NSC LM3691TL-0.9 High accuracy, miniature 1a, step-down dc-dc converter for portable application Datasheet

LM3691
High Accuracy, Miniature 1A, Step-Down DC-DC Converter
for Portable Applications
General Description
Features
The LM3691 step-down DC-DC converter is optimized for
powering ultra-low voltage circuits from a single Li-Ion cell or
3 cell NiMH/NiCd batteries. It provides up to 1A load current,
over an input voltage range from 2.3V to 5.5V. There are several different fixed voltage output options available.
LM3691 has a mode-control pin that allows the user to select
Forced PWM mode or ECO mode that changes modes between gated PWM mode and PWM automatically depending
on the load. In ECO, LM3691 offers superior efficiency and
very low Iq under light load conditions. ECO mode extends the
battery life through reduction of the quiescent current during
light load conditions and system standby.
The LM3691 is available in a 6–bump micro SMD package.
Only three external surface-mount components, a 1μH inductor, a 4.7 μF input capacitor and a 4.7μF output capacitor, are
required.
■
■
■
■
■
■
■
■
■
VOUT = 0.75V to 1.8V
±1% DC output voltage precision
2.3 ≤ VIN ≤ 5.5V
4 MHz switching frequency
64 μA (typ.) quiescent current in ECO mode
1A maximum load capability
Automatic ECO/PWM mode switching
Mode Pin to select ECO/Forced PWM mode
1 μH inductor, 4.7 μF input capacitor (0603(1608) case
size) and 4.7 μF output capacitor (0603(1608) case size)
■ Current overload and thermal shutdown protections
■ Only three tiny surface-mount external components
required (solution size less than 15 mm2)
Applications
■
■
■
■
Mobile Phones
Hand-Held Radios
MP3 players
Portable Hard Disk Drives
Efficiency vs. Output Current
(VOUT = 1.8V, ECO Mode)
Typical Application Circuit
30013430
FIGURE 1. Typical Application Circuit
30013454
© 2008 National Semiconductor Corporation
300134
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LM3691 High Accuracy, Miniature 1A, Step-Down DC-DC Converter for Portable Applications
June 11, 2008
LM3691
Connection Diagram and Package Mark Information
30013406
FIGURE 2. 6-Bump Thin Micro SMD Package, Large Bump
NS Package Number TLA06LCA
Note: The actual physical placement of the package marking will vary from part to part. The package marking “X” designates the
date code; “V” is an NSC internal code for die traceability. Both will vary in production.
Pin Descriptions
Pin Micro SMD
Name
A1
EN
B1
Mode
Description
Enable pin. The device is in shutdown mode when voltage to this pin is <0.4V and enabled
when >1.2V.
Do not leave this pin floating.
Mode Pin: Mode = 1, Forced PWM
Mode = 0, ECO
Do not leave this pin floating.
C1
FB
Feedback analog input. Connect directly to the output filter capacitor. (Figure 1)
A2
VIN
Power supply input. Connect to the input filter capacitor. (Figure 1)
B2
SW
Switching node connection to the internal PFET switch and NFET synchronous rectifier.
C2
GND
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Ground pin.
2
LM3691
Ordering Information
Voltage Option V
0.75
0.85*
0.9*
1.0*
1.1*
1.2
1.3*
1.375*
1.5
1.6*
1.8
Order Number 6–bump Micro
SMD
Package Marking
Supplied As
LM3691TL-0.75
V
250 units, Tape-and-Reel
LM3691TLX–0.75
V
3000 units, Tape-and-Reel
LM3691TL-0.85
TBD
250 units, Tape-and-Reel
LM3691TLX–0.85
TBD
3000 units, Tape-and-Reel
LM3691TL-0.9
TBD
250 units, Tape-and-Reel
LM3691TLX–0.9
TBD
3000 units, Tape-and-Reel
LM3691TL-1.0
TBD
250 units, Tape-and-Reel
LM3691TLX–1.0
TBD
3000 units, Tape-and-Reel
LM3691TL-1.1
TBD
250 units, Tape-and-Reel
LM3691TLX–1.1
TBD
3000 units, Tape-and-Reel
LM3691TL–1.2
X
250 units, Tape-and-Reel
LM3691TLX–1.2
X
3000 units, Tape-and-Reel
LM3691TL–1.3
TBD
250 units, Tape-and-Reel
LM3691TLX–1.3
TBD
3000 units, Tape-and-Reel
LM3691TL–1.375
TBD
250 units, Tape-and-Reel
LM3691TLX–1.375
TBD
3000 units, Tape-and-Reel
LM3691TL–1.5
Y
250 units, Tape-and-Reel
LM3691TLX–1.5
Y
3000 units, Tape-and-Reel
LM3691TL–1.6
TBD
250 units, Tape-and-Reel
LM3691TLX–1.6
TBD
3000 units, Tape-and-Reel
LM3691TL–1.8
Z
250 units, Tape-and-Reel
LM3691TLX–1.8
Z
3000 units, Tape-and-Reel
* If any of the voltage options other than the released voltages are required, please contact the National Semiconductor Sales Office/Distributors for availability.
