Tyco TX 75149 - Manual (Page 9)

9
Click to Calculate Stability
model of the capacitor bank. The load is modeled by the resistance R
L
.
The second configuration is similar to the first one except that the voltage sense
location is moved from the output pins of the module to the load. In this case,
the voltage sensed and regulated is not the module output voltage but the
voltage across the load, a situation commonly referred to as "remote sensing".
The remaining three configurations (3, 4 and 5) allow the inclusion of more
detailed models of the capacitor banks and parasitic elements between the
module and the load. In some applications, the power module is mounted on a
separate printed circuit board and supplies a number of loads on different
PCBs. In this case, it is common to have one capacitor bank on the power
board and another one on the load board.
The first capacitor bank, which is a parallel combination of three capacitors, is
usually located as close as possible to the module output pins. It conveniently allows
for modeling different types of capacitors such as aluminum and tantalum
electrolytics and ceramics. When the size and type of capacitors used in a bank are
different, their individual frequency responses vary greatly from one another and
hence they cannot be modeled as a lumped capacitor as shown in the first two
configurations. Note that if you only have one or two types of capacitors, you can still
use the model by setting the values corresponding to the other capacitor to zero.
The second capacitor bank is typically placed as close as possible across the
load terminals to improve dynamic response during load transients by minimizing the
voltage overshoot and undershoot. The capability of modeling two capacitors with
their ESR and ESL are provided to model different types and sizes of capacitors.
The three configurations also allow for modeling various sense points for the
feedback voltage. Feedback voltage can be sensed across the load (case 3), across
the capacitor bank (case 2), or across the module output.
Click on the configuration picture suitable for your application. In this example, we
will choose Configuration 4. Clicking on the picture will bring that configuration's
page as shown in Figure 4.
The top left section shows the configuration circuit with the feedback voltage
sense path depicted in red. Underneath the configuration circuit diagram, circuit
parameters are listed with default values that can be edited in blue. The
JFW050A module is a 5V, 10A output module and hence in this example, the
load resistance is set at 0.5 ohms, indicating a 10A load. You should set the load
resistance value corresponding to the actual load in your application. The
resistors R
a1
, through R
a3
, and R
b1
through R
b3
are the ESRs of the capacitors
and the inductances L
a1
through L
b3
are the ESLs.
Enter all circuit parameters of your application. When you finish editing the
parameter values, click on the
button.