ADM1192 Data Sheet
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. This pin is configured by default to trigger the SETV
threshold at power-up.
R
SENSE
P = VI
CONTROLLER
ADM1192
SENSEVCC
SDA
SCL
SDA
SCL
GND
ALERT
CLRB
CLRB
ADR
TIMER
3.15V TO 26V
SETV
INTERRUPT
05754-013
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 ALERT 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.
R
SENSE
P-CHANNEL FET
P = VI
CONTROLLER
ADM1192
SENSE
VCC
SDA
SCL
SDA
SCL
GND
ALERT
CLRB
CLRB
ADR
TIMER
3.15V TO 26V
SETV
05754-014
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. The 100 mV ADC
full-scale sense voltage corresponds to 1.8 V on the SETV pin.
See Figure 12 for an illustration of this relationship.
ADM1192
SETV
1.3V
ALERT
CURRENT
SENSE
AMPLIFIER
A
ALERT
60µA
R
SENSE
I
LOAD
APPLIED
VOLTAGE
SENSE
VCC
TIMER
COMPARATOR
05754-015
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 62 μA charging current. When the voltage on the TIMER
capacitor reaches 1.3 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.
KELVIN SENSE RESISTOR CONNECTION
When using a low value sense resistor for high current
measurement, the problem of parasitic series resistance can arise.
The pad and solder resistance can be a substantial fraction of the
rated resistance, making the total resistance larger than expected.
This error problem can be largely avoided by using a Kelvin
sense connection. This type of connection separates the high
current path through the resistor and the voltage drop across the
resistor. A four pad resistor may be used or a split pad layout can be
used with a two pad sense resistor to achieve Kelvin sensing.
Rev. D | Page 16 of 20
