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LM2733
SNVS209G – NOVEMBER 2002 – REVISED MAY 2019
LM2733 0.6- and 1.6-MHz Boost Converters With 40-V Internal FET Switch in SOT-23
1 Features
3 Description
•
•
•
•
•
•
•
•
•
•
The LM2733 switching regulators are current-mode
boost converters operating fixed frequency of 1.6
MHz (“X” option) and 600 kHz (“Y” option).
1
40-V DMOS FET switch
1.6-MHz (“X”), 0.6 MHz (“Y”) Switching frequency
Low RDS(ON) DMOS FET
Switch current up to 1 A
Wide input voltage 2.7 V to 14 V
Low shutdown current (< 1 µA)
5-Pin SOT-23 package
Uses tiny capacitors and inductors
Cycle-by-cycle current limiting
Internally compensated
These parts have a logic-level shutdown pin that can
be used to reduce quiescent current and extend
battery life.
Protection is provided through cycle-by-cycle current
limiting and thermal shutdown. Internal compensation
simplifies design and reduces component count.
2 Applications
•
•
•
•
•
The use of SOT-23 package, made possible by the
minimal power loss of the internal 1-A switch and use
of small inductors and capacitors, results in the
industry's highest power density. The 40-V internal
switch makes these solutions perfect for boosting to
voltages of 16 V or greater.
White LED current source
PDAs and palm-top computers
Digital cameras
Portable phones and games
Local boost regulator
Device Information(1)
PART NUMBER
LM2733
PACKAGE
BODY SIZE (NOM)
SOT-23 (5)
2.90 mm × 1.60 mm
(1) For all available packages, see the orderable addendum at
the end of the data sheet.
Typical Application Circuit
VIN
SHDN
R3
51KQ
U1
SW
LM2733 ³;´
SHDN
GND
GND
D1
MBR0520
L1/10PH
5 VIN
C1
2.2PF
Efficiency vs. Load Current
R1/117KQ
FB
R2
13.3KQ
CF
220pF
12V
OUT
330mA
(TYP)
C2
4.7PF
1
An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.
LM2733
SNVS209G – NOVEMBER 2002 – REVISED MAY 2019
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Table of Contents
1
2
3
4
5
6
7
Features ..................................................................
Applications ...........................................................
Description .............................................................
Revision History.....................................................
Pin Configuration and Functions .........................
Specifications.........................................................
1
1
1
2
3
3
6.1
6.2
6.3
6.4
6.5
6.6
3
3
4
4
4
6
Absolute Maximum Ratings ......................................
ESD Ratings..............................................................
Recommended Operating Conditions.......................
Thermal Information ..................................................
Electrical Characteristics...........................................
Typical Characteristics ..............................................
7.3 Feature Description................................................. 10
7.4 Device Functional Modes........................................ 11
8
Application and Implementation ........................ 12
8.1 Application Information............................................ 12
8.2 Typical Application .................................................. 12
9 Power Supply Recommendations...................... 18
10 Layout................................................................... 18
10.1 Layout Guidelines ................................................. 18
10.2 Layout Example .................................................... 18
11 Device and Documentation Support ................. 19
Detailed Description ............................................ 10
11.1 Trademarks ........................................................... 19
11.2 Electrostatic Discharge Caution ............................ 19
11.3 Glossary ................................................................ 19
7.1 Overview ................................................................. 10
7.2 Functional Block Diagram ....................................... 10
12 Mechanical, Packaging, and Orderable
Information ........................................................... 19
4 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision F (December 2014) to Revision G
•
Changed Typical Application Circuit image to correct rogue connector lines. ...................................................................... 1
Changes from Revision E (April 2013) to Revision F
•
2
Page
Added Pin Configuration and Functions section, ESD Ratings table, Feature Description section, Device Functional
Modes, Application and Implementation section, Power Supply Recommendations section, Layout section, Device
and Documentation Support section, and Mechanical, Packaging, and Orderable Information section .............................. 1
Changes from Revision D (April 2013) to Revision E
•
Page
Page
Changed layout of National Semiconductor Data Sheet to TI format .................................................................................. 11
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SNVS209G – NOVEMBER 2002 – REVISED MAY 2019
5 Pin Configuration and Functions
5-Pin DBV
SOT-23 Package
Top View
Pin Functions
PIN
NAME
NO.
