LM3678SD-1.2/NOPB [TI]
用于便携式应用的高性能、微型 1.5A 降压直流/直流转换器 | DSC | 10 | -30 to 85;
| 型号： | LM3678SD-1.2/NOPB |
| 厂家： | 
TEXAS INSTRUMENTS |
| 描述： | 用于便携式应用的高性能、微型 1.5A 降压直流/直流转换器 | DSC | 10 | -30 to 85 便携式 开关 光电二极管 转换器 |
| 文件： | 总19页 (文件大小：1978K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LM3678
www.ti.com
SNVS464C –APRIL 2008–REVISED MAY 2013
High-Performance Miniature 1.5-A Step-Down DC-DC Converter for Handheld Applications
Check for Samples: LM3678
1
FEATURES
DESCRIPTION
The LM3678 step-down DC-DC converter is
optimized for powering low-voltage circuits from a
single Li-Ion cell battery and input voltage rails from
2.5 V to 5.5 V. It provides up to 1.5-A load current,
over the entire input voltage range. LM3678 offers a
0.8V or 1.2V option. One of the pair of voltages is set
through the VSELECT pin.
2
•
VOUT = 0.8 V or 1.2 V
•
•
•
VIN = 2.5 V to 5.5 V
1.5-A Maximum Load Capability
3.3-MHz (Typical) PWM Fixed Switching
Frequency Allows Use of 1-µH Inductor
•
•
•
±3% DC Output Voltage Precision
0.01-µA (Typical) Shutdown Current
LM3678 operates in PWM mode with
a fixed
frequency of 3.3 MHz. Internal synchronous
rectification provides high efficiency during PWM
mode operation. In shutdown mode, the device turns
off and reduces battery consumption to 0.01 µA
(typical).
Internal Synchronous Rectification for High
Efficiency
•
•
Internal Soft Start
Current Overload and Thermal Shutdown
Protection
The LM3678 is available in a 3mm x 3mm DSC-10
package. A high switching frequency of 3.3 MHz
(typical) allows use of tiny surface-mount
components. Only three external surface-mount
components, an inductor and two ceramic capacitors,
are required (solution size less than 33 mm2). For
voltages other than the voltage shown, contact TI or
your distributor.
APPLICATIONS
•
•
•
•
•
•
PDAs and Smart Phones
Personal Media Players
W-LAN
USB Modem Applications
Digital Still Cameras
Portable Hard Disk Drives
Efficiency vs. Output Current
( VOUT = 1.2V)
Typical Application Circuit
1 mH
V
= 2.5V to 5.5V
IN
V
VDD
VDD
OUT
SW
FB
CIN
10 mF
22 mF
C
OUT
90
80
70
60
50
40
30
20
10
0
0.8V/1.2V
VSELECT
EN
LM3678
PWM
PGOOD
GND
GND
NOTE: VSEL H = 1.2V, VSEL L = 0.8V
0.100
0.010
1.000
LOAD (A)
10.000
Figure 1.
Figure 2.
1
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
All trademarks are the property of their respective owners.
2
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2008–2013, Texas Instruments Incorporated
LM3678
SNVS464C –APRIL 2008–REVISED MAY 2013
www.ti.com
Functional Block Diagram
V
EN
SW
IN
Current Limit
Comparator
+
Undervoltage
Lockout
Ramp
Generator
Soft
Start
-
Ref1
PFM Current
Comparator
Thermal
Bandgap
+
2 MHz
Oscillator
Shutdown
-
Ref2
PWM Comparator
+
-
Error
Amp
Control Logic
Driver
V
REF
+
-
0.5V
+
-
V
COMP
1.0V
+
-
Zero Crossing
Comparator
Frequency
Compensation
Fixed Ver
FB
GND
VSELECT
PGOOD PWM
Figure 3. LM3678 Block Diagram
2
Submit Documentation Feedback
Copyright © 2008–2013, Texas Instruments Incorporated
Product Folder Links: LM3678
LM3678
www.ti.com
SNVS464C –APRIL 2008–REVISED MAY 2013
Connection Diagram and Package Mark Information
GND
1
FB
EN
10
9
FB
GND
GND
1
2
10
9
2
GND
EN
D
A
P
D
A
P
8
PWM
PWM
PGOOD
8
7
3
4
SW
3
SW
VDD
VDD
4
5
PGOOD
VSELECT
7
VDD
6
6
5
VDD
VSELECT
Figure 4. Top View
Figure 5. Bottom View
Table 1. Pin Descriptions
Pin
No.
