Texas Instruments TPS54373EVM-237, Руководство пользователя, Страница: 13 / 36

Modifications
1-5 Introduction
Figure 1–1. Frequency Trimming Resistor Selection Graph
250
300
350
400
450
500
550
600
650
700
750
60 70 80 90 100 110 120 130 140 150 160 170 180
Switching Frequency – kHz
Resistance – k
Ω
The TPS54373EVM–237 EVM supports alternate output filter configurations
by means of pads located on the back side of the PCB. The positions for C15
and C16 provide space for one or two electrolytic type surface-mount
capacitors as an alternative to the ceramic types provided. Since changes in
the output filter affects the overall loop response, the user may find it desirable
to change the values used in the compensation network (R1, R3, R5, C6, C7
and C8) the 0-
Ω
resistor R7 in the feedback path is provided as a convenient
place to break the loop for testing any compensation value changes. While the
provided compensation network can provide a stable output for a wide variety
of output filter component values, it is always a good idea to verify any changes
to the output filter or compensation network.
The primary intended usage for the TPS54373 device family is in applications
requiring a precharge condition on the output. These types of applications
include power supplies for DSPs and microprocessors where the I/O and core
voltages must track each other within a certain amount during start-up. The
TPS54373 incorporates disable sink during start-up to allow this type of
functionality in the SWIFT family of dc/dc converters. A typical design
approach is to tie the output of the core voltage to the output of the I/O voltage
with a number of series diodes so that the core voltage is at a level equal to
the I/O voltage minus the drop across the diodes during start-up. The
TPS54373EVM-237 EVM provides four series diodes, D1 through D4, and
allows the user to precharge the output from either the EVM input voltage or
an external source. To use the input voltage as the precharge source, install
a jumper across the J3 header. To supply an external source, use the J4
connector terminals, while leaving J3 open. Headers J5 and J6 are provided
to select two, three or four series diodes. Install a jumper across the header
to bypass the adjacent diode. Care must be taken to use the correct number
of diodes for the application.