GE Industrial Solutions 40A Digital MegaDLynx - Manual (Page 15)

GE
Data Sheet
40A Digital MegaDLynx TM : Non-Isolated DC-DC Power Modules
4.5Vdc –14.4Vdc input; 0.45Vdc to 2.0Vdc output; 40A Output Current
April 24, 2013 ©2012 General Electric Company. All rights reserved. Page 15
Tunable Loop TM
The module has a feature that optimizes transient response
of the module called Tunable Loop
TM .
External capacitors are usually added to the output of the
module for two reasons: to reduce output ripple and noise
(see Figure 38) 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 TM 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
TM is implemented
by connecting a series R-C between the VS+ and TRIM pins of
the module, as shown in Fig. 28. This R-C allows the user to
externally adjust the voltage loop feedback compensation of
the module.
Figure. 28. Circuit diagram showing connection of R
TUNE
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 Table 2. 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 output capacitance
will be required. Table 3 lists recommended values of R
TUNE
and C
TUNE
in order to meet 2% output voltage deviation limits
for some common output voltages in the presence of a 20A
to 40A step change (50% of full load), with an input voltage of
12V.
Please contact your GE technical representative to obtain
more details of this feature as well as for guidelines on how
to select the right value of external R-C to tune the module
for best transient performance and stable operation for other
output capacitance values.
Table 2. General recommended values of of R
TUNE
and
C
TUNE
for Vin=12V and various external ceramic capacitor
combination
C
O
6x
47µF
8x
47µF
10x
47µF
12x
47µF
20x
47µF
R
TUNE
330Ω 330Ω 330Ω 330Ω 200Ω
C
TUNE
330pF 820pF 1200pF 1500pF 3300pF
Table 3. Recommended values of R
TUNE
and C
TUNE
to obtain
transient deviation of 2% of Vout for a 20A step load with
Vin=12V.
V
O
1.8V 1.2V 0.6V
C
O
4x47uF +
6x330µF
polymer
4x47uF +
11x330µF
polymer
4x47uF +
12x680µF
polymer
R
TUNE
220 Ω 200 Ω 180 Ω
C
TUNE
5600pF 12nF 47nF
∆V 34mV 22mV 12mV
Note: The capacitors used in the Tunable Loop tables are
47 μF/3 mΩ ESR ceramic, 330 μF/12 mΩ ESR polymer
capacitor and 680μF/12 mΩ polymer capacitor.
VS+
MODULE
SIG_GND
TR IM
VOUT
RTune
CTune
RTrim
CO
GN D