NIS5112 ON Semiconductor, NIS5112 Datasheet - Page 7

• Manufacturer Part Number: NIS5112
• Description: Electronic Fuse
• Manufacturer: ON Semiconductor

Basic Operation
It contains circuits to monitor the input voltage, output
current, die temperature, turn-on di/dt and turn-on dV/dt, as
well as an enable/timer function.
the input voltage to the load based on the restrictions of the
controlling circuits. The dV/dt of the output voltage can be
programmed by the addition of a capacitor to the dV/dt pin,
or if left open, the output current will be limited by the
internally controlled di/dt.
not exceed the 135°C limit that is programmed into the chip.
The current limit circuit does not shut down the part but will
reduce the conductivity of the FET to maintain a constant
current as long as it remains at the set level. The input
overvoltage clamp also does not shut down the part, but will
limit the output voltage to 15 V in the event that the input
exceeds that level.
function, which can also be used to reset the device after a
thermal fault if the thermal latch version is chosen.
of the internal N-channel power FET and also for the current
limit circuit. The remainder of the control circuitry operates
between the input voltage (V
dV/dt
current source as shown in Figure 9. The enable circuit
controls a FET that keeps the slew-rate capacitor discharged
any time the device is disabled. When the enable pin is
released (low-to-high transition) or when power is applied
with the enable pin in a high state, the dV/dt capacitor begins
to charge due to the 80 mA in the current source. The
amplifier controls the output voltage and tracks the voltage
on the dV/dt cap scaled by a factor of 2. The output voltage
will continue to ramp higher until it reaches the input
voltage, or until the 15 V clamp limits it.
The equation for the output slew rate is
dV/dt = (I/C
Where:
I – is 80 mA (internal current source)
C
This step causes a current surge into the output load
capacitance which can be seen in Figure 6. The peak level
of this surge will be limited to the overload level of the
current limit.
dV/dt
This device is a self-protected, resettable, electronic fuse.
On application of the input voltage, the device will apply
The device will remain on as long as the temperature does
The device can be turned on and off by the enable/timer
An internal charge pump provides bias for the gate voltage
This circuit is comprised of an operational amplifier and
The dV/dt ramp begins with a small step of about 200 mV.
– is the desired dV/dt capacitor value.
dV/dt
) x 2.
CC
) and ground.
DEVICE OPERATION
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NIS5112
7
Overvoltage Clamp
reference. It monitors the output voltage and if the output
voltage exceeds 15 V, the gate drive of the main FET is
reduced to limit the output. This is intended to allow
operation through transients while protecting the load. If an
overvoltage condition exists for many seconds, the device
may overheat due to the voltage drop across the FET
combined with the load current. In this event, the thermal
protection circuit would shut down the device.
Enable/Timer
pin, or as a time delay. In the enable mode, an open collector
device is connected to this pin. When the device is in its low
impedance mode, this pin is low and the operation of the chip
is disabled. If a time delay is required, a capacitor is added
to this pin.
the turn on will be delayed from the time at which the UVLO
voltage is reached. If an open collector device is also used,
the delay will start from the time that it goes into its high
impedance state. The capacitor is charged by an internal
current source of 80 mA (typical).
was designed to be compatible with most logic families. In
general, logic gates can be tied directly to this pin, but it is
recommended that this be tested.
The overvoltage clamp consists of an amplifier and
The enable/timer pin can function either as a direct enable
If a capacitor is added without an open collector device,
The nominal trip voltage of the comparator is 2.5 V and
dV/dt
80 mA
+
-
Figure 9. dV/dt Circuit
Enable
R
R
Source