June 11, 2008
LM3691
High Accuracy, Miniature 1A, Step-Down DC-DC Converter
for Portable Applications
LM3691 High Accuracy, Miniature 1A, Step-Down DC-DC Converter for Portable Applications
General Description
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.
Typical Application Circuit
Features
V
■
■
■
■
■
■
■
■
■
■
■
= 0.75V to 1.8V
OUT
±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
(V
= 1.8V, ECO Mode)
OUT
30013430
FIGURE 1. Typical Application Circuit
30013454
© 2008 National Semiconductor Corporation 300134 www.national.com
Connection Diagram and Package Mark Information
LM3691
30013406
FIGURE 2. 6-Bump Thin Micro SMD Package, Large Bump
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.
NS Package Number TLA06LCA
Pin Descriptions
Pin Micro SMD Name Description
A1 EN 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.
B1 Mode 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 Ground pin.
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Ordering Information
LM3691
Voltage Option V
0.75 LM3691TL-0.75 V 250 units, Tape-and-Reel
0.85* LM3691TL-0.85 TBD 250 units, Tape-and-Reel
0.9* LM3691TL-0.9 TBD 250 units, Tape-and-Reel
1.0* LM3691TL-1.0 TBD 250 units, Tape-and-Reel
1.1* LM3691TL-1.1 TBD 250 units, Tape-and-Reel
1.2 LM3691TL–1.2 X 250 units, Tape-and-Reel
1.3* LM3691TL–1.3 TBD 250 units, Tape-and-Reel
1.375* LM3691TL–1.375 TBD 250 units, Tape-and-Reel
1.5 LM3691TL–1.5 Y 250 units, Tape-and-Reel
1.6* LM3691TL–1.6 TBD 250 units, Tape-and-Reel
1.8 LM3691TL–1.8 Z 250 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.
Order Number 6–bump Micro
SMD
LM3691TLX–0.75 V 3000 units, Tape-and-Reel
LM3691TLX–0.85 TBD 3000 units, Tape-and-Reel
LM3691TLX–0.9 TBD 3000 units, Tape-and-Reel
LM3691TLX–1.0 TBD 3000 units, Tape-and-Reel
LM3691TLX–1.1 TBD 3000 units, Tape-and-Reel
LM3691TLX–1.2 X 3000 units, Tape-and-Reel
LM3691TLX–1.3 TBD 3000 units, Tape-and-Reel
LM3691TLX–1.375 TBD 3000 units, Tape-and-Reel
LM3691TLX–1.5 Y 3000 units, Tape-and-Reel
LM3691TLX–1.6 TBD 3000 units, Tape-and-Reel
LM3691TLX–1.8 Z 3000 units, Tape-and-Reel
Package Marking Supplied As
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Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
LM3691
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
If Military/Aerospace specified devices are required, please
contact the National Semiconductor Sales Office/Distributors
for availability and specifications.
VIN Pin to GND −0.2V to 6.0V
EN, MODE pin to GND −0.2V to 6.0V
FB, SW pin (GND−0.2V) to
Junction Temperature (T
J-MAX
Storage Temperature Range −65°C to +150°C
Continuous Power Dissipation
(Note 3)
Maximum Lead Temperature
(Soldering, 10 sec.)