3
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LM3691
Absolute Maximum Ratings (Note 1)
Operating Ratings
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Input Voltage Range
2.3V to 5.5V
Recommended Load Current
0 mA to 1000 mA
Junction Temperature (TJ) Range
−40°C to +125°C
Ambient Temperature (TA) Range (Note −40°C to +85°C
5)
If Military/Aerospace specified devices are required, please
contact the National Semiconductor Sales Office/Distributors
for availability and specifications.
VIN Pin to GND
EN, MODE pin to GND
FB, SW pin
Junction Temperature (TJ-MAX)
Storage Temperature Range
Continuous Power Dissipation
(Note 3)
Maximum Lead Temperature
(Soldering, 10 sec.)
ESD Rating (Note 4)
Human Body Model
Machine Model
−0.2V to 6.0V
−0.2V to 6.0V
(GND−0.2V) to
(VIN + 0.2V) w/ 6.0V max
+150°C
−65°C to +150°C
Internally Limited
(Notes 1, 2)
Thermal Properties
Junction-to-Ambient Thermal
Resistance (θJA) (Note 6)
(micro SMD)
85°C/W
260°C
2 kV
200V
Electrical Characteristics (Notes 2, 7, 8) Limits in standard typeface are for TA = 25°C. Limits in boldface type
apply over the operating ambient temperature range (−30°C ≤ TA= TJ ≤ +85°C). Unless otherwise noted, specifications apply to
the LM3691 open loop Typical Application Circuit with VIN = EN = 3.6V.
Symbol
Parameter
Condition
Min
PWM Mode. No load VOUT = 1.1V to 1.8V
-1
PWM Mode. No load VOUT = 0.75V to 1.0V
-10
Typ
Max
Units
+1
%
+10
mV
1
µA
64
80
µA
490
600
µA
160
250
mΩ
115
180
mΩ
1500
1700
mA
VFB
Feedback Voltage
ISHDN
Shutdown Supply Current
EN = 0V
IQ_ECO
ECO Mode Iq
ECO Mode
IQ_PWM
PWM Mode Iq
PWM Mode
RDSON (P)
Pin-Pin Resistance for PFET
VIN = VGS = 3.6V, IO = 200 mA
RDSON (N)
Pin-Pin Resistance for NFET
VIN = VGS = 3.6V, IO = −200 mA
ILIM
Switch Peak Current Limit
Open loop
VIH
Logic High Input
VIL
Logic Low Input
IEN,MODE
Input Current
FSW
Switching Frequency
PWM Mode
VON
UVLO threshold
VIN rising
2.2
V
VIN falling
2.1
V
0.03
1250
V
1.2
3.6
0.4
V
0.01
1
µA
4
4.4
MHz
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the component may occur. Operating Ratings are conditions under which operation
of the device is guaranteed. Operating Ratings do not imply guaranteed performance limits. For guaranteed performance limits and associated test conditions,
see the Electrical Characteristics tables.
Note 2: All voltages are with respect to the potential at the GND pin.
Note 3: 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.).
Note 4: The Human body model is a 100 pF capacitor discharged through a 1.5 kΩ resistor into each pin. The machine model is a 200 pF capacitor discharged
directly into each pin. MIL-STD-883 3015.7
Note 5: In applications where high power dissipation and/or poor package resistance is present, the maximum ambient temperature may have 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). Due to the pulsed nature of testing the part, the temp in the Electrical Characteristic table is specified as TA = TJ.
Note 6: 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.
Note 7: Min and Max limits are guaranteed by design, test or statistical analysis. Typical numbers are not guaranteed, but do represent the most likely norm.
Note 8: The parameters in the electrical characteristic table are tested under open loop conditions at VIN = 3.6V unless otherwise specified. For performance
over the input voltage range and closed loop condition, refer to the datasheet curves.
