ADM1191

Rev. 0 | Page 14 of 16

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 ALERTB 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.

ALERTB OUTPUT

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

This output can be used as an overcurrent flag by connecting it

to the general-purpose logic input of a controller. Under normal

operation, this output is pulled high (an external pull-up resistor

should be used because this is an open-drain pin). When an

overcurrent condition occurs, the ADM1191 pulls this output low.

P = VI

CONTROLLER

ADM1191

SENSE

VCC

SDA

SCL

SDA

SCL

GND

ALERTB

CLRB

CLRB

ADR

TIMER

3.15V TO 26V

SETV

ALERTB

Figure 25. Using the ALERTB Output as an Interrupt

SETV PIN

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

trips the ALERTB 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, then the output of the comparator asserts. By

driving a different voltage onto the SETV pin, the ADM1191

detects an overcurrent condition at a different current level,

with a gain of 18. See Figure 15 for an illustration of this

relationship.

ADM1191

SETV

ALERT

CURRENT

SENSE

AMPLIFIER

A

ALERT

APPLIED

VOLTAGE

SENSE

VCC

COMPARATOR

Figure 26. SETV Operation

KELVIN SENSE RESISTOR CONNECTION

When using a low value sense resistor for high current

measurement, the problem of parasitic series resistance can

arise. The lead resistance can be a substantial fraction of the

rated resistance, making the total resistance a function of lead

length. This problem can be avoided by using a Kelvin sense

connection. This type of connection separates the current path

through the resistor and the voltage drop across the resistor.

Figure 27 shows the correct way to connect the sense resistor

between the VCC pin and the SENSE pin of the ADM1191.

SENSE RESISTOR

KELVIN SENSE TRACES

VCC

SENSE

ADM1191

CURRENT

FLOW FROM

SUPPLY

CURRENT

FLOW TO

LOAD

Figure 27. Kelvin Sense Connections