AN1071 [ETC]
Information About the LM2650 Evaluation Board; 信息关于LM2650评估板
| 型号： | AN1071 |
| 厂家： | 
ETC |
| 描述： | Information About the LM2650 Evaluation Board |
| 文件： | 总6页 (文件大小：80K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
National Semiconductor
AN-1071
Steven Hunt
Information About the
LM2650 Evaluation Board
Rev. 1
September 1997
INTRODUCTION
For convenience, a sample of the LM2650 and eight other
components have been assembled: a 0.1 µF capacitor at
each of C1, C2, C6, and CB, a 0.2 µF capacitor at CVDD, a
0.01 µF capacitor at CSS, a 24.9 kΩ resistor at R2, and a 0Ω
resistor at R4. Of the eight, the first seven are common to
many applications, and the last is simply a jumper grounding
the SYNC input. When the synchronization feature is not be-
ing used, the SYNC input should be grounded.
A printed circuit board (PCB) has been developed. This ap-
plication note contains information about the board.
GENERAL DESCRIPTION
The LM2650 evaluation board is provided as a tool for devel-
oping DC/DC converters based on the LM2650 IC. It is con-
figured for single-output, step-down DC/DC converters. Fig-
ure 1 is a complete schematic of the board which can
accommodate up to 28 components including the LM2650.
Table 1 is a complete list of pads for placing components.
EXAMPLE CIRCUITS
The components contained in Tables 2, 3, and 4 can be used
to build typical application circuits. As with the design of any
DC/DC converter, the design of these involved tradeoffs be-
tween efficiency, size, and cost. The converters detailed in
Table 2 were designed with efficiency as the number one cri-
teria. Those detailed in Table 4 trade slightly higher switching
losses for a much smaller inductor.
Note: Not all applications will require the placement of all 28
components. The number of components placed depends
on the requirements of the application and the use of fea-
tures like programmable soft-start. The LM2650 evaluation
board is intended to be a reusable tool on which many differ-
ent converters meeting the requirements of many different
applications can be built. It is not intended to demonstrate
only one application of the LM2650.
AN100011-5
FIGURE 1. The LM2650 Evaluation Board Rev. 1 Schematic
THERMAL PERFORMANCE
2.0W respectively. These measurements were made in still
air. The junction-to-ambient thermal resistance of the pack-
aged IC alone in still air is 78˚C/W. The board is 0.063″ thick
FR-4 material.
The 24-lead SO package is a molded plastic package with a
solid copper lead frame. Most of the heat generated at the
die flows through the lead frame into the 3-ounce copper
planes on the board. The board then acts as a heat sink. The
junction-to-ambient thermal resistance of the packaged IC
mounted on the board has been measured to be 38˚C/W, 37
˚C/W, and 35 ˚C/W for the dissipation of 1.0W, 1.5W, and
ART
Figure 2 through Figure 4 show the PCB art work.
© 1997 National Semiconductor Corporation
AN100011
www.national.com
TABLE 1. A Complete List of Pads for Placing Components
# Notes
Label
U1
C1, C2, C3, and C4
C5
1
4
0
For placing the LM2650.
Capacitors placed here filter high-frequency switching noise from the input power rail.
These pads should not be labeled with a C. No component is placed here. They can be
used to ground the SLEEP LOGIC input. The pad connected to the SLEEP LOGIC pin can
be used to pull the input up.
C6
C9
1
1
A capacitor placed here also filters high-frequency switching noise from the input power rail
but at the VIN rail, the rail used by the signal-level circuits inside the IC.
Usually no component is placed here. A capacitor might be placed here for loop
compensation purposes, but most applications don’t use it.
C10
CB
1
1
1
A capacitor is placed here for loop compensation purposes.
The bootstrap capacitor is placed here.
CC
A capacitor is placed here for loop compensation purposes. This capacitor and an internal
6.5 kΩ resistor create an integrator pole.
CIN1 and CIN2
2
3
1
1
1
1
1
1
1
The bulk input capacitors are placed here.
COUT1, COUT2, and COUT3
The output filter capacitors are placed here.
A capacitor placed here programs the soft-start interval.
A capacitor placed here bypasses the output of the VDD regulator.
The inductor is placed here.
CSS
CVDD
L1
R1
One of the feedback resistors is placed here.
The other feedback resistor is placed here.
R2
R3
A resistor is placed here for loop compensation purposes.
R4
These pads can be used to ground the SYNC input when the synchronization feature is not
being used. The pad connected to the SYNC input can be used to connect the
synchronization signal. The evaluation board has a 0Ω jumper placed here to ground the
SYNC input.
RC
1
1
A resistor is also placed here for loop compensation purposes. This resistor and the
capacitor placed at CC create an integrator zero.
RFA
A resistor placed here adjusts the switching frequency up from the nominal 90 kHz. No
component is placed here for applications switching at 90 kHz.
RSIA and RSIC
2
2
Resistors placed here program the sleep-in threshold.
Resistors placed here program the sleep-out threshold.