Name
Description
1
2
3
4
5
6
GND
GND
Power Ground pin.
Analog Ground Pin
SW
Switching node connection to the internal PFET switch and NFET synchronous rectifier
Analog supply input. Connect to the input filter capacitor (see Figure 1).
Power supply Input. Connect to the input filter capacitor (see Figure 1).
VDD
VDD
VSELECT
Output voltage select (For example)
VSELECT = LOW, VOUT = 0.8V
VSELECT = HIGH , VOUT = 1.2V
7
PGOOD
Power Good Flag. This common drain logic output is pulled to ground when the output voltage is not within
±7.5% of regulation.
8
9
PWM
EN
Connect PWM pin to VIN.
Enable pin. The device is in shutdown mode when voltage to this pin is <0.4V and enabled when >1.0V. Do not
leave this pin floating.
10
FB
Feedback analog input. Connect directly to the output filter capacitor for fixed voltage versions.
DAP
DAP
Die Attach Pad, connect the DAP to GND on PCB layout to enhance thermal performance. It should not be used
as a primary ground connection.
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
Absolute Maximum Ratings(1)
VIN Pin: Voltage to GND
EN Pin
−0.2V to 6.0V
−0.2V to 6.0V
FB, SW Pin
Continuous Power Dissipation(2)
(GND−0.2V) to (VIN + 0.2V)
Internally Limited
+150°C
Junction Temperature (TJ-MAX
Storage Temperature Range
)
−65°C to +150°C
260°C
Maximum Lead Temperature (Soldering, 10 seconds)
(1) Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings are conditions under
which the device operates. Operating Ratings do not imply specified performance limits. For specified performance limits and associated
test conditions, see the Electrical Characteristics.
(2) Internal thermal shutdown circuitry protects the device from permanent damage. Thermal shutdown engages at TJ= 150°C (typ) and
disengages at TJ= 130°C (typ).
Copyright © 2008–2013, Texas Instruments Incorporated
Submit Documentation Feedback
3
Product Folder Links: LM3678
LM3678
SNVS464C –APRIL 2008–REVISED MAY 2013
www.ti.com
Operating Ratings(1)(2)
Input Voltage Range
2.5V to 5.5V
0mA to 1.5A
Recommended Load Current
Junction Temperature (TJ) Range
Ambient Temperature (TA) Range(3)
−30°C to +125°C
−30°C to +85°C
(1) Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings are conditions under
which the device operates. Operating Ratings do not imply specified performance limits. For specified performance limits and associated
test conditions, see the Electrical Characteristics.
(2) All voltages are with respect to the potential at the GND pin.
(3) In applications with high power dissipation or poor package resistance, the maximum ambient temperature may need to be derated.
Maximum ambient temperature (TA-MAX) is dependent on the maximum operating junction temperature (TJ-MAX), the maximum power
dissipation of the device in the application (PD-MAX) and the junction to ambient thermal resistance of the package (θJA) in the
application, as given by the following equation: TA-MAX= TJ-MAX− (θJAx PD-MAX).
Thermal Properties
Junction-to-Ambient Thermal Resistance (θJA) (DSC-10) for 4-layer board
(1)
49.8°C/W
(1) Junction-to-ambient thermal resistance is highly application and board layout dependent. In applications where high power dissipation
exists, special care must be given to thermal dissipation issues in board design.
Electrical Characteristics(1)(2)(3)(4)
Limits in standard typeface are for TJ = 25°C. Limits in boldface type apply over the full operating ambient temperature range
(−30°C ≤ TA ≤ +85°C). Unless otherwise noted, specifications apply to the LM3678 Typical Application Circuit (see Figure 1)
with VIN = EN = 3.6V
Symbol
VFB
Parameter
Feedback voltage
Test Conditions
Min
-3
Typ
Max
+3
Unit
%
VSELECT = Low and High
VREF
RDSON (P)
RDSON (N)
ILIM
Internal reference voltage
0.5
150
110
2.15
V
Pin-to-pin resistance for PFET
Pin-to-pin resistance for NFET
Switch peak current limit
VIN= VGS= 3.6V
VIN= VGS= 3.6V
Open loop
200
150
2.4
1
mΩ
mΩ
A
1.9
1.2
ISHDN
VIH
Shutdown supply current
EN = 0V
µA
V
Logic high input for EN and VSELECT
Logic low input for EN and VSELECT
Enable (EN) input current
VIN = 3.6V
VIL
VIN = 3.6V
0.4
1
V
IEN
0.01
3.3
µA
MHz
FOSC
Internal oscillator frequency
PWM Mode
2.7
3.6
(1) All voltages are with respect to the potential at the GND pin.
