X80010 Datasheet, PDF (16/25 Pages) Intersil Corporation – Penta-Power Sequence Controller with Hot swap and System Management

X80010, X80011, X80012, X80013
Overcurrent Protection (Circuit Breaker Function)
The X80010 over-current circuit provides the following
functions:
- Over-current shut-down of the power FET and external
power good indicators.
- Noise filtering of the current monitor input.
- Relaxed over-current limits for initial board insertion.
- Over-current recovery retry operation.
A sense resistor, placed in the supply path between V_EE and
SENSE (see Figure 30) generates a voltage internal to the
X80010. When this voltage exceeds 50mV an over current
condition exists and an internal “circuit breaker” trips, turning
off the gate drive to the external FET. The actual over-
current level is dependent on the value of the current sense
resistor. For example a 20mΩ sense resistor sets the over-
current level to 2.5A.
Intersil’s X80010 provides a safety mechanism during
insertion of the board into the back plane. During insertion of
the board into the backplane large currents may be induced.
In order to prevent premature shut down, the overcurrent
detect circuit of the X80010 allows up to 3 times the standard
overcurrent setting during insertion.
After the PWRGD signal is asserted, the X80010 switches
back to the normal overcurrent setting. The over-current
threshold voltage during insertion is 150mV.
After the Power FET turns off due to an over-current
condition, a retry circuit turns the FET back on after a delay
of 100ms. If the over-current condition remains, the FET
again turns off. For the X80010 and X80012, this sequence
repeats indefinitely until the over-current condition is
released. For the X80011 and X80013, the X80010 retries
five times, then, sets an output signal, FAR, to indicate a
failure after retry.
Over-current shut-down
As shown in Figure 35, this circuit block contains a resistor
divider, a comparator, a noise filter and a voltage reference
to monitor for over-current conditions.
Voltage
Reference
38R
3R
–
+
5µs
noise
filtering
Gate
Control
Block
Overcurrent/
Short-Circuit
Retry Logic
RETRY
Delay
-48V
R_Sense
Overcurrent Event
FIGURE 35. OVERCURRENT DETECTION/SHORT CIRCUIT
PROTECTION
The overcurrent voltage threshold (V_OC) is 50mV. This can
be factory set, by special order, to any setting between
30mV and 100mV. V_OC is the voltage between the SENSE
and V_EE pins and across the R_SENSE resistor. If the
selected sense resistor is 20mW, then 50mV corresponds to
an overcurrent of 2.5A.
If an over-current condition is detected, the GATE is turned
off and all power good indicators go inactive.
Overcurrent Noise Filter
The X80010 has a noise (low pass) filter built into the over-
current comparator. The comparator will thus require the
current spikes to exceed the overcurrent limit for more than
5µs.
Overcurrent During Insertion
Insertion is defined as the first plug-in of the board to the
backplane. In this case, the X80010 is initially fully powered
off prior to the hot plug connection to the mains supply. This
condition is different from a situation where the mains 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 over-current
sensor from turning off the FET inadvertently, the X80010
has the ability to allow more current to flow through the
powerFET and the sense resistor for a short period of time
until the FET turns on and the PWRGD signal goes active. In
the X80010, 150mV is allowed across sense resistor the
during insertion (10A assuming a 20mΩ resistor). This
provides a mechanism to reduce insertion issues associated
with huge current surges.
16
FN8149.0
January 13, 2005