ESD Rating (Note 4)
Human Body Model 2 kV
Machine Model 200V
(VIN + 0.2V) w/ 6.0V max
) +150°C
Internally Limited
260°C
Operating Ratings (Notes 1, 2)
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 (Note5)−40°C to +85°C
Thermal Properties
Junction-to-Ambient Thermal
Resistance (θJA) (Note 6)
(micro SMD)
85°C/W
Electrical Characteristics (Notes 2, 7, 8) Limits in standard typeface are for T
= 25°C. Limits in boldface type
A
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 Typ Max Units
V
FB
I
SHDN
I
Q_ECO
I
Q_PWM
R
DSON (P)
R
DSON (N)
I
LIM
V
IH
V
IL
I
EN,MODE
F
SW
V
ON
Feedback Voltage PWM Mode. No load V
PWM Mode. No load V
= 1.1V to 1.8V -1 +1 %
OUT
= 0.75V to 1.0V -10 +10 mV
OUT
Shutdown Supply Current EN = 0V 0.03 1 µA
ECO Mode I
PWM Mode I
q
q
ECO Mode 64 80 µA
PWM Mode 490 600 µA
Pin-Pin Resistance for PFET VIN = VGS = 3.6V, IO = 200 mA 160 250
Pin-Pin Resistance for NFET VIN = VGS = 3.6V, IO = −200 mA 115 180
Switch Peak Current Limit Open loop 1250 1500 1700 mA
Logic High Input 1.2 V
Logic Low Input 0.4 V
Input Current 0.01 1 µA
Switching Frequency PWM Mode 3.6 4 4.4 MHz
UVLO threshold VIN rising 2.2 V
VIN falling 2.1 V
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 T
= 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 (T
the application (P
− (θJAx P
D-MAX
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.
) and the junction to ambient thermal resistance of the package (θJA) in the application, as given by the following equation: T
D-MAX
). Due to the pulsed nature of testing the part, the temp in the Electrical Characteristic table is specified as TA = TJ.
) is dependent on the maximum operating junction temperature (T
A-MAX
), the maximum power dissipation of the device in
J-MAX
A-MAX
= T
mΩ
mΩ
J
J-MAX
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Block Diagram
LM3691
FIGURE 3. Simplified Functional Diagram
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30013431
Typical Performance Characteristics LM3691TL Typical Application Circuit (page 1), V
= 1.8V, TA = 25°, L = 1.0 μH, 2520, (LQM2HP1R0), CIN = C
LM3691
noted.
= 4.7 μF, 0603(1608), 6.3V, (C1608X5R0J475K) unless otherwise
OUT
= 3.6V, V
IN
OUT
Quiescent Supply current vs. Supply Voltage
No Switching (ECO Mode)
30013455
Shutdown Current vs. Temp
(V
= 1.8V)
OUT
Quiescent Supply current vs. Supply Voltage
No Switching (PWM Mode)
30013456
Switching Frequency vs. Temp
(V
= 1.8V, PWM Mode)
OUT
30013457
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30013458
LM3691
Output Voltage vs. Supply Voltage
(V
= 0.75V)
OUT
Output Voltage vs. Output Current
(V
= 0.75V)
OUT
30013459
Output Voltage vs. Supply Voltage
(V
= 1.8V)
OUT
Output Voltage vs. Output Current
(V
= 1.8V)
OUT
30013460
Input Current vs. Output Current
(V
= 0.75V)
OUT
30013461
30013463
30013462
Input Current vs. Output Current
(V
= 1.8V)
OUT
30013464
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LM3691
Efficiency vs. Output Current
(V
= 0.75V, ECO Mode)
OUT
Efficiency vs. Output Current
(V
= 1.8V, ECO Mode)
OUT
30013465
Efficiency vs. Output Current
(V
= 0.75V, FPWM Mode)
OUT
30013467
Load Current Threshold vs. Supply Voltage
(V
= 0.75V, ECO Mode to PWM Mode)
OUT
30013466
Efficiency vs. Output Current
(V
= 1.8V, FPWM Mode)
OUT
30013468
Load Current Threshold vs. Supply Voltage
(V
= 1.8V, ECO Mode to PWM Mode)
OUT
30013469
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30013470
LM3691
Output Voltage Ripple vs. Supply Voltage
(V
= 0.75V)
OUT
30013471
Closed Loop Current Limit vs. Temperature
(V
= 0.75V)
OUT
Output Voltage Ripple vs. Supply Voltage
(V
= 1.8V)
OUT
30013472
Closed Loop Current Limit vs. Temperature
(V
= 1.8V)
OUT
Line Transient Reponse
(V
= 0.75V, PWM Mode)
OUT
30013473
30013475
30013474
Line Transient Reponse
(V
= 1.8V, PWM Mode)
OUT
30013478
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LM3691
(V
Load Transient Reponse
= 0.75V, ECO Mode 1mA to 25 mA)
OUT
(V
Load Transient Reponse
= 0.75V, ECO Mode 25 mA to 1mA)
