Datasheet

MAX5938
-48V Hot-Swap Controller with V
IN
Step Immunity,
No R
SENSE
, and Overvoltage Protection
_______________________________________________________________________________________ 9
Figure 3. Load-Probe Test During Initial Power-Up
40ms/div
C
LOAD
= 100µF
R
LP
= 75kΩ
V
EE
20V/div
V
OUT
200mV/div
V
LP
20V/div
GND
GND
GND
Figure 2. GATE Voltage Clamp During Power-Up
V
IN
20V/div
V
GATE
1V/div
4ms/div
C
IN
= 100µF
LP is shut off. The MAX5938A times out for 16 x t
LP
then
retry the load-probe test. The MAX5938L latches the fault
condition indefinitely until ON and OFF are cycled low for
1.5ms or the power is recycled. See the Applications
Information for recommendations on selecting R
LP
to set
the load-probe current level.
Upon successful completion of the load-probe test, the
MAX5938 enters the power-up GATE cycle and begins
ramping the GATE voltage with a 52µA current source.
This current source is restricted if V
OUT
begins to ramp
down faster than the default 9V/ms slew rate. The V
OUT
slew rate can be reduced to below 9V/ms by adding
C
SLEW
from GATE to V
OUT
. Charging up GATE
enhances the power MOSFET in a controlled manner
and ramping V
OUT
at a user-settable rate controls the
inrush current from the backplane. The MAX5938 con-
tinues to charge up the GATE until one of two events
occurs: a normal power-up GATE cycle is completed or
a power-up-to-fault-management fault is detected (see
the GATE Cycles section in Appendix A). In a normal
power-up GATE cycle, the voltage at V
OUT
(referenced
to V
EE
) ramps to below 74% of the programmed circuit-
breaker threshold voltage, V
CB
. At this time, the remain-
ing GATE voltage is rapidly pulled up to full
enhancement. PGOOD is asserted 1.26ms after GATE
is fully enhanced (see Figure 4). If the voltage at V
OUT
remains above 74% of the programmed V
CB
(when
GATE reaches 90% of full enhancement), then a power-
up-to-fault-management fault has occurred). GATE is
rapidly pulled to V
EE
, turning off the power MOSFET
and disconnecting the load. PGOOD remains deassert-
ed and the MAX5938 enters the fault management
mode (Figure 5).
When the power MOSFET is fully enhanced, the
MAX5938 monitors the drain voltage (V
OUT
) for circuit-
breaker and short-circuit faults. The MAX5938 makes
use of the power MOSFET’s R
DS(ON)
as the current-
sense resistance to detect excessive current through
Figure 4. MAX5938 Normal Startup (POL_SEL = Floating)
V
IN
50V/div
V
PGOOD
50V/div
40ms/div
V
GATE
10V/div
V
OUT
50V/div
I
IN
2A/div
Figure 5. MAX5938 Startup into Fault Condition (POL_SEL =
Floating)
V
IN
50V/div
V
PGOOD
50V/div
40ms/div
V
GATE
10V/div
V
OUT
50V/div
I
IN
2A/div