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QPI-9 Data Sheet Rev. 1.3 Page 6 of 8

Start-up

The following oscilloscope pictures show the hot swap

BUS- current, QPI- to Bus- voltage and PWRGD to BUS-

output voltage of the QPI-9 during operation. Figures

10 and 11 are the QPI-9's in-rush characteristics under

two load capacitance conditions. In Figure 10 a 470 µF

capacitor required roughly 330 ms to completely

charge from a 24 V bus voltage. The QPI-9 can drive

large amounts of bulk capacitance to maintain

converter operation during a 0V bus transient event, as

shown in Figure 11 with a 4700 µF load capacitance.

Under this condition the PWRGD takes about 2.9

seconds to go high after the UVEN input is pulled high

upon the complete insertion of the board into the

shelf. Figure 11's time-scale is too long to show the

current pulses that charge the bulk capacitance.

After insertion, when the UVEN voltage exceeds 18 V

the UV detection fault is cleared, the QPI-9 goes

through a delay cycle (~45 ms) to allow for system

stabilization and de-bounce. After this time, the QPI- to

BUS- path is turned on and current is allowed to pass,

monitored by the current sense function. Initially the

current level exceeds the 6 A circuit breaker limit, the

event timer starts and the power good state is not

valid. The sense function and linear control loop will

allow twice the circuit breaker current to pass. If the

current does not drop below the circuit breaker level

prior to reaching the timer limit, typically 800 µS, the

QPI- to BUS- path will open. The effective duty cycle

under the current limit condition is approximately 1%.

Once the load capacitors are fully charged to the input

bus potential, the load condition falls below 6 A and

the PWRGD pin is asserted high, providing that the bus

supply is still within the UV and OV range.

Transient Protection and Recovery

Figures 12 and 13 show the QPI-9's ability to handle

low resistance shorts (< 2) at the load terminals to

emulate fast and slow blown fuse events. In Figure 12,

the transient short is 2 seconds long and the QPI- to

BUS- path is opened within 1 ms of this occurrence.

Figure 13 demonstrates the QPI-9's performance with a

short circuit on its output, where it remains in a low

duty cycle mode until the short is removed, then

restarts normally.

Figure 10 – 470 µF capacitor @ 24 V.

Figure 12 – 2 seconds short-circuit.

Figure 13 – Start-up into short circuit.

Figure 11 – 4700 µF capacitor @ 24 V.