OUT
Load Transient Reponse
(V
= 1.8V, ECO Mode 1mA to 25 mA)
OUT
Load Transient Reponse
(V
= 0.75V, ECO Mode to PWM Mode)
OUT
30013479
30013481
Load Transient Reponse
(V
= 1.8V, ECO Mode 25 mA to 1mA)
OUT
Load Transient Reponse
(V
= 0.75V, PWM Mode to ECO Mode)
OUT
30013480
30013482
30013483
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30013484
LM3691
Load Transient Reponse
(V
= 1.8V, ECO Mode to PWM Mode)
OUT
Load Transient Reponse
(V
= 0.75V, FPWM Mode)
OUT
30013485
Load Transient Reponse
(V
= 1.8V, PWM Mode to ECO Mode)
OUT
Load Transient Reponse
(V
= 0.75V, FPWM Mode)
OUT
30013486
Load Transient Reponse
(V
= 1.8V, FPWM Mode)
OUT
30013487
30013489
Load Transient Reponse
(V
= 1.8V, FPWM Mode)
OUT
30013488
30013490
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LM3691
Load Transient Reponse
(V
= 0.75V, PWM Mode)
OUT
Load Transient Reponse
(V
= 1.8V, PWM Mode)
OUT
Start Up into ECO Mode
(V
= 1.8V, R
OUT
= 1.8 kΩ)
OUT
Start Up into ECO Mode
(V
= 0.75V, R
OUT
= 750 Ω)
OUT
30013491
30013493
Start Up into PWM Mode
(V
= 1.8V, R
OUT
OUT
= 6 Ω)
Start Up into PWM Mode
(V
= 0.75V, R
OUT
= 2.5 Ω)
OUT
30013492
30013494
30013495
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30013496
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 (I
features include soft-start, under voltage protection, current
SHUTDOWN
overload protection, and thermal shutdown protection. As
shown in Figure 1, only three external power components are
required for implementation.
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–V
second portion of each cycle, the controller turns the PFET
)/L, by storing energy in a magnetic field. During the
OUT
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 –V
OUT
/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.
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.
= 0.03 µA typ.). Additional
LM3691
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.
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.).
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LM3691
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
30013498
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 V
= 1.8V typ.) during soft-start.
OUT
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.
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LM3691
Application Information
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 (I
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 capac-
itance 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:
typ.) bias current over the
LIM
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 guaran-
tee 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 R
can be calculated as:
ESR
and
Voltage peak-to-peak ripple due to capacitance =
Voltage peak-to-peak ripple due to ESR =
V
PP-ESR
= (2 * I
RIPPLE
) * R
ESR
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 (R
temperature dependent); make sure the value used for cal-
ESR
). The R
is frequency dependent (as well as
ESR
culations 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)
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
Model Type Vendor Voltage Rating (V)
4.7 µF for CIN and C
OUT
C1608X5R0J475K Ceramic TDK 6.3 0603 (1608)
C1608X5R1A475K Ceramic TDK 10.0 0603 (1608)
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D.C.R (mΩ)
Case Size
Inch (mm)
MICRO SMD PACKAGE ASSEMBLY AND USE
Use of the Micro SMD package requires specialized board
LM3691
layout, precision mounting and careful re-flow techniques, as
detailed in National Semiconductor Application Note 1112.
Refer to the section Surface Mount Technology (SMD) As-
sembly 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
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.
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Physical Dimensions inches (millimeters) unless otherwise noted
LM3691
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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