RSOA and RSOC
TABLE 2. Components for Two Typical 90 kHz Application Circuits
Input Voltage
Applicable Cell Stacks
Output
7 to 18V IN
8- to 12-Cell NiCd or NiMH, 3- to 4-Cell Li Ion, 8- to 11-Cell Alkaline, 6-Cell Lead Acid
5V, 3A Out
3.3V, 3A Out
Input Filter Capacitors C1,
C2, and C6
0.1 µF ceramic chip capacitor
0.1 µF ceramic chip capacitor
Bootstrap Capacitor CB
Soft-start Capacitor CSS
0.1 µF ceramic chip capacitor
0.01 µF ceramic chip capacitor
0.2 µF ceramic chip capacitor
0.1 µF ceramic chip capacitor
0.01 µF ceramic chip capacitor
0.2 µF ceramic chip capacitor
VDD Bypass Capacitor
CVDD
Input Bulk Capacitors CIN1
and CIN2
22 µF, 35V AVX TPS Series or Sprague 593D
Series tantalum chip capacitor
22 µF, 35V AVX TPS Series or Sprague 593D
Series tantalum chip capacitor
Inductor L1
40 µH (See Table 3.)
33 µH (See Table 3.)
Output Capacitors COUT1,
COUT2, and COUT3
220 µF, 10V AVX TPS Series or Sprague
593D Series tantalum chip capacitor
220 µF, 10V AVX TPS Series or Sprague
593D Series tantalum chip capacitor
Feedback Resistors R1 and
R2
R1 = 75 kΩ, 1%, R2 = 24.9 kΩ, 1%
R1 = 41.2 kΩ, 1%, R2 = 24.9 kΩ, 1%
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2
TABLE 2. Components for Two Typical 90 kHz Application Circuits (Continued)
Compensation Components
RC, CC, R3, and C10
RC = 37.4 kΩ, CC = 4.7 nF, R3= 3.57
kΩ,C10 = 5.6 nF
RC = 23.2 kΩ, CC= 8.2 nF, R3 = 2.0 kΩ, C10
= 10 nF
Sleep Resistors RSIA and
RSOA
RSIA = 33 kΩ, RSOA = 200 kΩ
RSIA = 39 kΩ, RSOA = 130 kΩ
TABLE 3. Toroidal Inductors Using Cores from MICROMETALS, INC.
Core #
Core Material
Wire Gauge
AWG #23
AWG #23
AWG #21
AWG #21
# of Strands
# of Turns
15 µH
20 µH
33 µH
40 µH
T38
T38
−52
−52
−52
−18
1
1
1
1
21
25
41
41
T50
T50(B)
TABLE 4. Components for Two Typical 200 kHz Application Circuits
7 to 18V IN
Input Voltage
Applicable Cell Stacks
Output
8- to 12-Cell NiCd or NiMH, 3- to 4-Cell Li Ion, 8- to 11-Cell Alkaline, 6-Cell Lead Acid
5V, 3A Out
3.3V, 3A Out
Input Filter Capacitors C1, C2,
and C6
0.1 µF ceramic chip capacitor
0.1 µF ceramic chip capacitor
Bootstrap Capacitor CB
Soft-start Capacitor CSS
0.1 µF ceramic chip capacitor
0.01 µF ceramic chip capacitor
0.1 µF ceramic chip capacitor
0.01 µF ceramic chip
capacitor
VDD Bypass Capacitor CVDD
0.2 µF ceramic chip capacitor
0.2 µF ceramic chip capacitor
Input Bulk Capacitors CIN1
and CIN2
22 µF, 35V AVX TPS Series or Sprague 593D
Series tantalum chip capacitor
22 µF, 35V AVX TPS Series
or Sprague 593D Series
tantalum chip capacitor
Inductor L1
20 µH (See Table 3.)
15 µH (See Table 3.)
Output Capacitors COUT1,
COUT2, and COUT3
220 µF, 10V AVX TPS Series or Sprague
593D Series tantalum chip capacitor
220 µF, 10V AVX TPS Series
or Sprague 593D Series
tantalum chip capacitor
Feedback Resistors R1 and
R2
R1 = 75 kΩ, 1%, R2 = 24.9 kΩ, 1%
R1 = 41.2 kΩ, 1%, R2 = 24.9
kΩ, 1%
Compensation Components
RC, CC, R3, and C10
RC = 53.6 kΩ, CC = 2.7 nF, R3= 4.02 kΩ,
C10 = 4.7 nF
RC = 33.2 kΩ, CC= 3.9 nF,
R3 = 3.01 kΩ, C10 = 6.8 nF
Sleep Resistors RSIA and
RSOA
RSIA = 47 kΩ, RSOA = 200 kΩ
RSIA = 47 kΩ, RSOA = 91 kΩ
Frequency Adjusting Resistor
RFA
RFA = 24.9 kΩ
RFA = 24.9 kΩ
3
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AN100011-1
FIGURE 2. LM2650 Evaluation Board Top Silk Screen (Scale 1:1)
AN100011-2
FIGURE 3. LM2650 Evaluation Board Bottom Silk Screen (Scale 1:1)
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4
AN100011-3
FIGURE 4. LM2650 Evaluation Board Component Side (Scale 1:1)
AN100011-4
FIGURE 5. LM2650 Evaluation Board Solder Side (Scale 1:1)
5
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SEMICONDUCTOR CORPORATION. As used herein:
1. Life support devices or systems are devices or
systems which, (a) are intended for surgical implant
into the body, or (b) support or sustain life, and
whose failure to perform when properly used in
accordance with instructions for use provided in the
labeling, can be reasonably expected to result in a
significant injury to the user.
2. A critical component in any component of a life support
device or system whose failure to perform can be
reasonably expected to cause the failure of the life
support device or system, or to affect its safety or
effectiveness.
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