ADM1192

Rev. B | Page 16 of 20

APPLICATIONS INFORMATION

ALERT OUTPUT

The ALERT output is an open-drain pin with 30 V tolerance.

There are two uses for this output.

Overcurrent Flag

The ALERT pin can be connected to the general-purpose logic

input of a controller. During normal operation, the ADM1192

drives this output low. When an overcurrent condition occurs,

the output asserts high. An external pull-up resistor should

be used.

P = VI

CONTROLLER

ADM1192

SENSE

VCC

SDA

SCL

SDA

SCL

GND

ALERT

CLRB

CLRB

ADR

TIMER

3.15V TO 26V

SETV

INTERRUPT

Figure 27. Using the ALERT Output as an Interrupt

Implementing a Basic Hot Swap Circuit

A basic P-channel FET hot swap circuit can be created. The

ALERT output should be connected to the GATE pin of a P-

channel FET connected in series with the power path. A pull-up

from GATE to source ensures that the P-channel FET GATE is

pulled up and the device held off as soon as power is applied.

When the ADM1192 powers up, the GATE is pulled low by the

ALERT output. A capacitor on the TIMER pin determines the

slew rate of the GATE pin at startup. Note that if a current fault

occurs during the operation, the ALERT output asserts high,

turning off the P-channel FET.

P-CHANNEL FET

P = VI

CONTROLLER

ADM1192

SENSE

VCC

SDA

SCL

SDA

SCL

GND

ALERT

CLRB

CLRB

ADR

TIMER

3.15V TO 26V

SETV

Figure 28. P-Channel FET Hot Swap Implementation

SETV PIN

The SETV pin allows the user to adjust the current level that

trips the ALERT output. The output of the current sense amplifier

is compared with the voltage driven onto the SETV pin. If the

current sense amplifier output is higher than the SETV voltage,

the output of the comparator asserts. By driving a different voltage

onto the SETV pin, the ADM1192 detects an overcurrent condition

at a different current level, with a gain of 18. See Figure 12 for

an illustration of this relationship.

ADM1192

SETV

1.3V

ALERT

CURRENT

SENSE

AMPLIFIER

A

ALERT

60µA

APPLIED

VOLTAGE

SENSE

VCC

TIMER

COMPARATOR

Figure 29. SETV Operation

When the output of the SETV comparator asserts, this tells the

ALERT block to begin charging the external TIMER capacitor

with a 60 μA charging current. When the voltage on the TIMER

capacitor reaches 1 V, the charging cycle is complete. The ALERT

output then asserts (goes high). Different values of TIMER

capacitor generate different time delays between current faults

occurring and the ALERT output asserting. When using the

ALERT output to implement a hot swap circuit, the TIMER

capacitor should be chosen to generate a large enough startup

delay to allow the maximum inrush current to completely

charge up the load without tripping an ALERT fault.