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LM3691
Block Diagram
30013431
FIGURE 3. Simplified Functional Diagram
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LM3691
Typical Performance Characteristics LM3691TL Typical Application Circuit (page 1), VIN = 3.6V, VOUT
= 1.8V, TA = 25°, L = 1.0 μH, 2520, (LQM2HP1R0), CIN = COUT = 4.7 μF, 0603(1608), 6.3V, (C1608X5R0J475K) unless otherwise
noted.
Quiescent Supply current vs. Supply Voltage
No Switching (ECO Mode)
Quiescent Supply current vs. Supply Voltage
No Switching (PWM Mode)
30013455
30013456
Shutdown Current vs. Temp
(VOUT = 1.8V)
Switching Frequency vs. Temp
(VOUT = 1.8V, PWM Mode)
30013457
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30013458
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LM3691
Output Voltage vs. Supply Voltage
(VOUT = 0.75V)
Output Voltage vs. Supply Voltage
(VOUT = 1.8V)
30013459
30013460
Output Voltage vs. Output Current
(VOUT = 0.75V)
Output Voltage vs. Output Current
(VOUT = 1.8V)
30013461
30013462
Input Current vs. Output Current
(VOUT = 0.75V)
Input Current vs. Output Current
(VOUT = 1.8V)
30013463
30013464
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LM3691
Efficiency vs. Output Current
(VOUT = 0.75V, ECO Mode)
Efficiency vs. Output Current
(VOUT = 1.8V, ECO Mode)
30013465
30013466
Efficiency vs. Output Current
(VOUT = 0.75V, FPWM Mode)
Efficiency vs. Output Current
(VOUT = 1.8V, FPWM Mode)
30013467
30013468
Load Current Threshold vs. Supply Voltage
(VOUT = 0.75V, ECO Mode to PWM Mode)
Load Current Threshold vs. Supply Voltage
(VOUT = 1.8V, ECO Mode to PWM Mode)
30013469
30013470
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LM3691
Output Voltage Ripple vs. Supply Voltage
(VOUT = 0.75V)
Output Voltage Ripple vs. Supply Voltage
(VOUT = 1.8V)
30013471
30013472
Closed Loop Current Limit vs. Temperature
(VOUT = 0.75V)
Closed Loop Current Limit vs. Temperature
(VOUT = 1.8V)
30013473
30013474
Line Transient Reponse
(VOUT = 0.75V, PWM Mode)
Line Transient Reponse
(VOUT = 1.8V, PWM Mode)
30013475
30013478
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LM3691
Load Transient Reponse
(VOUT = 0.75V, ECO Mode 1mA to 25 mA)
Load Transient Reponse
(VOUT = 0.75V, ECO Mode 25 mA to 1mA)
30013479
30013480
Load Transient Reponse
(VOUT = 1.8V, ECO Mode 1mA to 25 mA)
Load Transient Reponse
(VOUT = 1.8V, ECO Mode 25 mA to 1mA)
30013481
30013482
Load Transient Reponse
(VOUT = 0.75V, ECO Mode to PWM Mode)
Load Transient Reponse
(VOUT = 0.75V, PWM Mode to ECO Mode)
30013483
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30013484
10
LM3691
Load Transient Reponse
(VOUT = 1.8V, ECO Mode to PWM Mode)
Load Transient Reponse
(VOUT = 1.8V, PWM Mode to ECO Mode)
30013485
30013486
Load Transient Reponse
(VOUT = 0.75V, FPWM Mode)
Load Transient Reponse
(VOUT = 0.75V, FPWM Mode)
30013487
30013488
Load Transient Reponse
(VOUT = 1.8V, FPWM Mode)
Load Transient Reponse
(VOUT = 1.8V, FPWM Mode)
30013489
30013490
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LM3691
Load Transient Reponse
(VOUT = 0.75V, PWM Mode)
Load Transient Reponse
(VOUT = 1.8V, PWM Mode)
30013491
30013492
Start Up into ECO Mode
(VOUT = 1.8V, ROUT = 1.8 kΩ)
Start Up into PWM Mode
(VOUT = 1.8V, ROUT = 6 Ω)
30013494
30013493
Start Up into ECO Mode
(VOUT = 0.75V, ROUT = 750 Ω)
Start Up into PWM Mode
(VOUT = 0.75V, ROUT = 2.5 Ω)
30013495
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30013496
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LM3691
Operation Description
DEVICE INFORMATION
The LM3691, a high-efficiency, step-down DC-DC switching
buck converter, delivers a constant voltage from either a single Li-Ion or three cell NiMH/NiCd battery to portable devices
such as cell phones and PDAs. Using a voltage mode architecture with synchronous rectification, the LM3691 has the
ability to deliver up to 1000 mA depending on the input voltage
and output voltage, ambient temperature, and the inductor
chosen.
