max5938 Maxim Integrated Products, Inc., max5938 Datasheet - Page 11

• Manufacturer Part Number: max5938
• Description: Max5938 -48v Hot-swap Controller With Vin Step Immunity, No Rsense, And Overvoltage Protection
• Manufacturer: Maxim Integrated Products, Inc.

Fault management can be triggered by the following
conditions:
• V
• V
• V
• Load-probe test fails,
• V
Once in the fault management mode, GATE will always be
pulled to V
always deasserts PGOOD. If CB_ADJ is left open, short-
circuit and circuit-breaker faults are ignored. The
MAX5938A version has automatic retry following a fault
while the MAX5938L remains latched in the fault condition.
If the MAX5938A entered fault management due to an
OV fault, it will start the autoretry timer when the OV
fault is removed. For circuit-breaker and short-circuit
faults, the autoretry timer starts immediately. The timer
times out in 3.5s (typ) after which the sequencer initi-
ates a load-probe test and if successful, initiates a nor-
mal power-up GATE cycle.
When the MAX5938L enters fault management it
remains in this condition indefinitely until the power is
recycled or until OFF is brought below 1.25V (no time
dependence) and ON is brought below 1.125V for
1.5ms (typ). In addition, if the MAX5938L enters fault
management due to an overvoltage fault, the overvolt-
age fault must be removed. When the last of these con-
ditions has been met, the sequencer initiates a load-
probe test and if successful, a normal power-up GATE
cycle begins. A manual reset circuit as in Figure 2 can
be used to clear the latch.
The MAX5938 has a minimum circuit-breaker threshold
voltage of 50mV when CB_ADJ is connected to V
V
tor between CB_ADJ and V
-48V Hot-Swap Controller with V
CB
Autoretry Fault Management (MAX5938A)
90% of full enhancement,
full enhancement,
for more than 1.5ms.
Latched Fault Management (MAX5938L)
OUT
OUT
OUT
IN
is half V
V
exceeds the programmed overvoltage (OV) limit
CB
exceeds the V
exceeds the V
exceeds 74% of V
(mV) =
EE
SC
, which turns off the external MOSFET and
and can be increased by placing a resis-
1
x [R
/
2
______________________________________________________________________________________
x V
INT
Circuit-Breaker Threshold
SC
SC
CB
(kΩ) + R
No R
during full enhancement,
(mV) =
EE
for longer than 1.2ms during
CB
according to the following:
Fault Management
CB_ADJ
during GATE ramp at
1
/
2
SENSE
x I
CB_ADJ
(kΩ)]
(µA)
EE
, and Overvoltage Protection
. The
where I
precision, ±0.5%, 2kΩ resistor at CB_ADJ and R
is the external resistor between CB_ADJ and V
current source I
(increasing with temperature) to track the normalized
temperature coefficient of typical power MOSFETs.
The proper circuit-breaker threshold for an application
depends on the R
and the maximum current the load is expected to draw.
To avoid false fault indication and dropping of the load,
the designer must take into account the load response to
voltage ripples and noise from the backplane power sup-
ply as well as switching currents in the downstream DC-
DC converter that is loading the circuit. While the
circuit-breaker threshold has glitch rejection that ignores
ripples and noise lasting less than 1.2ms, the short-cir-
cuit detection is designed to respond very quickly (less
than 330ns) to a short circuit. For this reason, set V
and V
ripples, noise, and system current transients (see the
Setting the Circuit-Breaker and Short-Circuit Thresholds
section in the Applications Information).
Figure 8. Resetting the MAX5938L after a Fault Condition
Using a Push-Button Switch
CB
CB_ADJ
with an adequate margin to cover all possible
IN
V
= 50µA (typ at +25°C), R
IN
R4
R3
R2
R1
CB_ADJ
= (GND - V
DS(ON)
Step Immunity,
EE
OFF
ON
OV
V
GND
)
EE
of the external power MOSFET
is temperature-compensated
MAX5938
INT
is an internal
EE
CB_ADJ
. The
SC
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