Preliminary Technical Data

ADM1177

Rev. PrD | Page 15 of 16

Table 14. Status Byte Operations

Bit

Name

Function

0

ADC_OC

An ADC based overcurrent comparison has been detected on the last 3 conversions

1

ADC_ALERT

An ADC based overcurrent trip has happened, which has caused the ALERT. Cleared by writing to bit 4 of the

ALERT_EN register.

2

HS_OC

The hotswap is off due to an analog overcurrent event. On parts which latch off, this will be the same as the HS_ALERT

status bit (if EN_HS_ALERT=1). On the retry parts this will indicate the current state—a 0 could indicate that the data

was read during a period when the device is retrying, or that it has successfully hotswapped by retrying after at least

one overcurrent timeout.

3

HS_ALERT

The hotswapper has failed since the last time this was reset. Cleared by writing to bit 4 of the ALERT_EN register.

4

OFF_STATUS

The state of the ON pin. Set to 1 if the input pin is de-asserted. Can also be set to 1 by writing to the SWOFF bit of the

CONTROL register.

5

OFF_ALERT

An alert has been caused either by the ON pin or the SWOFF bit. Cleared by writing to bit 4 of the ALERT_EN register.

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 15 below shows the correct way to connect the sense

resistor between the VCC and SENSE pins of the ADM1177.

SENSE RESISTOR

KELVIN SENSE TRACES

CURRENT

FLOW TO

LOAD

CURRENT

FLOW FROM

SUPPLY

SENSE

ADM1177

Figure 15. Kelvin Sense Connections