MAX5903LAETT+T【PDF 5/14 页】IC HOT-SWAP CONTROLLER 6-TDFN

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+72V, SOT23/TDFN, Simple Swapper Hot-Swap

Controllers

_______________________________________________________________________________________ 5

Detailed Description

The MAX5902/MAX5903 are integrated hot-swap con-

troller ICs contained in 6-pin SOT23 and TDFN pack-

ages. They allow a board to be safely hot-plugged into

a live backplane without causing a glitch on the power-

supply rail. They are well suited for +48V power sys-

tems allowing cost-effective, simple, and compact

design. The MAX5902/MAX5903 operate from +9V to

+72V to cover a wide range of end equipment hot-swap

needs. They require only an external p-channel power

MOSFET to provide hot-swap control. Figure 1 shows a

functional block diagram of the MAX5902/MAX5903.

The MAX5902/MAX5903 controls an external p-channel

power MOSFET placed in the positive power-supply

pathway. When power is first applied, the MAX5902/

MAX5903 keep the MOSFET turned off. The

MAX5902/MAX5903 hold the MOSFET off indefinitely if

ON/OFF is held low, if the supply voltage is below the

undervoltage lockout level, or if the die temperature

exceeds +125癈. If none of these conditions exist for

150ms (typ), the MAX5902/MAX5903 begin to gradually

turn on the MOSFET. During this turn-on phase, the

MAX5902/MAX5903 slowly enhance the MOSFET,

allowing the voltage on the load, i.e. the drain of the

MOSFET, to rise at a rate of 9V/ms (typ). The inrush cur-

rent to the load is thus limited to a level proportional to

the load capacitance, and the constant slew rate. After

the MOSFET is fully enhanced, and the load voltage is

settled to its final value, the MAX5902A/ MAX5903A and

MAX5902L/MAX5903L monitor the voltage drop across

the MOSFET. If the voltage drop exceeds the circuit-

breaker threshold the MAX5902A/MAX5903A and

ON/OFF

GND

MAX5902

MAX5903

828k&

*900k&

34.5k&

1k&

GATE

DRAIN

CONTROL

LOGIC

PGOOD

(PGOOD)

( ) ARE FOR THE MAX5903 ONLY

* RELATIVE TOLERANCE ?%, ABSOLUTE TOLERANCE ?0% (TYP)

*650k&

Figure 1. Functional Block Diagram

Pin Description

MAX

MAX5903

NAME

FUNCTION

Positive Supply Voltage Input and External p-Channel MOSFET Source Connection

DRAIN

Drain Sense Input for External p-Channel MOSFET. Connect DRAIN as close as

possible to the MOSFETs drain and use wide circuit traces to assure good thermal

coupling between the MAX5902/MAX5903 and the MOSFET. See Layout Guidelines

Section.

GATE

Gate Drive Output for External p-Channel MOSFET

GND

Ground Connection

PGOOD

Power-Good Output. PGOOD is an n-channel, open-drain, active-low output,

referenced to GND.

PGOOD

Power-Good Output. PGOOD is an n-channel, open-drain, active-high output,

referenced to GND.

ON/OFF

ON/OFF Control Input. ON/OFF is referenced to GND. Drive ON/OFF above 1.38V or

leave unconnected to enable the device. Drive ON/OFF below 1V to disable the device.

ON/OFF is also used to adjust the UVLO threshold. Internally clamped to nominally 3V

through a 1k& resistor (See Figure 1). (See the Undervoltage Lockout section in the

Applications Information.)

Exposed Pad (TDFN only). Connect to GND.

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