(2) Refer to Typical Performance Characteristics for closed loop data and its variation with regards to supply voltage and temperature.
Electrical Characteristics reflects open loop data (FB=0V and current drawn from SW pin ramped up until cycle by cycle current limit is
activated). Closed loop current limit is the peak inductor current measured in the application circuit by increasing output current until
output voltage drops by 10%.
(3) The parameters in the electrical characteristic table are tested at VIN= 3.6V unless otherwise specified. For performance over the input
voltage range, see Typical Performance Characteristics.
(4) Min and Max limits are specified by design, test or statistical analysis. Typical numbers represent the most likely norm.
4
Submit Documentation Feedback
Copyright © 2008–2013, Texas Instruments Incorporated
Product Folder Links: LM3678
LM3678
www.ti.com
SNVS464C –APRIL 2008–REVISED MAY 2013
Typical Performance Characteristics
LM3678SD, Circuit of Figure 1, VIN= 3.6V, VOUT= 1.2V, CIN = 10µF, COUT = 22µF, and TA= 25°C, unless otherwise noted.
Quiescent Supply Current vs. Temperature
Switching Frequency vs. Temperature
500
3.50
3.45
3.40
3.35
3.30
3.25
3.20
3.15
3.10
3.05
3.00
475
450
425
400
375
350
325
300
275
250
-30
-10
10
30
50
70
90
-30
-10
10
30
50
70
90
TEMPERATURE (°C)
TEMPERATURE (°C)
Figure 6.
Figure 7.
NFET_ RDSON vs. Temperature
PFET_RDSON vs. Temperature
220
200
180
160
140
120
100
80
150
140
130
120
110
100
90
80
70
10
-30
-10
10
30
50
70
90
-30
-10
30
50
70
90
TEMPERATURE (°C)
TEMPERATURE (°C)
Figure 8.
Figure 9.
ILIMIT vs. Temperature (Open Loop)
Efficiency PWM Mode vs. ILOAD (0.8V)
90
80
70
60
50
40
30
20
10
0
2.50
2.45
2.40
2.35
2.30
2.25
2.20
2.15
2.10
2.05
2.00
1.95
1.90
-30
-10
10
30
50
70
90
0.0001 0.0010 0.010 0.100 1.000 10.000
TEMPERATURE (°C)
LOAD (A)
Figure 10.
Figure 11.
Copyright © 2008–2013, Texas Instruments Incorporated
Submit Documentation Feedback
5
Product Folder Links: LM3678
LM3678
SNVS464C –APRIL 2008–REVISED MAY 2013
www.ti.com
Typical Performance Characteristics (continued)
LM3678SD, Circuit of Figure 1, VIN= 3.6V, VOUT= 1.2V, CIN = 10µF, COUT = 22µF, and TA= 25°C, unless otherwise noted.
Line Transient Response
(VOUT = 0.8V, LOAD = 500mA)
Efficiency PWM Mode vs. ILOAD (1.2V)
90
80
70
60
50
40
30
20
10
0
.0001 0.0010 0.010 0.100 1.000 10.000
LOAD (A)
Figure 12.
Figure 13.
Line Transient Response
(VOUT = 1.2V, LOAD = 500mA)
Load Transient Response
(VIN = 3.6V, VOUT = 1.2V, Load Step 0 ↔ 500mA)
Figure 14.
Figure 15.
Load Transient Response
(VIN = 3.6V, VOUT = 0.8V, Load Step 0 ↔ 500mA)
Load Transient Response
(VIN = 3.6V, VOUT = 0.8V, Load Step 500mA ↔ 1A)
Figure 16.
Figure 17.
