Datasheet

capacitance (gate-to-drain) would pull up and turn on
the MOSFET gate when the MOSFET drain is rapidly
pulled up by the V
IN
step during backplane contact.
The MAX5938 GATE clamp can overcome the gate-to-
drain capacitance of large power MOSFETs with added
slew-rate control (C
SLEW
) capacitors while eliminating
the need for additional gate-to-source capacitance.
The MAX5938 keeps the MOSFET off indefinitely if the
supply voltage is below the user-set ON and OFF
thresholds, if the supply voltage is above the user-set
overvoltage (OV) threshold, or if a short circuit (user-
defined) is detected in the load connected to the drain
of the power MOSFET.
The MAX5938 conducts a load-probe test after contact
transients from the hot plug-in have settled. This follows
the MAX5938 power-up (when the ON, OFF, and OV
conditions have been met for 220ms (t
LP
)) and prior to
the turn-on of the power MOSFET. This test pulls a user-
programmable current through the load (1A, max) for up
to 220ms (t
LP
) and tests for a voltage of 200mV across
the load at V
OUT
(Figure 3). This current is set by an
external resistor, R
LP
(Figure 17) between V
OUT
and LP.
When the voltage across the load exceeds 200mV, the
test is truncated and the GATE turn-on sequence is start-
ed. If at the end of the 200ms (t
LP
) test period the volt-
age across the load has not reached 200mV, the load is
assumed to be shorted and the current to the load from
Figure 1. Functional Diagram
10V REG
AND
5V REG
PGOOD
POLARITY
LOGIC
ON, OFF,
AND OV
LOGIC CONTROL
BANDGAP
REF
V
BG
10µA
FAULT
DETECTION
SEQUENCER
CONTROLLER
TIMER
GATE
CONTROL
LOAD-PROBE
TEST
V
SC
, V
CB
, AND
75% OF V
CB
COMPARATORS
STEP
50µA TEMP
COMPENSATED
CURRENT SOURCE
V
BG
(1.25V)
+5V
+10V
52µA
2V AND
15V
CLAMP
PGOOD
LOGIC
MAX5938
PGOOD
V
OUT
GATE
LP
R
LOAD
C
LOAD
ON
GND
STEP_MON
V
EE
GND
V
EE
R
INT
2kΩ
CB_ADJ
PG
OV
PG
OFF
OV
POL_SEL
MAX5938
-48V Hot-Swap Controller with V
IN
Step Immunity,
No R
SENSE
, and Overvoltage Protection
8 _______________________________________________________________________________________