MAX5927A/MAX5929A–MAX5929D
t
D,UVLO
ensures that the board is fully inserted into the
backplane and that the input voltages are
stable. MAX5927A/MAX5929A–MAX5929D include a
UVLO glitch filter, t
D,GF
, to reject all input voltage noise
and transients. 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 MAX5929A/MAX5929B always latch the external
MOSFETs off when an overcurrent fault is detected,
and the MAX5929C/MAX5929D are always in autoretry
mode. The MAX5927A 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 MAX5929A/MAX5929B or MAX5927A (LATCH =
unconnected) fault and reinitiates the startup period.
Similarly, the MAX5929C/MAX5929D or MAX5927A
(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 MAX5927A (see Table 3). Tables 4 and 5 con-
tain the MAX5927A/MAX5929A–MAX5929D 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
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