6
Submit Documentation Feedback
Copyright © 2008–2013, Texas Instruments Incorporated
Product Folder Links: LM3678
LM3678
www.ti.com
SNVS464C –APRIL 2008–REVISED MAY 2013
Typical Performance Characteristics (continued)
LM3678SD, Circuit of Figure 1, VIN= 3.6V, VOUT= 1.2V, CIN = 10µF, COUT = 22µF, and TA= 25°C, unless otherwise noted.
Load Transient Response
(VIN = 3.6V, VOUT = 1.2V, Load Step 500mA ↔ 1A)
VSELECT Transient Response
(VIN = 3.6V, LOAD = 500mA)
Figure 18.
Figure 19.
VSELECT Transient Response
(VIN = 3.6V, No LOAD)
VSELECT Transient Response
(VIN = 3.6V, LOAD = 1A)
Figure 20.
Figure 21.
Start Up
Start Up
(VIN = 3.6V, VOUT = 1.2V, LOAD = 1A)
(VIN = 3.6V, VOUT = 1.2V, LOAD = 500mA)
Figure 22.
Figure 23.
Copyright © 2008–2013, Texas Instruments Incorporated
Submit Documentation Feedback
7
Product Folder Links: LM3678
LM3678
SNVS464C –APRIL 2008–REVISED MAY 2013
www.ti.com
Typical Performance Characteristics (continued)
LM3678SD, Circuit of Figure 1, VIN= 3.6V, VOUT= 1.2V, CIN = 10µF, COUT = 22µF, and TA= 25°C, unless otherwise noted.
Switching Waveform
(VOUT = 1.2V, LOAD = 1A)
Figure 24.
8
Submit Documentation Feedback
Copyright © 2008–2013, Texas Instruments Incorporated
Product Folder Links: LM3678
LM3678
www.ti.com
SNVS464C –APRIL 2008–REVISED MAY 2013
OPERATION DESCRIPTION
DEVICE INFORMATION
The LM3678, a high-efficiency step-down DC-DC switching buck converter, delivers a constant voltage from a
single Li-Ion battery and input voltage rails from 2.5 V to 5.5 V to portable devices such as cell phones and
PDAs. Using a voltage mode architecture with synchronous rectification, the LM3678 has the ability to deliver up
to 1.5 A, depending on the input voltage, output voltage, ambient temperature and the inductor chosen.
Additional features include soft start, undervoltage protection, current overload protection, and thermal shutdown
protection. As shown in Figure 1, only three external power components are required for implementation.
The part uses an internal reference voltage of 0.5 V. It is recommended to keep the part in shutdown until the
input voltage is 2.5 V or higher.
CIRCUIT OPERATION
During the first portion of each switching cycle, the control block in the LM3678 turns on the internal PFET
switch. This allows current to flow from the input through the inductor to the output filter capacitor and load. The
inductor limits the current to a ramp with a slope of (VIN–VOUT)/L, by storing energy in a magnetic field.
During the second portion of each cycle, the controller turns the PFET switch off, blocking current flow from the
input, and then turns the NFET synchronous rectifier on. The inductor draws current from ground through the
NFET to the output filter capacitor and load, which ramps the inductor current down with a slope of - VOUT/L.
The output filter stores charge when the inductor current is high, and releases it when inductor current is low,
smoothing the voltage across the load.
The output voltage is regulated by modulating the PFET switch on time to control the average current sent to the
load. The effect is identical to sending a duty-cycle modulated rectangular wave formed by the switch and
synchronous rectifier at the SW pin to a low-pass filter formed by the inductor and output filter capacitor. The
output voltage is equal to the average voltage at the SW pin.
PWM OPERATION
During device operation the converter operates as a voltage-mode controller with input voltage feed forward. This
allows the converter to achieve good load and line regulation. The DC gain of the power stage is proportional to
the input voltage. To eliminate this dependence, feed forward inversely proportional to the input voltage is
introduced.
The output voltage is regulated by switching at a constant frequency and then modulating the energy per cycle to
control power to the load. At the beginning of each clock cycle the PFET switch is turned on and the inductor
current ramps up until the comparator trips and the control logic turns off the switch. The current limit comparator
can also turn off the switch in case the current limit of the PFET is exceeded. Then the NFET switch is turned on
and the inductor current ramps down. The next cycle is initiated by the clock turning off the NFET and turning on
the PFET.