I/O
DESCRIPTION
SW
1
O
GND
2
GND
Drain of the internal FET switch.
FB
3
I
Feedback point that connects to external resistive divider.
SHDN
4
I
Shutdown control input. Connect to VIN if this feature is not used.
VIN
5
I
Analog and power input.
Analog and power ground.
6 Specifications
6.1 Absolute Maximum Ratings (1) (2)
MIN
MAX
UNIT
Input supply voltage (VIN)
−0.4
14.5
V
FB pin voltage
−0.4
6
V
SW pin voltage
−0.4
40
V
SHDN pin voltage
−0.4
VIN + 0.3
V
Power dissipation (3)
Internally Limited
Lead temperature (soldering, 5 sec.)
−65
Storage temperature,Tstg
(1)
(2)
(3)
300
°C
150
°C
Absolute Maximum Ratings indicate limits beyond which damage to the component may occur. Electrical specifications do not apply
when operating the device outside of the limits set forth under the operating ratings which specify the intended range of operating
conditions.
If Military/Aerospace specified devices are required, contact the Texas Instruments Sales Office/ Distributors for availability and
specifications.
The maximum power dissipation which can be safely dissipated for any application is a function of the maximum junction temperature,
TJ(MAX) = 125°C, the junction-to-ambient thermal resistance for the SOT-23 package, RθJ-A = 210°C/W, and the ambient temperature,
TA. The maximum allowable power dissipation at any ambient temperature for designs using this device can be calculated using the
formula:
If power dissipation exceeds the maximum specified above, the internal thermal protection
circuitry protects the device by reducing the output voltage as required to maintain a safe junction temperature.
6.2 ESD Ratings
VALUE
V(ESD)
(1)
Electrostatic discharge
Human body model (HBM), per ANSI/ESDA/JEDEC JS-001, all pins
Machine model
(1)
UNIT
±2000
±200
V
JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
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6.3 Recommended Operating Conditions
over operating free-air temperature range (unless otherwise noted)
MIN
Input supply voltage (VIN)
SHDN pin voltage
Junction temperature
MAX
UNIT
2.7
14
0
VIN
V
V
−40
125
°C
6.4 Thermal Information
LM2733
THERMAL METRIC (1)
DBV (SOT-23)
UNIT
5 PINS
RθJA
Junction-to-ambient thermal resistance
210
°C/W
RθJC(top)
Junction-to-case (top) thermal resistance
122
°C/W
RθJB
Junction-to-board thermal resistance
38.4
°C/W
ψJT
Junction-to-top characterization parameter
12.8
°C/W
ψJB
Junction-to-board characterization parameter
37.5
°C/W
RθJC(bot)
Junction-to-case (bottom) thermal resistance
n/a
°C/W
(1)
For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal MetricsSPRA953
application report.
6.5 Electrical Characteristics
Unless otherwise specified: VIN = 5 V, VSHDN = 5 V, IL = 0 A, TJ = 25°C.
