Rainbow-electronics MAX5937 Bedienungsanleitung PDF herunterladen (Seite 7)

MAX5936/MAX5937

-48V Hot-Swap Controllers with V

Step Immunity and No R

SENSE

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Detailed Description

The MAX5936/MAX5937 hot-swap controllers incorpo-

rate overcurrent fault management and are intended for

negative-supply-rail applications. The MAX5936/

MAX5937 eliminate the need for an external R

SENSE

and include V

input-step protection and load probe,

which prevents powering up into a shorted load. They

are intended for negative 48V telecom power systems

where low cost, flexibility, multifault management, and

compact size are required. The MAX5936/MAX5937 are

ideal for the widest range of systems from those

requiring low current with small MOSFETs to high-

current systems requiring large power MOSFETs and

low on-resistance.

The MAX5936/MAX5937 control an external n-channel

power MOSFET placed in the negative supply path of

an external load. When no power is applied, the GATE

output of the MAX5936/MAX5937 clamps the V

of the

MOSFET to 2V, keeping the MOSFET turned off. When

power is applied to the MAX5936/MAX5937, the 2V

clamp at the GATE output is replaced by a strong pull-

down device pulling GATE to V

and the V

of the

MOSFET to 0V. As shown in Figure 2, this transition

enables the MAX5936/MAX5937 to keep the power

MOSFET continually off during the board insertion

phase when the circuit board first makes contact with

the backplane. Without this clamp, the GATE output of

a powered-down controller would be floating and the

MOSFET reverse transfer capacitance (gate-to-drain)

would pull up and turn on the MOSFET gate when the

MOSFET drain is rapidly pulled up by the V

step dur-

ing backplane contact. The MAX5936/MAX5937 GATE

clamp can overcome the gate-to-drain capacitance of

large power MOSFETs with added slew-rate control

SLEW

) capacitors while eliminating the need for addi-

tional gate-to-source capacitance. The MAX5936/

MAX5937 will keep the MOSFET off indefinitely if the

supply voltage is below the user-set UVLO threshold or

if a short circuit is detected in the load connected to the

drain of the power MOSFET.

MAX5936

MAX5937

NAME FUNCTION

11GND Ground. The high-supply connection for a negative-rail hot-swap controller.

22UVLO

Undervoltage Lockout Input, On/Off Control. Referenced to V

. Drive UVLO above the

1.25V rising threshold to turn on the device. To turn off the device, drive UVLO below the

1.125V falling threshold for the 1.5ms glitch rejection period. Leave UVLO disconnected for

the default 31V undervoltage lockout threshold. Cycle UVLO to unlatch the MAX5936L/

MAX5937L after a fault.

STEP_MON

Input Voltage Step Monitor. 1.25V voltage threshold referenced to V

. Connect a resistor

between STEP_MON and V

to set the step sensitivity. Connect a capacitor from GND to

STEP_MON to adjust the step response relative to a step increase at V

to eliminate false

circuit-breaker and short-circuit faults. Connect to V

to disable the step immunity function

(see the Selecting Resistor and Capacitor Values for Step Monitor section in the

Applications Information).

44V

Negative Input Voltage

55LP

Load-Probe Detect. Connect a resistor from LP to V

OUT

to set the load-probe test current.

Limit load-probe test current to 1A. Connect to V

to disable the load-probe function.

66GATE Gate-Drive Output. Connect to the gate of the external n-channel MOSFET.

77V

OUT

Output Voltage Sense. V

OUT

is the negative rail of the load. Connect to the drain of the

external n-channel MOSFET.

8—PGOOD

Power-Good, Active-Low, Open-Drain Output. Referenced to V

OUT

. PGOOD asserts low

when V

OUT

is within the limits and there is no fault.

—8PGOOD

Power-Good, Active-High, Open-Drain Output. Referenced to V

OUT

. PGOOD asserts high

when V

OUT

is within limits and there is no fault.

Pin Description

1 2 3 4 5 6 7 8 9 10 11 12 ... 22 23

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