X80070 Datasheet, PDF (11/14 Pages) Intersil Corporation – Hot Swap Controller with Advanced Fault Protection and Voltage Refulator Output

X80070, X80071, X80072, X80073
Figure 9. Overvoltage/Undervoltage for Primary and
Battery Backup
R1
450K
V_UV/OV
R2
25K
-48V
BATT-ON
-
+
V_{OV Voltage}
Reference
-
+
V_{UV1 Voltage}
Reference
-
+
V_{UV2 Voltage}
Reference
To Gate
Control
To Gate
Control
2:1
Mux
Overcurrent Protection (Circuit Breaker Function)
The X80070 overcurrent circuit provides the following functions:
– Overcurrent shut-down of the power FET and external
power good indicators.
– Noise filtering of the current monitor input.
– Relaxed overcurrent limits for initial board insertion.
– Overcurrent recovery retry operation.
Overcurrent shut-down
A sense resistor, placed in the supply path between V_EE and
SENSE (see Figure 6) generates a voltage internal to the
X80070. When this voltage exceeds 50mV, an overcurrent
condition exists and an internal “circuit breaker” trips, turning
off the gate drive to the external FET. The actual overcurrent
level is dependent on the value of the current sense resistor.
For example a 20mΩ sense resistor sets the overcurrent level
to 2.5A.
As shown in Figure 10, this overcurrent circuit block contains a
resistor ladder, a comparator, a noise filter and a voltage
reference to monitor for overcurrent conditions.
The overcurrent voltage threshold (V_OC) is 50mV. This can be
factory set, by special order, to any setting between 30mV and
100mV.
If an overcurrent condition is detected, the GATE output is shut
down and the power good indicator goes inactive.
Overcurrent during insertion
Insertion is defined as the first plug-in of the board to the
backplane. In this case, the X80070 is initially fully powered off
prior to the hot plug connection to the main supply. This
condition is different from a situation where the main supply has
temporarily failed resulting in a partial recycle of the power. This
second condition will be referred to as a power cycle.
During insertion, the board can experience high levels of
current for short periods of time as power supply capacitors
charge up on the power bus. To prevent the overcurrent sensor
from turning off the FET inadvertently, the X80070 has the
ability to allow more current to flow through the power FET and
the sense resistor for a short period of time until the FET turns
on and the PWRGD signal goes active.
In the X80070, 150mV is allowed across sense resistor during
insertion (7.5A assuming a 20mW resistor). This provides a
mechanism to reduce insertion issues associated with huge
current surges. Insertion currents of 1X, 2X, or 4X are also
available. Please contact Intersil for these factory options.
After the PWRGD signal is asserted, the X80070 switches back
to the normal overcurrent setting.
Hardshort Protection - (Retry)
In the event on an overcurrent or hard short condition, the
X80070 includes a retry circuit. This circuit waits for 100ms,
then attempts to again turn on the FET. If the fault condition still
exists, the FET turns off and the sequence repeats. For
versions X80070 and X80072, this process continues indefinely
until the overcurrent condition does not exist. For the X80071
and X80073, this process repeats five times only, then will keep
the FET off and set the FAR pin active. After FAR is asserted, it
can be cleared using the master reset pin, MR, or cycling the
power-on V_DD. When using the MR pin, the FAR output is
cleared upon MR assertion.
If an overcurrent condition does not occur on any retry, the gate
pin will proceed to open at the user defined slew rate.
Figure 10. Overcurrent Detection/Short Circuit
Protection.
Voltage
Reference
38R
–
3R
+
5us
noise
filtering
-48V
R_Sense
Overcurrent Event
Gate
Control
Block
Overcurrent/
Short-Circuit
Retry Logic
RETRY
Delay
Overcurrent noise filter
The X80070 has a noise (low pass) filter built into the
overcurrent comparator. The comparator will thus require
the current spikes to exceed the overcurrent limit for more
than 5µs.
11
FN8150.0
March 15, 2005