PI3101 Datasheet, PDF (7/18 Pages) Vicor Corporation – 36-75V Input, 3.3V / 18A / 60W Output Very High Density Isolated DC-DC Converter (400W/in3)

Functional Description:
Input Power Pins IN(+) and IN(-):
The input power pins on the PI3101 are connected
to the input power source which can range from 36V
to 75V DC. Under surge conditions, the PI3101 can
withstand up to 100V DC for 100ms without incurring
damage. The user should take care to avoid driving
the input rails above the specified ratings. Since the
PI3101 is designed with high reliability in mind, the
input pins are continuously monitored. If the applied
voltage exceeds the input over-voltage trip point
(typically 80V) the conversion process shall be
terminated immediately. The converter initiates soft-
start automatically within 80ms after the input
voltage is reduced back to the appropriate value.
The input pins do not have reverse polarity
protection. If the PI3101 is operated in an
environment where reverse polarity is a concern, the
user should consider using a polarity protection
device such as a suitably rated diode. To avoid the
high losses of using a diode, the user should
consider the much higher efficiency Picor family of
intelligent Cool-ORing^TM solutions that can be used
in reverse polarity applications. Information is
available at picorpower.com.
The PI3101 will draw nearly zero current until the
input voltage reaches the internal start up threshold.
If the ENABLE pin is not pulled low by external
circuitry, the output voltage will begin rising to its
final value of 3.3V about 80ms after the input UV
lockout releases. This will occur automatically even if
the ENABLE pin is floating.
To help keep the source impedance low, the input to
the PI3101 should be bypassed with (2) 1uF 100V
ceramic capacitors of X7R dielectric in parallel with a
low Q 47uF 100V electrolytic capacitor. To reduce
EMI and reflected ripple current, a series inductor of
2 to 4.7uH can be added. The input traces to the
module should be low impedance configured in such
a manner as to keep stray inductance minimized.
ENABLE Pin:
The ENABLE pin serves as a multi-function pin for
the PI3101. During normal operation, it outputs the
on-board 4.9V regulator which can be used for
trimming the module up. The ENABLE pin can also
be used as a remote enable pin either from the
secondary via an optocoupler and some external
isolated bias supply or from the primary side through
a small signal transistor, FET or any device that
sinks 3.3mA, minimum. If the ENABLE pin is lower
than 2.35V typical, the converter will be held off or
shut down if already operating. A third feature is
offered in that during a fault condition such as output
OVP, input UV or OV, or output current limit, the
ENABLE pin is pulled low internally. This can be
used as a signal to the user that a fault has
occurred. Whenever the ENABLE pin is pulled low,
the TRIM/SS pin follows, resetting the internal and
external soft-start circuitry. All faults will pull
ENABLE low including over temperature. If
increased turn on delay is desired, the ENABLE pin
can be bypassed with a small capacitor up to a
maximum of 1500pF.
TRIM/SS Pin:
The TRIM/SS pin serves as another multi-purpose
pin. First, it is used as the reference for the internal
error amplifier. Connecting a resistor from TRIM/SS
to SGND allows the reference to be margined down
by as much as 10%. Connecting a resistor from
TRIM/SS to ENABLE will allow the reference and
output voltage to be margined up by 10%. If the user
wishes a longer start up time, a small ceramic
capacitor can be added to TRIM/SS to increase it. It
is critical to connect any device between TRIM/SS
and SGND and not -IN, otherwise high frequency
noise will be introduced to the reference and
possibly cause erratic operation.
TM Pin:
The TM pin serves as an output indicator of the
internal package temperature which is within
approximately +/- 5 K of the hottest junction
temperature. Because of this, it is a good indicator of
a thermal overload condition. The output is a scaled,
buffered analog voltage which indicates the internal
temperature in degrees Kelvin. Upon a thermal
overload, the TM pin is pulled low, indicating a
thermal fault has occurred. Upon restart of the
converter, the TM pin reverts back to a buffered
monitor. The thermal shutdown function of the
PI3101 is a fault feature which interrupts power
processing if a certain maximum temperature is
exceeded. TM can be monitored by an external
microcontroller or circuit configured as an adaptive
fan speed controller so that air flow in the system
can be conveniently regulated.
SGND Pin:
The PI3101 SGND pin is the “quiet” control circuitry
return. It is basically an extension of the internal
signal ground. To avoid contamination and potential
ground loops, this ground should NOT be connected
to -IN since it is already star connected inside the
package. Connect signal logic to SGND, not -IN.
Picor Corporation • picorpower.com
PI3101-00-HVIZ Rev 1.1, April 29^th, 2010 Page 7 of 18