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LM5642EVAL-KIT/NOPB 产品设计参考手册 - TI（德州仪器）
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TEXAS INSTRUMENTS LM5642EVAL-KIT/NOPB 评估电路板, LM5642 降压转换器
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LM5642EVAL-KIT/NOPB数据手册
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User's Guide
SNVA070B–May 2004–Revised April 2013
AN-1292 LM5642 Evaluation Board
1 Introduction
The LM5642 IC is a dual channel, current-mode, synchronous buck converter controller. It can handle
input voltages of up to 36V and delivers two independent output voltages from 1.23V up to 90% of the
input voltage. Current sensing can be done using a dedicated resistor or using the R
DS(ON)
of the high-side
FET. This application note describes the dedicated evaluation PCBs that are available for both methods.
2 Resistor Sense PCB
The first, more common method of sensing current in current-mode controllers is with an external sense
resistor, placed in series with the high-side FET of each channel. Sense resistors provide an accurate
voltage as the load current passes through them, and have stable, linear resistance change with
temperature. As shipped the Resistor Sense PCB is designed to deliver 1.8V on Channel 1 at a maximum
current of 7A, and 3.3V on Channel 2 at a maximum current of 4A. The input voltage can vary anywhere
from 5.5 to 36V. The board has been designed to be flexible and allow many other circuit configurations
by replacing the original components with user selected ones. Figure 1 shows the circuit diagram
representing the standard BOM that comes with the PCB. Table 1 lists all the components that are used
for this standard configuration BOM. Figure 2 shows the complete circuit diagram with all extra footprints.
Two SPST switches, S1 and S2, are provided to turn the two channels of the converter on and off. The
standard BOM that comes with the LM5642 Resistor Sense evaluation board uses 10mΩ current sense
resistors (R7 for Channel 1 and R15 for Channel 2) to provide independent feedback signals to the IC.
The board provides additional resistor and capacitor footprints for noise filtering, ringing control, and to
enable operation at low input voltages.
3 Current Sense Filters
R-C filters have been added to the current sense amplifier inputs of the Resistor Sense evaluation board,
comprised of components C3, C4, C14, C15, R2, R6, and R16. These resistors and capacitors reduce the
sensitivity to switching noise, especially during high currents, load-transients, and circuits with short on-
times.
4 Parallel Operation
The two channels of the LM5642 Resistor Sense evaluation board can be paralleled to provide one high
current rail. At the nominal switching frequency of 200kHz the converter will run 180° out-of-phase. Care
must be taken when using this feature combined with the frequency synchronization, as the two channels
of the converter are no longer 180° out-of-phase when the frequency is above or below 200kHz. The two
feedback inputs FB1 and FB2 should be tied together by soldering a 0Ω resistor in the position marked J1
on the bottom side of the PCB. The two COMP pins should be tied together by soldering a 0Ω resistor in
the position J3. The ON/SS1 and ON/SS2 pins must also be connected using a 0Ω resistor in the position
J2. One of the two SPDT switches S1 and S2 should be left ‘ON’ and the other used to turn the converter
off and on. Finally, the two outputs VO1 and VO2 must be tied together by the user, external to the PCB.
Only one of the two resistor divider networks (R10/R11 or R19/R20) and only one of the compensation
networks should be used (C18/C19/R22/R23 or C20/C21R24/R25).
All trademarks are the property of their respective owners.
1
SNVA070B–May 2004–Revised April 2013 AN-1292 LM5642 Evaluation Board
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