QPI-8L Datasheet, PDF (4/8 Pages) Vicor Corporation – AdvencedTCA Hot-Swap Sip With Active EMI Filter

PRELIMINARY
90.00
80.00
70.00
60.00
50.00
40.00
30.00
0
OV-HI
OV-LO
5000
UV-HI
UV-LO
10000 15000 20000
Series Resistor
25000
30000
Figure 6 – Trimming UV/OV with external series resistor.
Figure 8 – 5ms BUS transient, 42 W load
CH1: VBUS, CH3: PWRGD, CH4: Converter load current
UVENLO = ^{2.5 (RUVEN + 108450)}
8450
UVENHI = 2.5 V + (RUVEN + 100 K) (316 µA)
OVLO = 2.5 V + (ROV + 200 K) (348 µA)
OVHI = ^{2.5 (ROV + 206800)}
6800
Figure 7 – UVEN and OV resistor equations.
To prevent the QPI-8 from going into a fault mode and
deasserting the Powergood signal after the transient, the
converter’s input capacitors must be sized so that they can
be completely restored in the time of one 12 A current
pulse, about 1 ms, and still maintain the required input
current of the converter. If greater bulk capacitance is
required for higher loads, then the circuit in Figure 9c
could be used to slowly charge the capacitors. To reduce
bulk capacitance and take advantage of the V² energy
relationship, a boost circuit with a switch-over function
can be used to charge fewer bulk storage capacitors to a
higher voltage.
It is critical to keep the load current on the converter’s
input capacitor to less than 25 mA during the initial
power-up phase. This limit is set by the current limit level
and the duty cycle of the circuit breaker timer.
Once Powergood has been asserted the full load can
be enabled.
An external capacitor CE, shown in Figures 9a and 9b, will
provide the required UVEN hold-up filtering during the
ATCA's 5 ms, zero-volt BUS transient requirement. Figure 8
shows the effects of CE during a BUS transient event.
Using a 2.2 µF CE capacitor and 1 mF of converter input
capacitance will enable this circuit to support a 42 W load
for the 5 ms transient. The Powergood state of the QPI-8
remains unchanged during this transient, allowing the
converter to maintain its output power to the load.
Picor Corporation • www.picorpower.com
QPI-8L Data Sheet Rev. 1.0 Page 4 of 8