1V to 13.2V, n-Channel Hot-Swap Controllers

Require No Sense Resistor

10

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Detailed Description

The MAX5924/MAX5925/MAX5926 are hot-swap con-

troller ICs designed for applications where a line card is

inserted into a live backplane. Normally, when a line card

is plugged into a live backplane, the card’s discharged

filter capacitors provide a low impedance that can

momentarily cause the main power supply to collapse.

The MAX5924/MAX5925/MAX5926 are designed to

reside either in the backplane or in the removable card

to provide inrush current limiting and short-circuit pro-

tection. This is achieved using an external n-channel

MOSFET and an optional external current-sense resistor.

Several critical parameters can be programmed:

• Slew rate (inrush current)

• Circuit-breaker threshold

• Turn-on voltage

• Fault-management mode (MAX5926)

• Circuit-breaker temperature coefficient (MAX5926)

See the Selector Guide for a device-specific list of fac-

tory-preset features and parameters.

Startup Mode

The MAX5924/MAX5925/MAX5926 control an external

MOSFET connected in series with the hot-swapped

undervoltage lockout threshold or when the device is

disabled (see the EN (MAX5924/MAX5925, EN1/EN2

the MAX5924/MAX5925/MAX5926 are enabled, an

During the first stage of startup, the MAX5924/

MAX5925/MAX5926 detect whether an external sense

resistor is present and autoconfigure accordingly

(Figure 4). Bilevel fault protection temporarily disables,

and load-probing circuitry enables, if no sense resistor

is detected (see the Load Probing section). During load

the device manages the fault according to the selected

fault-management mode (see the Latched and

MAX5926 begin startup (Figure 5). If an external

bilevel fault protection enables with a startup circuit-

accommodate the higher-than-normal inrush current

During startup, the MAX5924/MAX5925/MAX5926 gradu-

mined by the selected slew rate, SR (see the Slew Rate

and the MAX5924/MAX5925/MAX5926 enable standard

bilevel fault protection (see the Bilevel Fault Protection

section).

LOAD

PROBE*

AUTODETECT

PRESENT

ABSENT

SLEW-RATE-

LIMITED STARTUP

SUCCESS

FAILURE

FAULT

MANAGEMENT

NORMAL

OPERATION

Figure 4. Startup Flow Chart

IPROBE

(0.2V typ)

SR = dV

dt

SR = dV

dt

Figure 5. Startup Waveform