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參數(shù)資料
| 型號(hào)： | LM2647LQX |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | Dual Synchronous Buck Regulator Controller |
| 中文描述： | DUAL SWITCHING CONTROLLER, 345 kHz SWITCHING FREQ-MAX, QCC28 |
| 封裝： | LLP-28 |
| 文件頁數(shù)： | 21/25頁 |
| 文件大?。?/td> | 763K |
| 代理商： | LM2647LQX |
Application Information
(Continued)
TABLE 1. Losses and Efficiency
Upper
54
611
665
Lower
98
30
128
Pcond (mW)
Psw (mW)
PFET (mW)
P
IC
(mW)
Pind (mW)
Ptotal (mW)
Pout (=VoxIo) (mW)
28
257
1078
15000
93%
Vo=5V, Io=3A,Vin=20V, f=300kHz, DCR=26m
, Si4828DY.
Typical efficiency curves for different input voltages are avail-
able under Typical Performance Characteristics.
LAYOUT GUIDELINES
For a deeper understanding of Buck converters and the
‘critical traces’please seeApplication NoteAN-1229 at http://
power.national.com.
Figure 14
is based on such an understanding of the critical
sections and also the pin functions of the LM2647. Refer to
the Typical Applications circuit and the LM2647 TSSOP pi-
nouts to understand the layout suggestions more thoroughly.
The components shown in
Figure 14
are most critical and
must be placed close to the device and connected onto a
ground island on the component side. Several vias can then
connect to the ground plane at the locations indicated. The
FETs are positioned close to the controller and are also very
close to each other to minimize inductances.
After the critical components are placed, the resistor to the
frequency adjust pin (R19) must also be placed close to the
IC connecting to SGND. This will reduce noise pickup and
jitter.
The feedback trace can also pick up noise and it must be
routed away from sources of noise/EMI, particularly the
FETs and inductors.
Enough copper area must be left around the FETs for ther-
mal dissipation. More details on this are also provided in
AN-1229.
Note that the current limit detector circuit compares the
voltage on the ILIM pin with respect to the PGND pin.
Therefore, if the power ground is noisy it can lead to errone-
ous triggering of the current limit detector. This will manifest
itself as an inability to meet the load requirement despite
oversizing the current limit resistor. It can also lead to failure
of the output to recover after encountering an overload con-
dition. Therefore, it is strongly recommended that a solid
ground plane be created as the first internal plane right
below the component side.Several vias should be gener-
ously placed to connect the ground nodes of the component
layer to this ground plane.
SETTING OUTPUT VOLTAGE
From the TypicalApplication circuit on Page 1, it can be seen
that R15 and R16 are used to set V
O2
whereas R21 and R22
set V
O1
. For either channel, calling the upper resistor (con-
nected to one end of the droop resistor) R
U
and the lower
resistor (connected to ground) R
L
the following equation is
applicable.
Therefore from the Bill of Material:
For
channel #1
(V
O1
= 5V
),
R
U
= R21 = 43.2k
R
L
= R22 = 5.9k
For
channel #1
(V
O2
= 3.3V
),
R
U
= R15 = 43.2k
R
L
= R16 = 9.53k
So
This is as per the requirement of the primary end-application.
Other output voltage values are possible by adjusting the
resistor ratios (but note that there are maximum duty cycle
constraints as stated in Electrical Characteristics table)
which will limit the range of output voltages achievable. Note
that the upper resistor is involved in fixing the gain of the
error amplifier, and therefore its value has been set to an
‘optimum’ value of 43.2k for both channels. This value helps
in achieving good step response and ensuring stability.
Therefore, in general, only the lower resistor should be
adjusted. However the more experienced designer can judi-
ciously use the open-loop gain information provided in the
next section, to change both upper and lower resistor values
if required.
20056343
FIGURE 14. Critical Component placement (TSSOP)
L
www.national.com
21
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM2647LQX/NOPB | 功能描述:DC/DC 開關(guān)控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風(fēng)格: 封裝 / 箱體:CPAK |
| LM2647MTC | 功能描述:DC/DC 開關(guān)控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風(fēng)格: 封裝 / 箱體:CPAK |
| LM2647MTC/NOPB | 功能描述:DC/DC 開關(guān)控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風(fēng)格: 封裝 / 箱體:CPAK |
| LM2647MTCX | 功能描述:DC/DC 開關(guān)控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風(fēng)格: 封裝 / 箱體:CPAK |
| LM2647MTCX/NOPB | 功能描述:DC/DC 開關(guān)控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風(fēng)格: 封裝 / 箱體:CPAK |
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