PARAMETER
TEST CONDITIONS
VIN
Input voltage
−40°C ≤ TJ ≤ +125°C
ISW
Switch current limit
See (3)
RDS(ON)
Switch ON resistance
ISW = 100 mA
SHDNTH
Shutdown threshold
Device ON, −40°C ≤ TJ ≤ +125°C
ISHDN
Shutdown pin bias current
MIN (1)
TYP (2)
2.7
1
500
Feedback pin reference voltage
IFB
Feedback pin bias current
VSHDN = 0
0
VSHDN = 5 V
0
Quiescent current
60
VSHDN = 5 V, Switching "X"
2.1
(1)
(2)
(3)
4
2.7 V ≤ VIN ≤ 14 V
µA
V
nA
mA
1.1
VSHDN = 5 V, Switching "Y",
−40°C ≤ TJ ≤ +125°C
VSHDN = 0
FB voltage line regulation
V
3
2
400
VSHDN = 5 V, Not Switching,
−40°C ≤ TJ ≤ +125°C
Δ VFBΔVIN
0.50
A
1.255
VFB = 1.23 V
VSHDN = 5 V, Not Switching
mΩ
1.230
1.205
VSHDN = 5 V, Switching "X",
−40°C ≤ TJ ≤ +125°C
IQ
650
2
VIN = 3 V
VSHDN = 5 V, Switching "Y"
V
1.5
Device OFF, −40°C ≤ TJ ≤
+125°C
VIN = 3 V, −40°C ≤ TJ ≤ +125°C
UNIT
14
1.5
VSHDN = 5 V, −40°C ≤ TJ ≤
+125°C
VFB
MAX (1)
500
0.024
0.02
µA
1
%/V
Limits are specified by testing, statistical correlation, or design.
Typical values are derived from the mean value of a large quantity of samples tested during characterization and represent the most
likely expected value of the parameter at room temperature.
Switch current limit is dependent on duty cycle (see Typical Characteristics). Limits shown are for duty cycles ≤ 50%.
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Electrical Characteristics (continued)
Unless otherwise specified: VIN = 5 V, VSHDN = 5 V, IL = 0 A, TJ = 25°C.
PARAMETER
TEST CONDITIONS
MIN (1)
“X” Option
FSW
Switching frequency
“X” Option, −40°C ≤ TJ ≤ +125°C
Maximum duty cycle
IL
Switch leakage
“X” Option, −40°C ≤ TJ ≤ +125°C
0.40
Not Switching VSW = 5 V
UNIT
MHz
0.8
93%
87%
“Y” Option
“Y” Option, −40°C ≤ TJ ≤ +125°C
1.85
0.60
“X” Option
DMAX
MAX (1)
1.6
1.15
“Y” Option
“Y” Option, −40°C ≤ TJ ≤ +125°C
TYP (2)
96%
93%
1
µA
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6.6 Typical Characteristics
Unless otherwise specified: VIN = 5 V, SHDN pin is tied to VIN.
1.06
1.05
Iq ACTIVE (mA)
1.04
1.03
1.02
1.01
1
0.99
0.98
-50
-25
0
25
50
75
100 125 150
o
TEMPERATURE ( C)
Figure 2. Iq VIN (Active) vs Temperature - "Y"
Figure 1. Iq VIN (Active) vs Temperature - "X"
0.615
OSCILLATOR FREQUENCY (MHz)
0.610
0.605
0.600
0.595
0.590
0.585
0.580
0.575
-50
-25
0
25
50
75
100 125 150
TEMPERATURE (oC)
Figure 3. Oscillator Frequency vs Temperature - "X"
Figure 4. Oscillator Frequency vs Temperature - "Y"
93.4
96.55
96.5
93.3
93.2
MAX DUTY CYCLE
MAX DUTY CYCLE (%)
96.45
93.1
93.0
92.9
96.4
96.35
96.3
96.25
96.2
96.15
92.8
96.1
92.7
-40
96.05
-25
0
25
50
75
100
125
0
25
50
75
100 125 150
TEMPERATURE (oC)
TEMPERATURE (oC)
Figure 5. Max. Duty Cycle vs Temperature - "X"
6
-50 -25
Figure 6. Max. Duty Cycle vs Temperature - "Y"
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Typical Characteristics (continued)
Unless otherwise specified: VIN = 5 V, SHDN pin is tied to VIN.
Figure 7. Feedback Voltage vs Temperature
Figure 8. RDS(ON) vs Temperature
Figure 9. Current Limit vs Temperature
Figure 10. RDS(ON) vs VIN
100
90
VIN = 10V
EFFICIENCY (%)
80
VIN = 5V
70
60
VIN = 3.3V
50
40
30
20
10
0
0
200
400
600
800
1000
LOAD CURRENT (mA)
Figure 11. Efficiency vs Load Current (VOUT = 12 V) - "X"
Figure 12. Efficiency vs Load Current (VOUT = 15 V) - "X"
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Typical Characteristics (continued)
Unless otherwise specified: VIN = 5 V, SHDN pin is tied to VIN.
