12V/5V Hot-Plug Switch

7

Detailed Description

The MAX34561 has hot-plug controls for both +12V and

+5V power rails. The circuitry for the +12V and +5V con-

trols are independent of each other and can be treated

as two separate hot-plug switches, even though the GND

pin is common between the two switches. The sections

that follow are written from the +12V circuit perspective,

but also apply for the +5V switch control.

The device begins to operate when the supply voltage

circuit and TIMER12 (TIMER5) become active. Once the

device has been enabled, a gate voltage is applied to

the corresponding power MOSFET, allowing current to

The speed of the output-voltage ramp is controlled by

the capacitance placed at the VRAMP12 (VRAMP5) pin.

The load current is continuously monitored during the

current exceeds the current limit that is set by the exter-

nal resistance at ILIM12 (ILIM5), the gate voltage of the

corresponding power MOSFET is decreased, reducing

the output current to the set current limit.

Current is limited by the device comparing the volt-

age difference between LOAD12 (LOAD5) and ILIM12

(ILIM5) to an internal reference voltage. If the output cur-

resistor, the gate voltage of the corresponding power

MOSFET is decreased, which reduces the output current

to the load.

When the output power is initially ramping up, the current

short on initial power-up.

The device acts as a fuse and automatically disables the

current flowing to the load when the temperature of the

power corresponding MOSFET has exceeded the shut-

Enable/Timer

The voltage level of TIMER12 (TIMER5) is compared to

an internal source (see the Functional Diagram). When

puts a low level. This then turns on the voltage ramp

circuit, enabling the device’s output. TIMER12 (TIMER5)

can be configured into one of four different modes of

operation as listed in Table 1. TIMER12 (TIMER5) pin

was designed to work with most logic families. TIMER12

to drive TIMER12 (TIMER5) be tested to ensure proper

operation.

Pin Description (continued)

Table 1. TIMER_ Pin Modes

PIN

NAME

FUNCTION

22

ARD5

5V Autoretry Disable. Connect this pin to GND to disable automatic retry functionality; the device

latches off during an overtemperature fault. Leave this pin open to enable automatic retry function.

side is not used, connect this pin to GND.

23

VRAMP5

5V Voltage Ramp Control. A capacitor connected to this pin determines the voltage ramp of the

24

TIMER5

5V Enable Delay Control. A capacitor connected to this pin determines the enable delay according

—

EP

Exposed Pad. Connect to ground. The EP must be soldered to ground for proper thermal and elec-

trical operation.

OPERATION MODE

TIMER PIN SETUP

Automatic Enable

No connection to TIMER12

(TIMER5)

Delayed Automatic Enable

to TIMER12 (TIMER5)

Enable/Disable

Open-collector device

Enable with Delay/Disable

Open-collector device and