HPQ-12-D48_11 Datasheet, PDF (13/14 Pages) Murata Manufacturing Co., Ltd. – Isolated 300-Watt Quarter Brick DC/DC Converters

HPQ-12/25-D48 Series
Isolated 300-Watt Quarter Brick DC/DC Converters
HPQ Restart Delay (See Specification Note 10)
When the HPQ undergoes shutdown through loss or cycling of the input power,
a 555 timer enable block circuit is triggered to provide a restart delay to assure
systematic restart of the converter. The delay time is a function both of the
recovery time of the input voltage and the 555 reset time.
Thus, there are two distinct scenarios for the restart delay, which are detailed
below.
Scenario I: Vin recovers quickly.
When the input voltage recovers quickly, the VCC for the 555 timer remains
active to lockout the output for the programmed delay time. The delay time in
this scenario is then equal to the 555 hiccup recovery time. This is internally
set to a nominal value of 3s. This is illustrated in the scope shot below:
Vin (20V per division), Vout (5V per division) at 500ms (1/2 S per division).
Scenario II: Vin recovers after more than 2.5s (restart delay time less than
15ms)
When the input voltage is absent greater than 2.5s, the energy for the Vcc to
the 555 timer enable block will be exhausted. Since this is a sufficient period
to guarantee systematic restart of the converter, the output will start after just
a 15ms delay from the application of input power. This scenario is illustrated in
the scope shot below.
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21 Feb 2011 MDC_HPQ-12/25-D48 Series.A07 Page 13 of 14