100
100
90
90
VIN = 10V
VIN = 5V
70
VIN = 3.3V
60
VIN = 10V
80
EFFICIENCY (%)
EFFICIENCY (%)
80
50
40
70
60
50
40
30
30
20
20
10
10
0
VIN = 5V
0
0
100
200
300 400
500
600 700
0
50
LOAD CURRENT (mA)
LOAD CURRENT (mA)
Figure 13. Efficiency vs Load Current (VOUT = 20 V) - "X"
Figure 14. Efficiency vs Load Current (VOUT = 25 V) - "X"
100
100
90
90
VIN = 10V
80
EFFICIENCY (%)
80
EFFICIENCY (%)
100 150 200 250 300 350 400
70
VIN = 5V
60
50
40
30
VIN = 10V
70
60
50
40
30
20
20
10
10
0
0
50
100
150
200
250
0
300 350
0
LOAD CURRENT (mA)
50
100
150
200
LOAD CURRENT (mA)
Figure 15. Efficiency vs Load Current (VOUT = 30 V) - "X"
Figure 16. Efficiency vs Load Current (VOUT = 35 V) - "X"
90
80
VIN=10V
EFFICIENCY (%)
70
60
50
40
30
20
10
0
0
50
100
150
200
LOAD CURRENT (mA)
Figure 17. Efficiency vs Load Current (VOUT = 40 V) - "X"
8
Figure 18. Efficiency vs Load (VOUT = 15 V) - "Y"
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Typical Characteristics (continued)
Unless otherwise specified: VIN = 5 V, SHDN pin is tied to VIN.
Figure 19. Efficiency vs Load (VOUT = 20 V) - "Y"
Figure 20. Efficiency vs Load (VOUT = 25 V) - "Y"
Figure 21. Efficiency vs Load (VOUT = 30 V) - "Y"
Figure 22. Efficiency vs Load (VOUT = 35 V) - "Y"
Figure 23. Efficiency vs Load (VOUT = 40 V) - "Y"
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7 Detailed Description
7.1 Overview
The LM2733 device is a switching converter IC that operates at a fixed frequency (0.6 or 1.6 MHz) using currentmode control for fast transient response over a wide input voltage range and incorporate pulse-by-pulse current
limiting protection. Because this is current mode control, a 50 mΩ sense resistor in series with the switch FET is
used to provide a voltage (which is proportional to the FET current) to both the input of the pulse width
modulation (PWM) comparator and the current limit amplifier.
At the beginning of each cycle, the S-R latch turns on the FET. As the current through the FET increases, a
voltage (proportional to this current) is summed with the ramp coming from the ramp generator and then fed into
the input of the PWM comparator. When this voltage exceeds the voltage on the other input (coming from the
Gm amplifier), the latch resets and turns the FET off. Since the signal coming from the Gm amplifier is derived
from the feedback (which samples the voltage at the output), the action of the PWM comparator constantly sets
the correct peak current through the FET to keep the output volatge in regulation.
Q1 and Q2 along with R3 - R6 form a bandgap voltage reference used by the IC to hold the output in regulation.
The currents flowing through Q1 and Q2 will be equal, and the feedback loop will adjust the regulated output to
maintain this. Because of this, the regulated output is always maintained at a voltage level equal to the voltage at
the FB node "multiplied up" by the ratio of the output resistive divider.
The current limit comparator feeds directly into the flip-flop, that drives the switch FET. If the FET current reaches
the limit threshold, the FET is turned off and the cycle terminated until the next clock pulse. The current limit
input terminates the pulse regardless of the status of the output of the PWM comparator.
7.2 Functional Block Diagram
7.3 Feature Description
7.3.1 Switching Frequency
The LM2733 device is provided with two switching frequencies: the “X” version is typically 1.6 MHz, while the “Y”
version is typically 600 kHz. The best frequency for a specific application must be determined based on the
tradeoffs involved. See Switching Frequency in the Detailed Design Procedure section.