Figure 25. Typical PWM Operation
Copyright © 2008–2013, Texas Instruments Incorporated
Submit Documentation Feedback
9
Product Folder Links: LM3678
LM3678
SNVS464C –APRIL 2008–REVISED MAY 2013
www.ti.com
INTERNAL SYNCHRONOUS RECTIFICATION
The LM3678 uses an internal NFET as a synchronous rectifier to reduce rectifier forward voltage drop and
associated power loss. Synchronous rectification provides a significant improvement in efficiency whenever the
output voltage is relatively low compared to the voltage drop across an ordinary rectifier diode.
CURRENT LIMITING
A current limit feature allows the LM3678 to protect itself and external components during overload conditions by
implementing current limiting with an internal comparator that trips at 2.15A (typ). If the output is shorted to
ground the device enters a timed current limit mode where the NFET is turned on for a longer duration until the
inductor current falls below a low threshold. This allows the inductor current more time to decay, thereby
preventing runaway.
SHUTDOWN MODE
Setting the EN input pin low (<0.4V) places the LM3678 in shutdown mode. During shutdown the PFET switch,
NFET switch, reference, control and bias circuitry of the LM3678 are turned off. Setting EN high (>1.0V) enables
normal operation. It is recommended to set EN pin low to turn off the LM3678 during system power up and
undervoltage conditions when the supply is less than 2.5V. Do not leave the EN pin floating.
SOFT START
The LM3678 has a soft-start circuit that limits in-rush current during start-up. During start-up the switch current
limit is increased in steps. Soft start is activated only if EN goes from logic low to logic high after VIN reaches
2.5V. Soft start is implemented by increasing switch current limit in steps of 250mA, 500mA, 1A and 2A (typical
switch current limit). The start-up time thereby depends on the output capacitor and load current demanded at
start-up.
Inductor Selection
There are two main considerations when choosing an inductor; the inductor should not saturate, and the inductor
current ripple should be small enough to achieve the desired output voltage ripple. Different saturation current
rating specifications are followed by different manufacturers so attention must be given to details. Saturation
current ratings are typically specified at 25°C. However, ratings at the maximum ambient temperature of
application should be requested from the manufacturer. Shielded inductors radiate less noise and should be
preferred.
There are two methods to choose the inductor saturation current rating.
Method 1:
The saturation current should be greater than the sum of the maximum load current and the worst case average
to peak inductor current. This can be written as
>
ISAT IOUTMAX + IRIPPLE
VIN - VOUT
VOUT
VIN
1
≈
∆
«
’* ≈
÷ ∆
◊ «
’* ≈ ’
where IRIPPLE
=
÷ ∆ ÷
2 * L
◊ « f ◊
(1)
•
•
•
•
•
•
IRIPPLE: average to peak inductor current
IOUTMAX: maximum load current (1.5A)
VIN: maximum input voltage in application
L : minimum inductor value including worst case tolerances (30% drop can be considered for method 1)
f : minimum switching frequency (2.7Mhz)
VOUT: output voltage
For a more conservative approach, a 1µH inductor with a saturation current rating of at least 2.5A is
recommended for most applications.
10
Submit Documentation Feedback
Copyright © 2008–2013, Texas Instruments Incorporated
Product Folder Links: LM3678
LM3678
www.ti.com
SNVS464C –APRIL 2008–REVISED MAY 2013
Input Capacitor Selection
A ceramic input capacitor of 10uF, 6.3V is sufficient for most applications. Place the input capacitor as close as
possible to the VIN pin of the device. A larger value may be used for improved input voltage filtering. Use X7R or
X5R types; do not use Y5V. DC bias characteristics of ceramic capacitors must be considered when selecting
case sizes like 0805 and 0603. The input filter capacitor supplies current to the PFET switch of the LM3678 in
the first half of each cycle and reduces voltage ripple imposed on the input power source. A ceramic capacitor’s
low ESR provides the best noise filtering of the input voltage spikes due to this rapidly changing current. Select a
capacitor with sufficient ripple current rating. The input current ripple can be calculated as:
2
VOUT
VIN
VOUT
VIN
r
≈
∆
«
’
÷
◊
1 -
+
*
IRMS = IOUTMAX
*
12
(VIN - VOUT) V
*
OUT
r =
L f I
* *
V
IN
*
OUTMAX
*
The worst case is when VIN = 2 VOUT
(2)
Table 2. Suggest Inductors and Their Suppliers
Model
Vendor
Dimensions
LxWxH (mm)
D.C.R (max)
ISAT
NR4012T1R0N
LPS4012-102L
LPS4012-102L
Taiyo Yuden
Coilcraft
4 x 4 x 1.2
60mΩ
100mΩ
40mΩ
2.5A
2.5A
3.4A
3.9 x 3.9 x 1.2
3.9 x 3.9 x 1.8
Coilcraft
Output Capacitor Selection
A ceramic output capacitor of 22µF, 6.3V is sufficient for most applications. Use X7R or X5R types; do not use
Y5V. DC bias characteristics of ceramic capacitors must be considered when selecting case sizes like 0805 and
0603. DC bias characteristics vary from manufacturer to manufacturer and dc bias curves should be requested
from them as part of the capacitor selection process.
