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AN-805
APPLICATION NOTE
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INTRODUCTION
The ADM1073 –48 V hot swap controller accurately
limits the current drawn from a supply by dynamically
controlling the GATE voltage on an external N-channel
FET placed in the path of that supply. An internal sense
amplifier detects the voltage across a sense resistor con-
nected between its VEE and SENSE pins. This voltage
level gives an indication of the load current level. The
sense amplifier has a preset control loop threshold of
100 mV (3%). This means the current control loop will
regulate the load current when a voltage of 100 mV is
detected across the sense resistor. In this way the value
of the sense resistor sets the current level that causes
the loop to regulate. 100 mV divided by R
SENSE
yields the
current value at which the sense resistor causes the loop
to regulate.
Altering the ADM1073 Current Limit Level
by Alan Moloney
In addition to the 100 mV threshold, there is a separate
circuit breaker threshold below this. It is nominally
90 mV (minimum 86 mV). If the load current is at a level
that exceeds the circuit breaker level then the internal
counter begins timing the event as a fault. Note that the
device does not begin to regulate current until the cur-
rent limit control loop threshold is reached.
Table I shows the current limit levels for different values
of sense resistor.
I
LOAD(MAX)
is the maximum load current level that may
trigger a current fault. This corresponds to a voltage of
86 mV across the sense resistor.
I
LIMIT(MIN)
and I
LIMIT(MAX)
are the minimum and maximum
load current levels at which the current limit loop will
regulate. These correspond to voltages of 97 mV and
103 mV across the sense resistor, respectively.
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Figure 1. ADM1073 Application Diagram
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