Evaluation Board Hardware Description
KIT33908MBEVBE Evaluation Board User’s Guide
, Rev. 1.0 3/2014
Freescale Semiconductor, Inc.
9
10.1
The Analog Section
10.1.1 Overview
Figure 5. Power Management Section
10.1.2 V
CORE
Output Capacitance (JP126)
Output capacitance has an impact on the feedback (FB_core), which is necessary for controlling the V
CORE
voltage through a compensation network. For test purposes on the EVM, two different capacities are selectable
due to the jumper JP126 (if the jumper is disconnected, output capacitance is set to 20 µF, otherwise to 40 µF),
see
Jumper Definitions
. These capacities simulate capacity of the real circuitry normally connected to V
CORE
.
Changing the output capacitance has an impact on a selection of the compensation network.
10.1.3 Compensation Network (JP115 &JP117)
The voltage regulator needs feedback from the V
CORE
voltage to be able to adjust (control) output voltage. For
this reason, a compenstation network is implemented in the external MC33908 circuitry. Static feedback
(steady-state) voltage is defined by a simple resistor bridge (given by R119/R121 and R133). Dynamic behavior
of the regulator is controlled by an RC network (defined by R124, R126, C127, C130, R135, R136, C128, C129).
Compensation network is shown on the
Figure 6
. Steady-state voltage can be chosen (either 1.23 or 3.3 V). To
tune the dynamic performance, the board is equipped with two different networks (possible combinations of the
jumpers JP115 and JP117 are shown in the
Table 1
). The combinations shown in
Table 1
were chosen for an
optimal performance for the given output voltage. The real dynamic performance can differ for different
applications, and can be tuned by changing the compensation network, and by adding output capacitors
(JP126).