The output filter capacitor smooths out current flow from the inductor to the load, helps maintain a steady output
voltage during transient load changes and reduces output voltage ripple. These capacitors must be selected with
sufficient capacitance and sufficiently low ESR to perform these functions.
The output voltage ripple is caused by the charging and discharging of the output capacitor and by the RESR and
can be calculated as:
Voltage peak-to-peak ripple due to capacitance can be expressed as follow:
IRIPPLE
=
VPP-C
4*f*C
(3)
Voltage peak-to-peak ripple due to ESR can be expressed as follow:
VPP-ESR = (2 * IRIPPLE) * RESR
Because these two components are out of phase the RMS (root mean squared) value can be used to get an
approximate value of peak-to-peak ripple.
The peak-to-peak ripple voltage RMS value can be expressed as follow:
2
VPP-RMS
=
VPP-C2 + VPP-ESR
(4)
Note that the output voltage ripple is dependent on the inductor current ripple and the equivalent series
resistance of the output capacitor (RESR).
The RESR is frequency dependent (as well as temperature dependent); make sure the value used for calculations
is at the switching frequency of the part.
Copyright © 2008–2013, Texas Instruments Incorporated
Submit Documentation Feedback
11
Product Folder Links: LM3678
LM3678
SNVS464C –APRIL 2008–REVISED MAY 2013
www.ti.com
Table 3. Suggested Capacitors and Their Suppliers
Case Size
Inch (mm)
Model
10µF for CIN
Type
Vendor
Voltage Rating
GRM21BR60J106K
JMK212BJ106K
Ceramic, X5R
Ceramic, X5R
Ceramic, X5R
Murata
Taiyo-Yuden
TDK
6.3V
6.3V
6.3V
0805 (2012)
0805 (2012)
0805 (2012)
C2012X5R0J106K
22µF for COUT
JMK212BJ226MG
Ceramic, X5R
Taiyo-Yuden
6.3V
0805 (2012)
Board Layout Considerations
PC board layout is an important part of DC-DC converter design. Poor board layout can disrupt the performance
of a DC-DC converter and surrounding circuitry by contributing to EMI, ground bounce, and resistive voltage loss
in the traces. These can send erroneous signals to the DC-DC converter IC, resulting in poor regulation or
instability.
Good layout for the LM3678 can be implemented by following a few simple design rules below.
1. Place the LM3678, inductor and filter capacitors close together and make the traces short. The traces
between these components carry relatively high switching currents and act as antennas. Following this rule
reduces radiated noise. Special care must be given to place the input filter capacitor very close to the VIN
and GND pin.
2. Arrange the components so that the switching current loops curl in the same direction. During the first half of
each cycle, current flows from the input filter capacitor through the LM3678 and inductor to the output filter
capacitor and back through ground, forming a current loop. In the second half of each cycle, current is pulled
up from ground through the LM3678 by the inductor to the output filter capacitor and then back through
ground forming a second current loop. Routing these loops so the current curls in the same direction
prevents magnetic field reversal between the two half-cycles and reduces radiated noise.
3. Connect the ground pins of the LM3678 and filter capacitors together using generous component-side
copper fill as a pseudo-ground plane. Then, connect this to the ground-plane (if one is used) with several
vias. This reduces ground-plane noise by preventing the switching currents from circulating through the
ground plane. It also reduces ground bounce at the LM3678 by giving it a low-impedance ground connection.
4. Use wide traces between the power components and for power connections to the DC-DC converter circuit.
This reduces voltage errors caused by resistive losses across the traces.
