Module – GE Industrial Solutions 12V Mega TLynx User Manual

Page 14

Data Sheet
May 4, 2012

12V Mega TLynx

: Non-Isolated DC-DC Power Modules:

6.0 – 14Vdc Input; 0.8Vdc to 3.63Vdc Output; 30A output

current

LINEAGE

POWER

Good layout techniques should be observed when
using multiple units in parallel. To implement forced
load sharing, the following connections should be
made:

• The share pins of all units in parallel must be

connected together. The path 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 the SENSE

(+)

pins to the

(+)

side of the bus.

Close proximity and directness are necessary
for good noise immunity

Some special considerations apply for design of
converters in parallel operation:
• When sizing the number of modules required

for parallel operation, take note of the fact that
current sharing has some tolerance. In
addition, under transient condtions such as a
dynamic load change and during startup, all
converter output currents will not be equal. To
allow for such variation and avoid the likelihood
of a converter shutting off due to a current
overload, the total capacity of the paralleled
system should be no more than 75% of the
sum of the individual converters. As an
example, for a system of four 12V Mega
TLynx

converters in parallel, the total current

drawn should be less that 75% of (4 x 30A) ,
i.e. less than 90A.

• All modules should be turned on and off

together. This is so that all modules come up at
the same time avoiding the problem of one
converter sourcing current into the other
leading to an overcurrent trip condition. To
ensure that all modules come up
simultaneously, the on/off pins of all paralleled
converters should be tied together and the
converters enabled and disabled using the
on/off pin.

• The share bus is not designed for redundant

operation and the system will be non-functional
upon failure of one of the unit when multiple
units are in parallel. In particular, if one of the
converters shuts down during operation, the
other converters may also shut down due to
their outputs hitting current limit. In such a
situation, unless a coordinated restart is
ensured, the system may never properly restart
since different converters will try to restart at
different times causing an overload condition
and subsequent shutdown. This situation can
be avoided by having an external output
voltage monitor circuit that detects a shutdown
condition and forces all converters to shut
down and restart together.

When not using the active load sharing feature,
share pins should be left unconnected.

Tunable Loop

The 12V Mega TLynx

modules have a new

feature that optimizes transient response of the
module called Tunable Loop

External capacitors are usually added to the output
of the module for two reasons: to reduce output
ripple and noise (see Fig. 29) and to reduce output
voltage deviations from the steady-state value in the
presence of dynamic load current changes. Adding
external capacitance however affects the voltage
control loop of the module, typically causing the
loop to slow down with sluggish response. Larger
values of external capacitance could also cause the
module to become unstable.

The Tunable Loop

allows the user to externally

adjust the voltage control loop to match the filter
network connected to the output of the module. The
Tunable Loop

is implemented by connecting a

series R-C between the SENSE and TRIM pins of
the module, as shown in Fig. 34. This R-C allows
the user to externally adjust the voltage loop
feedback compensation of the module.

MODULE

VOUT

SENSE

TRIM

GND

RTUNE

CTUNE

RTrim

C O

Figure. 34. Circuit diagram showing connection
of R

TUME

and C

TUNE

to tune the control loop of

the module.

Recommended values of R

TUNE

and C

TUNE

for

different output capacitor combinations are given in
Tables 2 and 3. Table 2 shows the recommended
values of R

TUNE

and C

TUNE

for different values of

ceramic output capacitors up to 1000uF that might
be needed for an application to meet output ripple
and noise requirements. Selecting R

TUNE

and C

TUNE

according to Table 2 will ensure stable operation of
the module.

In applications with tight output voltage limits in the
presence of dynamic current loading, additional