+60V Simple Swapper Hot-Swap Switch

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9

Digital Logic

VDIG is the input supply for the internal logic circuitry.

The logic input thresholds of EN, LATCH, and ZC_EN

are CMOS compatible and are determined by the volt-

age at VDIG, which can range from 1.65V to 5.5V. The

POK and FAULT outputs are open-drain. VDIG and all

logic inputs and outputs are referenced to DGND.

DGND is not connected to AGND_S internally and must

be connected externally at a single point in the system

to AGND_S. The maximum allowable difference in the

voltage between DGND and AGND is

±4V.

Enable (EN)

EN is a logic input to enable MAX5923. Bringing EN low

halts all operations and turns off the internal power

MOSFET. When EN is high and the input voltage is

above the UVLO threshold, the MAX5923 begins oper-

ating. Enable is also used to unlatch the part after a

latched fault condition. This is done by toggling EN low

and high again after a fault condition.

Overcurrent Protection

The MAX5923 provides a sophisticated overcurrent pro-

tection circuitry to ensure the robust operation under out-

put current transient and current-fault conditions. The

current protection circuitry employs a Constant Current

Limit, a Current Foldback, and an Overcurrent Timeout.

Constant Current Limit

lates the current through the power MOSFET as neces-

the OUT pin works like a constant current source, limit-

limit fault is generated and the power MOSFET is

turned off (see the Overcurrent Timeout and Fault

Management section).

Current Foldback

While in current-limit condition, the voltage at the OUT pin

drops. As the load resistance reduces (more loading), the

output voltage reduces accordingly to maintain a con-

stant load current. The power dissipation in the power

drops lower, more power is dissipated across the power

MOSFET. To reduce this power dissipation, the MAX5923

offers a current foldback feature where it linearly reduces

trates this current foldback limit behavior.

Overcurrent Timeout

The MAX5923 keeps track of the time it is in current limit.

An internal digital counter begins incrementing its count

to zero if the current falls back below the current limit.

When the cumulative count reaches 60, an overcurrent

fault is generated. After an overcurrent fault condition, the

switch is turned off and the FAULT signal goes low. This

overcurrent timeout enables the MAX5923 to operate in a

periodic overcurrent condition without causing a fault.

See Figure 3 for an example of periodic overcurrent con-

dition without causing a fault.

(2V)

(18V)

Figure 2. Current Foldback Characteristic

MAX5923

IN

UVLO

AGND

R1

R2

Figure 1. Setting Undervoltage Lockout with an External

Resistive Divider