5. Route noise sensitive traces, such as the voltage feedback path, away from noisy traces between the power
components. The voltage feedback trace must remain close to the LM3678 circuit and should be direct but
should be routed opposite to noisy components. This reduces EMI radiated onto the DC-DC converter’s own
voltage feedback trace. A good approach is to route the feedback trace on another layer and to have a
ground plane between the top layer and layer on which the feedback trace is routed. In the same manner for
the adjustable part it is desired to have the feedback dividers on the bottom layer.
6. Place noise sensitive circuitry, such as radio IF blocks, away from the DC-DC converter, CMOS digital blocks
and other noisy circuitry. Interference with noise-sensitive circuitry in the system can be reduced through
distance.
For detailed layout information, refer to Application Note 1722 LM3678 Evaluation Board SNVA289.
In mobile phones, for example, a common practice is to place the DC-DC converter on one corner of the board,
arrange the CMOS digital circuitry around it (since this also generates noise), and then place sensitive
preamplifiers and IF stages on the diagonally opposing corner. Often, the sensitive circuitry is shielded with a
metal pan and power to it is post-regulated to reduce conducted noise, using low-dropout linear regulators.
12
Submit Documentation Feedback
Copyright © 2008–2013, Texas Instruments Incorporated
Product Folder Links: LM3678
LM3678
www.ti.com
SNVS464C –APRIL 2008–REVISED MAY 2013
REVISION HISTORY
Changes from Revision B (April 2013) to Revision C
Page
•
Changed layout of National Data Sheet to TI format .......................................................................................................... 12
Copyright © 2008–2013, Texas Instruments Incorporated
Submit Documentation Feedback
13
Product Folder Links: LM3678
PACKAGE OPTION ADDENDUM
www.ti.com
10-Dec-2020
PACKAGING INFORMATION
Orderable Device
Status Package Type Package Pins Package
Eco Plan
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
Samples
Drawing
Qty
(1)
(2)
(3)
(4/5)
(6)
LM3678SD-1.2/NOPB
LM3678SDE-1.2/NOPB
ACTIVE
ACTIVE
WSON
WSON
DSC
DSC
10
10
1000 RoHS & Green
250 RoHS & Green
SN
Level-1-260C-UNLIM
Level-1-260C-UNLIM
-30 to 85
-30 to 85
S021B
S021B
SN
(1) The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2) RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of <=1000ppm threshold. Antimony trioxide based
flame retardants must also meet the <=1000ppm threshold requirement.
(3) MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
(4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.
(5) Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation
of the previous line and the two combined represent the entire Device Marking for that device.
(6)
Lead finish/Ball material - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead finish/Ball material values may wrap to two
lines if the finish value exceeds the maximum column width.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and
continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
Addendum-Page 1
PACKAGE OPTION ADDENDUM
www.ti.com
10-Dec-2020
Addendum-Page 2
PACKAGE MATERIALS INFORMATION
www.ti.com
21-Oct-2021
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device
Package Package Pins
Type Drawing
SPQ
Reel
Reel
A0
B0
K0
P1
W
Pin1
Diameter Width (mm) (mm) (mm) (mm) (mm) Quadrant
(mm) W1 (mm)
LM3678SD-1.2/NOPB
LM3678SDE-1.2/NOPB
WSON
WSON
DSC
DSC
10
10
1000
250
178.0
178.0
12.4
12.4
3.3
3.3
3.3
3.3
1.0
1.0
8.0
8.0
12.0
12.0
Q1
Q1
Pack Materials-Page 1
PACKAGE MATERIALS INFORMATION
www.ti.com
21-Oct-2021
*All dimensions are nominal
Device
Package Type Package Drawing Pins
SPQ
Length (mm) Width (mm) Height (mm)
LM3678SD-1.2/NOPB
LM3678SDE-1.2/NOPB
WSON
WSON
DSC
DSC
10
10
1000
250
208.0
208.0
191.0
191.0
35.0
35.0
Pack Materials-Page 2
MECHANICAL DATA
DSC0010A
SDA10A (Rev A)
www.ti.com
IMPORTANT NOTICE AND DISCLAIMER
TI PROVIDES TECHNICAL AND RELIABILITY DATA (INCLUDING DATA SHEETS), DESIGN RESOURCES (INCLUDING REFERENCE
DESIGNS), APPLICATION OR OTHER DESIGN ADVICE, WEB TOOLS, SAFETY INFORMATION, AND OTHER RESOURCES “AS IS”
AND WITH ALL FAULTS, AND DISCLAIMS ALL WARRANTIES, EXPRESS AND IMPLIED, INCLUDING WITHOUT LIMITATION ANY
IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT OF THIRD
PARTY INTELLECTUAL PROPERTY RIGHTS.