There are three modes of operation depending on the current
required - PWM (Pulse Width Modulation), ECO, and shutdown. The device operates in PWM mode at load currents of
approximately 50 mA (typ.) or higher. Lighter output current
loads cause the device to automatically switch into ECO
mode for reduced current consumption and a longer battery
life. Shutdown mode turns off the device, offering the lowest
current consumption (ISHUTDOWN = 0.03 µA typ.). Additional
features include soft-start, under voltage protection, current
overload protection, and thermal shutdown protection. As
shown in Figure 1, only three external power components are
required for implementation.
30013497
FIGURE 4. Typical PWM Operation
Internal Synchronous Rectification
While in PWM mode, the LM3691 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.
CIRCUIT OPERATION
The LM3691 operates as follows. During the first portion of
each switching cycle, the control block in the LM3691 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 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.
Current Limiting
A current limit feature allows the LM3691 to protect itself and
external components during overload conditions. PWM mode
implements current limit using an internal comparator that
trips at 1500 mA (typ). If the output is shorted to ground and
output voltage becomes lower than 0.3V (typ.), the device
enters a timed current limit mode where the switching frequency will be one fourth, and NFET synchronous rectifier is
disabled, thereby preventing excess current and thermal runaway.
ECO OPERATION
Setting mode pin low places the LM3691 in Auto mode. By
doing so the part switches from ECO (ECOnomy) state to
FPWM (Forced Pulse Width Modulation) state based on output load current. At light loads (less than 50 mA), the converter
enters ECO mode. In this mode the part operates with low Iq.
During ECO operation, the converter positions the output
voltage slightly higher (+30 mV typ.) than the nominal output
voltage in FPWM operation. Because the reference is set
higher, the output voltage increases to reach the target voltage when the part goes from sleep state to switching state.
Once this voltage is reached the converter enters sleep mode,
thereby reducing switching losses and improving light load
efficiency. The output voltage ripple is slightly higher in ECO
mode (30 mV peak–peak ripple typ.).
PWM OPERATION
During PWM operation, the converter operates as a voltagemode controller with input voltage feed forward. This allows
the converter to achieve excellent 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. While in PWM
mode, 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.
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LM3691
switch, reference, control and bias circuitry of the LM3691 are
turned off. Setting EN high (>1.2V) enables normal operation.
When turning on the device with EN soft-start is activated. EN
pin should be set low to turn off the LM3691 during system
power up and under-voltage conditions when the supply is
less than 2.3V. Do not leave the EN pin floating.
SOFT-START
The LM3691 has a soft-start circuit that limits in-rush current
during start-up. Output voltage increase rate is 30 mV/µsec
(at VOUT = 1.8V typ.) during soft-start.
THERMAL SHUTDOWN PROTECTION
The LM3691 has a thermal overload protection function that
operates to protect itself from short-term misuse and overload
conditions. When the junction temperature exceeds around
150°C, the device inhibits operation. Both the PFET and the
NFET are turned off. When the temperature drops below 130°
C, normal operation resumes. Prolonged operation in thermal
overload conditions may damage the device and is considered bad practice.
30013498
FIGURE 5. Typical ECO Operation
FORCED PWM MODE
Setting Mode pin high (>1.2V) places the LM3691 in Forced
PWM. The part is in forced PWM regardless of the load.
SHUTDOWN MODE
Setting the EN input pin low (<0.4V) places the LM3691 in
shutdown mode. During shutdown the PFET switch, NFET
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INDUCTOR SELECTION
DC bias current characteristics of inductors must be considered. Different manufacturers follow different saturation current rating specifications, so attention must be given to
details. DC bias curves should be requested from them as
part of the inductor selection process.
Minimum value of inductance to guarantee good performance is 0.5 µH at 1.5A (ILIM typ.) bias current over the
ambient temp range. The inductor’s DC resistance should
be less than 0.1Ω for good efficiency at high current condition.
The inductor AC loss (resistance) also affects conversion efficiency. Higher Q factor at switching frequency usually gives
better efficiency at light load to middle load.
Table 1 lists suggested inductors and suppliers
INPUT CAPACITOR SELECTION
A ceramic input capacitor of 4.7 µF, 6.3V/10V is sufficient for
most applications. Place the input capacitor as close as possible to the VIN pin and GND pin of the device. A larger value
or higher voltage rating may be used to improve input voltage
filtering. Use X7R, X5R or B types; do not use Y5V or F. DC
bias characteristics of ceramic capacitors must be considered
when selecting case sizes like 0402. Minimum input capacitance to guarantee good performance is 2.2 µF at maximum input voltage DC bias including tolerances and over
ambient temp range.
