Diodes NIS5132 User Manual
Page 8
NIS5132
Document number: DS36457 Rev. 1 - 5
8 of 11
December 2013
© Diodes Incorporated
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NIS5132
Application Note
Theory of Operation
The NIS5132 is a self protected, resettable electronic fuse. It monitors the input and output voltage, the output current and the die temperature.
When the NIS5132 is powered up it will ramp up the output voltage based on the dv/dt setting (see description below) and current will begin to
flow. The device current limit can be set with an external resistor, the ramp rate (dv/dt) can be adjusted with an external capacitor. The
Overvoltage Clamp, Under Voltage Lockout and Thermal Protection are internally set.
Current Limit
The NIS5132 incorporates a sensefet with a reference and amplifier to control the current in the device. The sensefet uses a small fraction of
the load current to measure the actual current. This reduces the losses as a smaller sense resistor can be used. The current can be measured
direct with the R
s
resistor connected between the load and the I
SENSE
pin. (see Figure 1). That method includes the resistance of the bond
wires in the current limiting circuit. Or a Kelvin connection (see Figure 2) can be used, in that case one of the 5 source pins will be used and
the voltage is measured on the die eliminating the bond wire resistance. That reduces the source pins to the load to four and with that
increases the on resistance of the effuse to the load.
Overvoltage Clamp
The NIS5132MN1 and NIS5132MN2 monitor the input voltage and clamp it once it exceeds 15V. This will allow for transient on the input for
short periods of time. If the input voltage stays above 15V for extended times the voltage drop across the FET with the load current will
increase the die temperature and the thermal shutdown feature will protect the device and shut it down.
Under Voltage Lock Out
The input voltage of NIS5132 is monitored by an UVLO circuit (under voltage lockout) if the input voltage drops below this threshold the output
transistor will be pulled into a high impedance state.
dv/dt
The NIS5132 has an integrated control circuit Enable/Fault
The NIS5132 has a tri state Enable/Fault pin. It is used to turn on and off the device with high and low signals from a GPIO, but can also
indicate a thermal fault. When the Enable/Fault pin is pulled low the output is turned off, when the Enable/Fault pin is pulled high the output is
turned on. In the event of a thermal fault the Enable/Fault pin will be pulled low to an intermediate voltage by an internal circuit. This can be
used to chain up to 4 NIS5132 (or NIS5135) together that during a thermal shut down the linked devices turn off as well.
Due to this fault indication capability it should not be connected to any type of logic with an internal pull up device.
NIS5132MN1 connected to a 2
nd
device or connected to NIS5135MN1 will latch off until the Enable/Fault pin has been pulled to low and then
allowed to go back up to a high signal, or if the power has been cycled. Once the part starts up again it will go through the start up ramp
determined by the internal circuit or based on the externally connected capacitor on pin dv/dt.
The MN2 devices will auto restart once the part that indicated a thermal shutdown has cooled down. It will also go through the start up ramp.
Figure 18 Enable/Fault Signal Levels
Thermal Protection
The NIS5132 has an integrated temperature sensing circuit that protects the die in the event of over temperature. The trip point has been
intentionally set high at 175˚C to allow for increase trip times during high power transient events. The NIS5132 will shut down current flow to
the output when the die temperature reaches 175°C. The NIS5132MN1 will restart after the Enable pin has been toggled or the input power
has been cycled. The NIS5132MN2 will auto restart after the die temperature has been reduced by ~45°C.
Even that the thermal trip point has been set high to allow for high current transients the circuit design should accomplish best thermal
performance with good thermal layout of the PCB. It is not recommended to operate NIS5132 above 150°C over extended periods of time.