These resources are intended for skilled developers designing with TI products. You are solely responsible for (1) selecting the appropriate
TI products for your application, (2) designing, validating and testing your application, and (3) ensuring your application meets applicable
standards, and any other safety, security, regulatory or other requirements.
These resources are subject to change without notice. TI grants you permission to use these resources only for development of an
application that uses the TI products described in the resource. Other reproduction and display of these resources is prohibited. No license
is granted to any other TI intellectual property right or to any third party intellectual property right. TI disclaims responsibility for, and you
will fully indemnify TI and its representatives against, any claims, damages, costs, losses, and liabilities arising out of your use of these
resources.
TI’s products are provided subject to TI’s Terms of Sale or other applicable terms available either on ti.com or provided in conjunction with
such TI products. TI’s provision of these resources does not expand or otherwise alter TI’s applicable warranties or warranty disclaimers for
TI products.
TI objects to and rejects any additional or different terms you may have proposed. IMPORTANT NOTICE
Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265
Copyright © 2021, Texas Instruments Incorporated
相关型号：
SI9130DB
5- and 3.3-V Step-Down Synchronous ConvertersWarning: Undefined variable $rtag in /www/wwwroot/website_ic37/www.icpdf.com/pdf/pdf/index.php on line 217
-
VISHAY
SI9135LG-T1
SMBus Multi-Output Power-Supply ControllerWarning: Undefined variable $rtag in /www/wwwroot/website_ic37/www.icpdf.com/pdf/pdf/index.php on line 217
-
VISHAY
SI9135LG-T1-E3
SMBus Multi-Output Power-Supply ControllerWarning: Undefined variable $rtag in /www/wwwroot/website_ic37/www.icpdf.com/pdf/pdf/index.php on line 217
-
VISHAY
SI9135_11
SMBus Multi-Output Power-Supply ControllerWarning: Undefined variable $rtag in /www/wwwroot/website_ic37/www.icpdf.com/pdf/pdf/index.php on line 217
-
VISHAY
SI9136_11
Multi-Output Power-Supply ControllerWarning: Undefined variable $rtag in /www/wwwroot/website_ic37/www.icpdf.com/pdf/pdf/index.php on line 217
-
VISHAY
SI9130CG-T1-E3
Pin-Programmable Dual Controller - Portable PCsWarning: Undefined variable $rtag in /www/wwwroot/website_ic37/www.icpdf.com/pdf/pdf/index.php on line 217
-
VISHAY
SI9130LG-T1-E3
Pin-Programmable Dual Controller - Portable PCsWarning: Undefined variable $rtag in /www/wwwroot/website_ic37/www.icpdf.com/pdf/pdf/index.php on line 217
-
VISHAY
SI9130_11
Pin-Programmable Dual Controller - Portable PCsWarning: Undefined variable $rtag in /www/wwwroot/website_ic37/www.icpdf.com/pdf/pdf/index.php on line 217
-
VISHAY
SI9137
Multi-Output, Sequence Selectable Power-Supply Controller for Mobile ApplicationsWarning: Undefined variable $rtag in /www/wwwroot/website_ic37/www.icpdf.com/pdf/pdf/index.php on line 217
-
VISHAY
SI9137DB
Multi-Output, Sequence Selectable Power-Supply Controller for Mobile ApplicationsWarning: Undefined variable $rtag in /www/wwwroot/website_ic37/www.icpdf.com/pdf/pdf/index.php on line 217
-
VISHAY
SI9137LG
Multi-Output, Sequence Selectable Power-Supply Controller for Mobile ApplicationsWarning: Undefined variable $rtag in /www/wwwroot/website_ic37/www.icpdf.com/pdf/pdf/index.php on line 217
-
VISHAY
SI9122E
500-kHz Half-Bridge DC/DC Controller with Integrated Secondary Synchronous Rectification DriversWarning: Undefined variable $rtag in /www/wwwroot/website_ic37/www.icpdf.com/pdf/pdf/index.php on line 217
-
VISHAY
©2020 ICPDF网 联系我们和版权申明