The input filter capacitor supplies current to the PFET (highside) switch 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 an input filter capacitor with sufficient ripple current rating.
The input current ripple can be calculated as:
Voltage peak-to-peak ripple due to ESR =
VPP-ESR = (2 * IRIPPLE) * RESR
Because these two components are out of phase the rms value can be used to get an approximate value of peak-to-peak
ripple.
Voltage peak-to-peak ripple, root mean squared =
Note that the output voltage ripple is dependent on the 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.
Table 2 lists suggested capacitors and suppliers.
TABLE 1. Suggested Inductors and Their Suppliers
Model
Vendor
Dimensions LxWxH (mm)
D.C.R (mΩ)
LQM2HPN1R0MG0
Murata
2.5 x 2.0 x 1.0
55
MLP2520S1R0L
TDK
2.5 x 2.0 x 1.0
60
KSLI252010AG1R0
HItachi Metals
2.5 x 2.0 x 1.0
80
MIPSZ2012D1R0
FDK
2.0 x 1.25 x 1.0
90
TABLE 2. Suggested Capacitors and Their Suppliers
Type
Vendor
Voltage Rating (V)
Case Size
Inch (mm)
C1608X5R0J475K
Ceramic
TDK
6.3
0603 (1608)
C1608X5R1A475K
Ceramic
TDK
10.0
0603 (1608)
Model
4.7 µF for CIN and COUT
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LM3691
OUTPUT CAPACITOR SELECTION
Use a 4.7μF, 6.3V ceramic capacitor, X7R, X5R or B types;
do not use Y5V or F. DC bias voltage characteristics of ceramic capacitors must be considered. 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. Minimum output capacitance to guarantee good performance is 2.2 µF at the output voltage DC
bias including tolerances and over ambient temp range.
The output voltage ripple is caused by the charging and discharging of the output capacitor and also due to its RESR and
can be calculated as:
Voltage peak-to-peak ripple due to capacitance =
Application Information
LM3691
corners. Initially, the trace to each pad should be 7 mil wide,
for a section approximately 7 mil long or longer, as a thermal
relief. Then each trace should neck up or down to its optimal
width. The important criteria is symmetry. This ensures the
solder bumps on the LM3691 re-flow evenly and that the device solders level to the board. In particular, special attention
must be paid to the pads for bumps A2 and C2, because GND
and VIN are typically connected to large copper planes.
The micro SMD package is optimized for the smallest possible size in applications with red or infrared opaque cases.
Because the micro SMD package lacks the plastic encapsulation characteristic of larger devices, it is vulnerable to light.
Backside metallization and/or epoxy coating, along with front
side shading by the printed circuit board, reduce this sensitivity. However, the package has exposed die edges. In particular, micro SMD devices are sensitive to light, in the red
and infrared range, shining on the package’s exposed die
edges.
MICRO SMD PACKAGE ASSEMBLY AND USE
Use of the Micro SMD package requires specialized board
layout, precision mounting and careful re-flow techniques, as
detailed in National Semiconductor Application Note 1112.
Refer to the section Surface Mount Technology (SMD) Assembly Considerations. For best results in assembly, alignment ordinals on the PC board should be used to facilitate
placement of the device. The pad style used with micro SMD
package must be the NSMD (Non-Solder Mask Defined) type.
This means that the solder-mask opening is larger than the
pad size. This prevents a lip that otherwise forms if the soldermask and pad overlap, from holding the device off the surface
of the board and interfering with mounting. See Application
Note 1112 for specific instructions how to do this.
The 6-bump package used for LM3691 has 300–micron solder balls and requires 10.82 mils pads for mounting on the
circuit board. The trace to each pad should enter the pad with
a 90° entry angle to prevent debris from being caught in deep
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LM3691
Physical Dimensions inches (millimeters) unless otherwise noted
6–bump Thin Micro SMD, Large Bump
NS Package Number TLA06LCA
X1 = 1.260mm ± 0.030mm
X2 = 1.565mm ± 0.030mm
X3 = 0.600mm ± 0.075mm
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LM3691 High Accuracy, Miniature 1A, Step-Down DC-DC Converter for Portable Applications
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www.national.com/tempsensors
Wireless (PLL/VCO)
www.national.com/wireless
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