10
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7.4 Device Functional Modes
7.4.1 Shutdown Pin Operation
The device is turned off by pulling the shutdown pin low. If this function is not going to be used, tie the pin
directly to VIN. If the SHDN function is needed, a pullup resistor must be used to VIN (approximately 50 k to 100
kΩ recommended). The SHDN pin must not be left unterminated.
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8 Application and Implementation
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
8.1 Application Information
The LM2733 device is a high frequency switching boost regulator that offers small size and high power
conversion efficiency. The "X" version of the part operates at 1.6 MHz switching frequency and the "Y" version at
600 kHz.
The LM2733 device targets applications with high output voltages and uses a high voltage FET allowing switch
currents up to 1 A. The LM2731 device is similar to the LM2733 device but has a lower voltage FET allowing
switch currents up to 1.8 A.
8.2 Typical Application
Figure 24. Basic Application Circuit
8.2.1 Design Requirements
Table 1. Circuit Configurations
LM2733-X
LM2733-X
LM2733-Y
COMPONENT
LOW VOLTAGE 5-12 V 330 mA
typical
HIGH VOLTAGE 20 V 170 mA
typical
HIGH VOLTAGE 30 V 110 mA
typical
R1
117 K
205 K
309 K
13.3 K
R2
13.3 K
13.3 K
Cf
220 pF
120 pF
82 pF
D1
MBR0520
MBR0530
MBR0540
8.2.2 Detailed Design Procedure
8.2.2.1 Selecting the External Capacitors
The best capacitors for use with the LM2733 device are multi-layer ceramic capacitors. They have the lowest
ESR (equivalent series resistance) and highest resonance frequency which makes them optimum for use with
high frequency switching converters.
When selecting a ceramic capacitor, use only X5R and X7R dielectric types. Other types such as Z5U and Y5F
have such severe loss of capacitance due to effects of temperature variation and applied voltage, they may
provide as little as 20% of rated capacitance in many typical applications. Always consult capacitor
manufacturer’s data curves before selecting a capacitor. High-quality ceramic capacitors can be obtained from
Taiyo-Yuden, AVX, and Murata.
12
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8.2.2.2 Selecting the Output Capacitor
A single ceramic capacitor of value 4.7 µF to 10 µF provides sufficient output capacitance for most applications.
For output voltages below 10 V, a 10-µF capacitance is required. If larger amounts of capacitance are desired for
improved line support and transient response, tantalum capacitors can be used in parallel with the ceramics.
Aluminum electrolytics with ultra-low ESR such as Sanyo Oscon can be used, but are usually prohibitively
expensive. Typical AI electrolytic capacitors are not suitable for switching frequencies above 500 kHz due to
significant ringing and temperature rise due to self-heating from ripple current. An output capacitor with excessive
ESR can also reduce phase margin and cause instability.
8.2.2.3 Selecting the Input Capacitor
An input capacitor is required to serve as an energy reservoir for the current which must flow into the coil each
time the switch turns ON. This capacitor must have extremely low ESR, so ceramic is the best choice. TI
recommends a nominal value of 2.2 µF, but larger values can be used. Because this capacitor reduces the
amount of voltage ripple detected at the input pin, it also reduces the amount of EMI passed back along that line
to other circuitry.
8.2.2.4 Feedforward Compensation
Although internally compensated, the feedforward capacitor Cf is required for stability (see Figure 24). Adding
this capacitor puts a zero in the loop response of the converter. Without it, the regulator loop can oscillate. The
recommended frequency for the zero fz is approximately 8 kHz. Cf can be calculated using the formula:
Cf = 1 / (2 X π X R1 X fz)
(1)
8.2.2.5 Selecting Diodes
The external diode used in the typical application should be a Schottky diode. If the switch voltage is less than 15
V, a 20-V diode such as the MBR0520 is recommended. If the switch voltage is between 15 V and 25 V, TI
recommends a 30-V diode such as the MBR0530. If the switch voltage exceeds 25 V, a 40-V diode such as the
MBR0540 should be used.
