
STARTUP INHIBIT PERIOD
The Startup Inhibit Period ensures that the converter will
remain off for at least 200ms when it is shut down for any
reason. When an output short is present, this generates a
5Hz "hiccup mode," which prevents the converter from over-
heating. In all, there are seven ways that the converter can
be shut down, initiating a Startup Inhibit Period:
Input Under-Voltage Lockout
Input Over-Voltage Shutdown (not present in Quarter-
brick)
Output Over-Voltage Protection
Over Temperature Shutdown
Current Limit
Short Circuit Protection
Turned off by the ON/OFF input
Figure F shows three turn-on scenarios, where a Startup
Inhibit Period is initiated at t0, t1, and t2:
Before time t0, when the input voltage is below 34V (typ.),
the unit is disabled by the Input Under-Voltage Lockout fea-
ture. When the input voltage rises above 34V, the Input
Under-Voltage Lockout is released, and a Startup Inhibit
Period is initiated. At the end of this delay, the ON/OFF pin
is evaluated, and since it is active, the unit turns on.
At time t1, the unit is disabled by the ON/OFF pin, and it
cannot be enabled again until the Startup Inhibit Period has
elapsed.
When the ON/OFF pin goes high after t2, the Startup Inhibit
Period has elapsed, and the output turns on within the 4ms
(typ.) "Turn On Time."
Product # PQ48050QNA20
Phone 1-888-567-9596
Doc.# 005-2QN450D_B
9/5/01
Page 12
Technical Specification
48Vin 5.0Vout 20A
Quarter
Brick
Under-Voltage
Lockout Turn-On
Threshold
ON/OFF
(pos logic)
Figure F: Startup Inhibit Period (turn-on time not to scale)
Vout
Vin
200ms
(typical start-up
inhibit period)
t
0
t
1
t
2
t
4ms (typical
turn on time)
ON
OFF