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MAX5927/MAX5929

age. t

D,UVLO

ensures that the board is fully inserted

into the backplane and that the input voltages are

stable. The MAX5927/MAX5929 include a UVLO glitch

filter, t

D,GF

, to reject all input voltage noise and tran-

sients. Bringing all input supplies below the UVLO

threshold for longer than t

D,GF

reinitiates t

D,UVLO

and

the startup period, t

START

. See Figure 8 for an example

of automatic turn-on function.

Latched and Autoretry Fault Management

The MAX5929L always latch the external MOSFETs off

when an overcurrent fault is detected, and the

MAX5929A are always in autoretry mode. The

MAX5927 can be configured to either latch the external

MOSFETs off or to autoretry (see Table 2). Toggling

ON_ below 0.875V for at least 100µs clears the

MAX5929L or MAX5927 (LATCH = FLOAT) fault and

reinitiates the startup period. Similarly, the MAX5929A

or MAX5927 (LATCH = GND) turn the external

MOSFETs off when an overcurrent fault is detected,

then automatically restart after the autoretry delay that

is internally set to 64 times t

START

Status Outputs (STAT_)

The status (STAT_) outputs are open-drain outputs that

assert when hot swap is successful and t

START

has

elapsed. STAT_ deasserts if ON_ is low or if the chan-

nel is turned off for any fault condition.

The polarity of the STAT_ outputs is selected using POL

for the MAX5927 (see Table 3). Tables 4 and 5 contain

the MAX5927/MAX5929 truth tables.

Applications Information

Component Selection

N-Channel MOSFETs

Select the external MOSFETs according to the applica-

tion’s current levels. Table 6 lists recommended com-

ponents. The MOSFET’s on-resistance (R

DS(ON)

)

should be chosen low enough to have a minimum volt-

age drop at full load to limit the MOSFET power dissi-

pation. High R

DS(ON)

causes output ripple if there is a

pulsating load. Determine the device power rating to

accommodate a short-circuit condition on the board at

startup and when the device is in autoretry mode (see

the MOSFET Thermal Considerations section).

Using these devices in latched mode allows the use of

MOSFETs with lower power ratings. A MOSFET typical-

ly withstands single-shot pulses with higher dissipation

than the specified package rating. Table 7 lists some

recommended MOSFET manufacturers.

Low-Voltage, Quad, Hot-Swap

Controllers/Power Sequencers

16 ______________________________________________________________________________________

LATCH FAULT MANAGEMENT

Floating Fault condition latches MOSFETs off

Low Autoretry mode

Table 2. Selecting Fault Management

Mode (MAX5927)

POL STAT_

Low Asserts low

Floating Asserts high (open drain)

Table 3. Selecting STAT_ Polarity

(MAX5927)

Figure 8. Automatic Turn-On when Input Voltages are Above

their Respective Undervoltage Lockout Threshold (Provided

UVLO

Requirement is Met)

MAX5927

MAX5929

ON1

ON2

ON3

ON4

GND

ON1

ON2

ON3

ON4

REMOVABLE CARDBACKPLANE