The MBR05XX series of diodes are designed to handle a maximum average current of 0.5 A. For applications
exceeding 0.5 A average but less than 1 A, a Microsemi UPS5817 can be used.
8.2.2.6 Setting the Output Voltage
The output voltage is set using the external resistors R1 and R2 (see Figure 24). A value of approximately 13.3
kΩ is recommended for R2 to establish a divider current of approximately 92 µA. R1 is calculated using the
formula:
R1 = R2 X (VOUT/1.23 − 1)
(2)
8.2.2.7 Switching Frequency
The device options provide for two fixed frequency operating conditions 1.6 MHz, and 600 kHz. Chose the
operating frequency required noting the following trade-offs:
Higher switching frequency means the inductors and capacitors can be made smaller and cheaper for a given
output voltage and current. The down side is that efficiency is slightly lower because the fixed switching losses
occur more frequently and become a larger percentage of total power loss. EMI is typically worse at higher
switching frequencies because more EMI energy will be seen in the higher frequency spectrum where most
circuits are more sensitive to such interference.
8.2.2.8 Duty Cycle
The maximum duty cycle of the switching regulator determines the maximum boost ratio of output-to-input
voltage that the converter can attain in continuous mode of operation. The duty cycle for a given boost
application is defined as:
VOUT + VDIODE - VIN
Duty Cycle =
VOUT + VDIODE - VSW
(3)
This applies for continuous mode operation.
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The equation shown for calculating duty cycle incorporates terms for the FET switch voltage and diode forward
voltage. The actual duty cycle measured in operation will also be affected slightly by other power losses in the
circuit such as wire losses in the inductor, switching losses, and capacitor ripple current losses from self-heating.
Therefore, the actual (effective) duty cycle measured may be slightly higher than calculated to compensate for
these power losses. A good approximation for effective duty cycle is :
DC (eff) = (1 - Efficiency x (VIN/VOUT))
(4)
Where the efficiency can be approximated from the curves provided.
8.2.2.9 Inductance Value
The first question we are usually asked is: “How small can I make the inductor?” (because they are the largest
sized component and usually the most costly). The answer is not simple and involves tradeoffs in performance.
Larger inductors mean less inductor ripple current, which typically means less output voltage ripple (for a given
size of output capacitor). Larger inductors also mean more load power can be delivered because the energy
stored during each switching cycle is:
E =L/2 X (lp)2
(5)
Where “lp” is the peak inductor current. An important point to observe is that the LM2733 device will limit its
switch current based on peak current. This means that since lp (maximum) is fixed, increasing L will increase the
maximum amount of power available to the load. Conversely, using too little inductance may limit the amount of
load current which can be drawn from the output.
Best performance is usually obtained when the converter is operated in “continuous” mode at the load current
range of interest, typically giving better load regulation and less output ripple. Continuous operation is defined as
not allowing the inductor current to drop to zero during the cycle. It should be noted that all boost converters shift
over to discontinuous operation as the output load is reduced far enough, but a larger inductor stays “continuous”
over a wider load current range.
To better understand these tradeoffs, a typical application circuit (5V to 12V boost with a 10 µH inductor) will be
analyzed. We will assume:
VIN = 5 V, VOUT = 12 V, VDIODE = 0.5 V, VSW = 0.5 V
Since the frequency is 1.6 MHz (nominal), the period is approximately 0.625 µs. The duty cycle will be 62.5%,
which means the ON time of the switch is 0.390 µs. It should be noted that when the switch is ON, the voltage
across the inductor is approximately 4.5 V.
Using the equation:
V = L (di/dt)
(6)
We can then calculate the di/dt rate of the inductor which is found to be 0.45 A/µs during the ON time. Using
these facts, we can then show what the inductor current will look like during operation:
Figure 25. 10-µH Inductor Current,
5-V – 12-V Boost (LM2733X)
During the 0.390 µs ON time, the inductor current ramps up 0.176 A and ramps down an equal amount during
the OFF time. This is defined as the inductor “ripple current”. It can also be seen that if the load current drops to
about 33 mA, the inductor current will begin touching the zero axis which means it will be in discontinuous mode.
