MAX5938LEEE+【PDF 9/26 页】IC HOT-SWAP CTRLR -48V 16-QSOP

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Sheet目录43

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-48V Hot-Swap Controller with V

Step Immunity,

No R

SENSE

, and Overvoltage Protection

_______________________________________________________________________________________ 9

Figure 3. Load-Probe Test During Initial Power-Up

40ms/div

LOAD

= 100礔

= 75k&

20V/div

OUT

200mV/div

20V/div

GND

Figure 2. GATE Voltage Clamp During Power-Up

20V/div

GATE

1V/div

4ms/div

= 100礔

LP is shut off. The MAX5938A times out for 16 x t

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

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 52礎 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

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

) ramps to below 74% of the programmed circuit-

breaker threshold voltage, V

. 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

(when

GATE reaches 90% of full enhancement), then a power-

up-to-fault-management fault has occurred). GATE is

rapidly pulled to V

, 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 MOSFETs R

DS(ON)

as the current-

sense resistance to detect excessive current through

Figure 4. MAX5938 Normal Startup (POL_SEL = Floating)

50V/div

PGOOD

50V/div

40ms/div

GATE

10V/div

OUT

50V/div

2A/div

Figure 5. MAX5938 Startup into Fault Condition (POL_SEL =

Floating)

50V/div

PGOOD

50V/div

40ms/div

GATE

10V/div

OUT

50V/div

2A/div

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