QPI-8 Datasheet, PDF (9/17 Pages) Vicor Corporation – AdvancedTCA™ Hot-Swap with Active EMI Filter

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QPI-8
QUIETPOWER^
QPI-8 Timing Waveforms
The waveforms in Figure 17 are the typical start-up
waveforms that would be seen in a system where two current
pulses are required to completely charge the bulk
capacitance to the bus voltage. The GATE waveform is an
internal signal and cannot be measured externally; it is shown
only for reference.
Once VIN is established and the UV and OV thresholds are
satisfied, the internal FET’s gate will start to get driven high
after a 15ms delay. This delay allows for insertion de-
bouncing. As the FET turns “on” and allows the passing of
current the magnitude of the current is monitored. Once it
reaches the 6A circuit breaker threshold an internal fault
timer is started and the current is limited to a 12A maximum
value. If the current does not drop to a value below the 6A
circuit breaker limit before the fault timer ends then the gate
is shut “off” and remains off for about 95ms. After this time
the gate is again turned on and current is allowed to pass.
Once the current is below the circuit breaker limit, the FET is
fully turned “on” to its minimum r_ds value and the Powergood
pin is released (open drain).
The change in voltage across VSW is dependent upon the
value of the bulk capacitance that the QPI-8 is charging. The
circuit breaker fault time is 300us when the voltage on VSW is
greater than 40V, referenced to BUS-; or if there is no voltage
change across VSW during the 12A current pulse, indicating a
short across the bulk capacitor. Once below the 40V limit,
and a decreasing voltage across VSW, the fault time is
increased to 1.2ms to charge the bulk capacitors faster.
The timing waveforms for an OV (Over-voltage) and UV
(Under-voltage) events are shown in Figure 18. After the
initial start-up delay, the internal FET’s gate is turned on.
Once its gate-to-source voltage reaches 8V it releases the
PWRGD pin and allows it to get pulled up to VIN.
In the event of an OV fault, the QPI-8 will turn off its internal
FET and it will remain off until the OV fault is cleared. Once
cleared, the gate immediately starts to turn back on. With an
UV fault, the FET is again turned off, but the gate is not
turned back on until 15ms after the UV fault has been
cleared.
Figure 17 - QPI-8 current fault timing diagram.
Picor Corporation · picorpower.com
QPI-8
Rev 1.5, Page 9 of 17