with external resistors. Figure 1 shows the MAX5927/

MAX5929 functional diagram.

The MAX5927 offers four programmable current limits,

selectable fault management mode, and selectable

STAT_ output polarity. The MAX5929 features fixed cur-

rent limits, and a variety of fault management and

STAT_ polarity option combinations.

Mode

The MAX5927/MAX5929 supports three modes of oper-

ation: voltage-tracking, power-sequencing, and inde-

pendent mode. Select the appropriate mode according

to Table 1.

Voltage-Tracking Mode

Connect MODE high to enter voltage-tracking mode.

While in voltage-tracking mode, all channels turn on

and off together. To turn all channels on:

UVLO to startup delay (37.5ms).

• No faults may be present on any channel.

Low-Voltage, Quad, Hot-Swap

Controllers/Power Sequencers

_______________________________________________________________________________________

9

MODE

OPERATION

High (Connect to BIAS)

Voltage tracking

OPEN

Power sequencing

GND

Independent

Table 1. Operational Mode Selection

PIN

MAX5927

MAX5929

NAME

FUNCTION

21

—

LIM3

Channel 3 Current-Limit Setting. Connect a resistor from LIM3 to GND to set current-trip

level. Connect to GND for the default 25mV threshold. Do not leave open.

22

20

GATE2

Channel 2 Gate-Drive Output. Connect to gate of external N-channel MOSFET.

23

21

SENSE2

Channel 2 Current-Sense Input. Connect SENSE2 to the drain of an external MOSFET

24

22

IN2

Channel 2 Supply Input. Connect to a supply voltage from 1V to 13.2V and to one end of

25

—

LIM2

Channel 2 Current-Limit Setting. Connect a resistor from LIM2 to GND to set the current-

trip level. Connect to GND for the default 25mV threshold. Do not leave open.

26

23

ON4

On/Off Channel 4 Control Input (see the Mode section)

27

24

ON3

On/Off Channel 3 Control Input (see the Mode section)

28

1

MODE

Mode Configuration Input. Mode is configured according to Table 1 as soon as one of

the IN_ voltages exceeds UVLO and before turning on OUT_ (see the Mode section).

29

—

POL

STAT Output Polarity Select (See Table 3 and the Status Output Section)

30

2

ON2

On/Off Channel 2 Control Input (See the Mode Section)

31

3

ON1

On/Off Channel 1 Control Input (See the Mode Section)

32

—

LIM1

Channel 1 Current-Limit Setting. Connect a resistor from LIM1 to GND to set the current-

trip level. Connect to GND for the default 25mV threshold. Do not leave open.

EP

—

EP

Exposed Pad. Leave EP floating or connect to GND.

Pin Description (continued)