max5938 Maxim Integrated Products, Inc., max5938 Datasheet - Page 20

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

-48V Hot-Swap Controller with V
No R
trol are in the linear range. If this is an issue, an external
resistor, R
ommended to prevent possible oscillation. It should be as
small as possible, e.g., 5Ω to 10Ω, to avoid impacting the
MOSFET turn-off performance of the MAX5938.
To benefit from the temperature compensation designed
into the MAX5938, the part should be placed as close as
possible to the power MOSFET that it is controlling. The
V
source pin of the power MOSFET and they should share
a wide trace. A common top layer plane would service
both the thermal and electrical requirements. The load-
probe current must be taken into account. If this current
is high, the layout traces and current-limiting resistor
must be sized appropriately. Stray inductance must be
minimized in the traces of the overall layout of the hot-
swap controller, the power MOSFET and the load capac-
itor. Starting from the board contacts, all high-current
traces should be short, wide, and direct. The potentially
high pulse current pins of the MAX5938 are GATE (when
pulling GATE low), load probe, and V
nature of the hot-swap requirement no decoupling
capacitor is recommended for the MAX5938. Because
there is no decoupling capacitor, stray inductance may
result in excessive ringing at the GND pin during power-
up or during very rapid V
ined in every application design since ringing at the
GND pin may exceed the absolute maximum supply rat-
ing for the part.
During hot plug-in/unplug and fast V
inductance in the power path may cause voltage ring-
ing above the normal input DC value, which may
exceed the absolute maximum supply rating. An input
transient such as that caused by lightning can also put
a severe transient peak voltage on the input rail. The
following techniques are recommended to reduce the
effect of transients:
1) Minimize stray inductance in the power path using
2) Add a high-frequency (ceramic) bypass capacitor
3) Add a 1kΩ resistor in series with the MAX5938’s
20
EE
wide traces and minimize loop area including the
power traces and the return ground path.
on the backplane as close as possible to the plug-
in connector (Figure 20).
GND pin and a 0.1µF capacitor from GND to V
limit transient current going into this pin.
pin of the MAX5938 should be placed close to the
______________________________________________________________________________________
GATE
SENSE
, in series with gate of the MOSFET is rec-
Input Transient Protection
IN
, and Overvoltage Protection
steps. This should be exam-
Layout Guidelines
EE
. Because of the
IN
steps, stray
EE
to
The power-up GATE cycle, step GATE cycle, and the OV
GATE cycle are quite similar but have distinct differ-
ences. Understanding these differences may clarify
application issues.
The power-up GATE cycle occurs during the initial
power-up of the MAX5938 and the associated power
MOSFET and load. The power-up GATE cycle can
result in full enhancement or in a fault (all voltages are
relative to V
Power-Up-to-Full-Enhancement Fault:
1) At the beginning of the power-up sequence to the
2) When GATE reaches the gate threshold voltage of
3) When V
Figure 20. Protecting the MAX5938 Input from High-Voltage
Transients
1µF
start of the power-up GATE cycle, the GATE is held
at V
load-probe test, GATE is held at V
350µs and then is allowed to float for 650µs. At this
point, the GATE begins to ramp with 52µA charging
the gate of the power MOSFET. [GATE turn-on]
the power MOSFET, V
toward V
rapidly pulled to full enhancement and the power-
up GATE cycle is complete. 1.26ms after GATE is
pulled to full enhancement, PGOOD asserts. [Full
enhancement]
BACKPLANE
0.1µF
EE
48V
. Following a successful completion of the
EE
OUT
EE
).
IN
. [V
ramps below 74% V
OUT
Step Immunity,
ramp]
GATE Cycle During Power-Up
OUT
0.1µF
begins to ramp down
ON
OV
OFF
STEP_MON
PLUG-IN CARD
EE
Appendix A
CB
GND
GATE Cycles
V
EE
for an additional
PGOOD
1kΩ
, the GATE is
100kΩ