A similar analysis can be performed on any boost converter, to make sure the ripple current is reasonable and
continuous operation will be maintained at the typical load current values.
14
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8.2.2.10 Maximum Switch Current
The maximum FET swtch current available before the current limiter cuts in is dependent on duty cycle of the
application. This is illustrated in the graphs below which show both the typical and specified values of switch
current for both the "X" and "Y" versions as a function of effective (actual) duty cycle:
1600
1600
SWITCH CURRENT LIMIT (mA)
SWITCH CURRENT LIMIT (mA)
1400
VIN = 5V
1200
1000
VIN = 3.3V
800
VIN = 2.7V
600
400
200
0
1400
VIN = 5V
1200
VIN = 3.3V
1000
800
VIN = 2.7V
600
400
200
0
0
20
40
60
80
100
0
20
40
60
80
100
DUTY CYCLE (%) = [1 - EFF*(VIN/VOUT))]
DUTY CYCLE (%) = [1 - EFF*(VIN/VOUT))]
Figure 26. Switch Current Limit vs Duty Cycle - "X"
Figure 27. Switch Current Limit vs Duty Cycle - "Y"
8.2.2.11 Calculating Load Current
As shown in the figure which depicts inductor current, the load current is related to the average inductor current
by the relation:
ILOAD = IIND(AVG) x (1 - DC)
(7)
Where "DC" is the duty cycle of the application. The switch current can be found by:
ISW = IIND(AVG) + ½ (IRIPPLE)
(8)
Inductor ripple current is dependent on inductance, duty cycle, input voltage and frequency:
IRIPPLE = DC x (VIN-VSW) / (f x L)
(9)
combining all terms, we can develop an expression which allows the maximum available load current to be
calculated:
ILOAD(max) = (1 - DC) x (ISW(max) - DC (VIN - VSW))
2fL
(10)
The equation shown to calculate maximum load current takes into account the losses in the inductor or turn-OFF
switching losses of the FET and diode. For actual load current in typical applications, we took bench data for
various input and output voltages for both the "X" and "Y" versions of the LM2733 device and displayed the
maximum load current available for a typical device in graph form:
Figure 28. Max. Load Current vs VIN - "X"
Figure 29. Max. Load Current vs VIN - "Y"
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8.2.2.12 Design Parameters VSW and ISW
The value of the FET "ON" voltage (referred to as VSW in the equations) is dependent on load current. A good
approximation can be obtained by multiplying the "ON Resistance" of the FET times the average inductor
current.
FET on resistance increases at VIN values below 5 V, since the internal N-FET has less gate voltage in this input
voltage range (see Typical Characteristics). Above VIN = 5 V, the FET gate voltage is internally clamped to 5 V.
The maximum peak switch current the device can deliver is dependent on duty cycle. The minimum value is
specified to be > 1 A at duty cycle below 50%. For higher duty cycles, see Typical Characteristics.
8.2.2.13 Thermal Considerations
At higher duty cycles, the increased ON time of the FET means the maximum output current will be determined
by power dissipation within the LM2733 FET switch. The switch power dissipation from ON-state conduction is
calculated by:
P(SW) = DC x IIND(AVE)2 x RDSON
(11)
There will be some switching losses as well, so some derating needs to be applied when calculating IC power
dissipation.
8.2.2.14 Minimum Inductance
In some applications where the maximum load current is relatively small, it may be advantageous to use the
smallest possible inductance value for cost and size savings. The converter will operate in discontinuous mode in
such a case.
The minimum inductance should be selected such that the inductor (switch) current peak on each cycle does not
reach the 1-A current limit maximum. To understand how to do this, an example will be presented.
