PI31XX-01-HVIZ Datasheet, PDF (15/18 Pages) Vicor Corporation – 24VIN, 5V and 12VOUT, ZVS Isolated Converter Module Family

Functional Description
DC-DC
Converter
MADE
IN
USA
U.S. PATS. LISTED ON PACKING MATERIALS & DATASHEETS
Figure 21 — Picor PI31xx-01-HVIZ Shown With System Fuse,
Filter, Decoupling And Extended Soft Start
Input Power Pins IN(+) and IN(-)
The input power pins on the PI31xx-01-HVIZ are connected to
the input power source which can range from 18V to 36V_DC.
Under surge conditions, the PI31xx-01-HVIZ can withstand up
to 45V_DC for 100ms without incurring damage. The user should
take care to avoid driving the input rails above the specified
ratings. Since the PI31xx-01-HVIZ is designed with high reliability
in mind, the input pins are continuously monitored. If the applied
voltage exceeds the input over-voltage trip point, 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 PI31xx-01-HVIZ 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^® solutions that can be used in
reverse polarity applications. Information is available
at vicorpower.com.
The PI31xx-01-HVIZ 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 output value 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
PI31xx-01-HVIZ should be bypassed with (2) 4.7µF 50V ceramic
capacitors of X7R dielectric in parallel with a low Q 100µF 50V
electrolytic capacitor. To reduce EMI and reflected ripple current,
a series inductor of 0.2 to 0.47µH 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
The ENABLE pin serves as a multi-function pin for the
PI31xx-01-HVIZ. 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
24 Volt
Page 15 of 18
Rev 1.4
02/2015
PI31xx-01-HVIZ
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 -20%. 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.
Referring to the figures below, the appropriate trim up or trim
down resistor can be calculated using the equivalent circuit
diagram and the equations. When trimming up the trim down
resistor is not populated and when trimming down, the trim up
resistor is not populated. The soft start time is adjustable within
the limits defined by the data tables and has a default value of
500µs to reach steady state. The internal soft start capacitor
value is 10nF.
ENABLE
PI31xx
VERO
10k
RSS
TRIM/SS
Vref
•
SGND
Rhigh
•
Rlow
•
( ) _{( )} ^R_low ⁼
–V_desired
•
R_INT
–Vout_nom + V_desired
( ) ⁽ _[( ⁾ _{) + ]} R_high =
–RSS
•
–Vout_nom • V_ERO + V_desired • V_ref
V_ref –Vout_nom V_desired
Figure 22 — Trim Equations And Equivalent Circuit
C_REF =
T_ssdesired – 230 • 10^−6
23000
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