+72V SOT23 Simple Swapper Hot-Swap

Controllers

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5

Detailed Description

The MAX5902/MAX5903 are integrated hot-swap con-

troller ICs contained in 6-pin SOT23 packages. They

allow a board to be safely hot-plugged into a live back-

plane without causing a glitch on the power-supply rail.

They are well suited for +48V power systems 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°C. 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

MAX5902L/MAX5903L turn off the MOSFET, discon-

ON/OFF

GND

GND

GND

3V

MAX5902

MAX5903

828k

Ω

*900k

Ω

34.5k

Ω

1k

Ω

GATE

DRAIN

CONTROL

LOGIC

PGOOD

(PGOOD)

( ) ARE FOR THE MAX5903 ONLY

* RELATIVE TOLERANCE

±1%, ABSOLUTE TOLERANCE ±50% (TYP)

*650k

Ω

*

*

Figure 1. Functional Block Diagram

Pin Description

PIN

MAX5902

MAX5903

NAME

FUNCTION

11

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

2

2

DRAIN

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

possible to the MOSFET’s drain and use wide circuit traces to assure good thermal

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

3

3

GATE

Gate Drive Output for External P-Channel MOSFET

4

4

GND

Ground Connection

5

—

PGOOD

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

referenced to GND.

—

5

PGOOD

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

referenced to GND.

6

6

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

Ω resistor. (See Figure 1.) (See Undervoltage Lockout in the Applications

section of this data sheet.)