ADM1192

Rev. 0 | Page 15 of 20

Table 15. Status Byte Operations

Bit

Name

Function

0

ADC_OC

An ADC-based overcurrent comparison has been detected on the last three conversions.

1

ADC_ALERT

An ADC-based overcurrent trip has occurred, which has caused the alert. Cleared by writing to Bit 4 of the ALERT_EN

register.

2

OC

An overcurrent condition is present (that is, the output of the current sense amplifier is greater than the voltage on the

SETV input).

3

OC_ALERT

An overcurrent condition has caused the ALERT block to latch a fault, and the ALERT output has asserted. Cleared by

writing to Bit 4 of the ALERT_EN register.

4

OFF_STATUS

Set to 1 by writing to the SWOFF bit of the CONTROL register.

5

OFF_ALERT

An alert has been caused by the SWOFF bit. Cleared by writing to Bit 4 of the ALERT_EN register.

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. Under 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

ALERT

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 at turn-on. Note that if a current fault

occurs at any point in 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