In the example, the LM2733X will be used (nominal switching frequency 1.6 MHz, minimum switching frequency
1.15 MHz). This means the maximum cycle period is the reciprocal of the minimum frequency:
TON(max) = 1/1.15M = 0.870 µs
(12)
We will assume the input voltage is 5 V, VOUT = 12 V, VSW = 0.2 V, VDIODE = 0.3 V. The duty cycle is:
Duty Cycle = 60.3%
Therefore, the maximum switch ON time is 0.524 µs. An inductor should be selected with enough inductance to
prevent the switch current from reaching 1A in the 0.524 µs ON time interval (see below):
Figure 30. Discontinuous Design, 5V–12V Boost (LM2733X)
The voltage across the inductor during ON time is 4.8V. Minimum inductance value is found by:
V = L X dl/dt, L = V X (dt/dl) = 4.8 (0.524µ/1) = 2.5 µH
(13)
In this case, a 2.7 µH inductor could be used assuming it provided at least that much inductance up to the 1A
current value. This same analysis can be used to find the minimum inductance for any boost application. Using
the slower switching “Y” version requires a higher amount of minimum inductance because of the longer
switching period.
8.2.2.15 Inductor Suppliers
Some of the recommended suppliers of inductors for this product include, but not limited to are Sumida, Coilcraft,
Panasonic, TDK and Murata. When selecting an inductor, make certain that the continuous current rating is high
enough to avoid saturation at peak currents. A suitable core type must be used to minimize core (switching)
losses, and wire power losses must be considered when selecting the current rating.
16
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8.2.3 Application Curves
Figure 31. Efficiency vs. Load Current (5-12V, X-version)
Figure 32. Efficiency vs. Load Current (5-20V X-version)
Figure 33. Efficiency vs. Load Current (5 - 30V Y-version)
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9 Power Supply Recommendations
The device input voltage range is 2.7 V to 14 V.
The voltage on the shutdown pin should not exceed the voltage on the VIN pin. For applications that do not
require a shutdown function the shutdown pin may be connected to the VIN pin. In this case a 47-KΩ resistor is
recommended to be connected between these pins.
10 Layout
10.1 Layout Guidelines
High frequency switching regulators require very careful layout of components in order to get stable operation
and low noise. All components must be as close as possible to the LM2733 device. It is recommended that a 4layer PCB be used so that internal ground planes are available.
Some additional guidelines to be observed:
1. Keep the path between L1, D1, and C2 extremely short. Parasitic trace inductance in series with D1 and C2
will increase noise and ringing.
2. The feedback components R1, R2 and CF must be kept close to the FB pin of U1 to prevent noise injection
on the FB pin trace.
3. If internal ground planes are available (recommended) use vias to connect directly to ground at pin 2 of U1,
as well as the negative sides of capacitors C1 and C2.
10.2 Layout Example
Figure 34. Recommended PCB Component Layout
18
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11 Device and Documentation Support
11.1 Trademarks
All trademarks are the property of their respective owners.
11.2 Electrostatic Discharge Caution
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.
11.3 Glossary
SLYZ022 — TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.
12 Mechanical, Packaging, and Orderable Information
The following pages include mechanical, packaging, and orderable information. This information is the most
current data available for the designated devices. This data is subject to change without notice and revision of
this document. For browser-based versions of this data sheet, refer to the left-hand navigation.
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PACKAGE OPTION ADDENDUM
www.ti.com
30-Sep-2021
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
(4/5)
(6)
LM2733XMF
NRND
SOT-23
DBV
5
1000
Non-RoHS
& Green
Call TI
Level-1-260C-UNLIM
-40 to 125
S52A
LM2733XMF/NOPB
ACTIVE
SOT-23
DBV
5
1000
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 125
S52A
LM2733XMFX/NOPB
ACTIVE
SOT-23
DBV
5
3000
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 125
S52A
LM2733YMF
NRND
SOT-23
DBV
5
1000
Non-RoHS
& Green
Call TI
Level-1-260C-UNLIM
-40 to 125
S52B
LM2733YMF/NOPB
ACTIVE
SOT-23
DBV
5
1000
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 125
S52B
LM2733YMFX/NOPB
ACTIVE
SOT-23
DBV
5
3000
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 125
S52B
(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
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