Tyco Electronics Corp.. 13
Data Sheet
July 2002 dc-dc Converters; 36 to 75 Vdc Input, 3.3 Vdc Output; 165 W to 198 W
FW250F1 and FW300F1 Power Modules:
Feature Descriptions (continued)
Synchronization
Any module can be synchronized to any other module
or to an external clock using the SYNC IN or SYNC
OUT pins. The modules are not designed to operate in
a master/slave configuration; that is, if one module fails,
the other modules will continue to operate.
SYNC IN Pin
This pin can be connected either to an external clock or
directly to the SYNC OUT pin of another FW250x or
FW300x module.
If an external clock signal is applied to the SYNC IN
pin, the signal must be a 500 kHz (±50 kHz) square
wave with a 4 Vp-p amplitude. Operation outside this
frequency band will detrimentally affect the perfor-
mance of the module and must be avoided.
If the SYNC IN pin is connected to the SYNC OUT pin
of another module, the connection should be as direct
as possible, and the V
I(–) pins of the modules must be
shorted together.
Unused SYNC IN pins should be tied to V
I(–). If the
SYNC IN pin is unused, the module will operate from
its own internal clock.
SYNC OUT Pin
This pin contains a clock signal referenced to the V
I(–)
pin. The frequency of this signal will equal either the
module’s internal clock frequency or the frequency estab-
lished by an external clock applied to the SYNC IN pin.
When synchronizing several modules together, the
modules can be connected in a daisy-chain fashion
where the SYNC OUT pin of one module is connected
to the SYNC IN pin of another module. Each module in
the chain will synchronize to the frequency of the first
module in the chain.
To avoid loading effects, ensure that the SYNC OUT
pin of any one module is connected to the SYNC IN pin
of only one module. Any number of modules can be
synchronized in this daisy-chain fashion.
Overtemperature Shutdown
To provide protection in a fault condition, the unit is
equipped with an overtemperature shutdown circuit.
The shutdown circuit will not engage unless the unit is
operated above the maximum case temperature.
Recovery from overtemperature shutdown is
accomplished by cycling the dc input power off for at
least 1.0 s or toggling the primary referenced on/off
signal for at least 1.0 s.
Forced Load Sharing (Parallel Operation)
For either redundant operation or additional power
requirements, the power modules can be configured for
parallel operation with forced load sharing (see
Figure 23). For a typical redundant configuration,
Schottky diodes or an equivalent should be used to
protect against short-circuit conditions. Because of the
remote sense, the forward-voltage drops across the
Schottky diodes do not affect the set point of the
voltage applied to the load. For additional power
requirements, where multiple units are used to develop
combined power in excess of the rated maximum, the
Schottky diodes are not needed.
Good layout techniques should be observed for noise
immunity. To implement forced load sharing, the follow-
ing connections must be made:
■ The parallel pins of all units must be connected
together. The paths of these connections should be
as direct as possible.
■ All remote-sense pins should be connected to the
power bus at the same point, i.e., connect all
SENSE(+) pins to the (+) side of the power bus at the
same point and all SENSE(–) pins to the (–) side of
the power bus at the same point. Close proximity and
directness are necessary for good noise immunity.
