Texas Instruments TPS6104, TPS61040, TPS61041 Series Manual
70
72
74
76
78
80
82
84
86
88
90
0.1 1 10 100
VI= 5 V
VI= 3.6 V
VI= 2.4 V
Efficiency vs Output Current
IO− Output Current − mA
Efficiency − %
V
IN
SW
FB
EN
GND
L1
10mH
D1
R1
R2
C
FF
C
O
1 mF
V
OUT
VINto 28 V
V
IN
1.8 V to 6 V
C
IN
4.7 mF
5
4
2
3
1
VO= 18 V
Copyright © 2016, Texas Instruments Incorporated
Product
Folder
Sample &
Buy
Technical
Documents
Tools &
Software
Support &
Community
TPS61040,TPS61041
SLVS413I –OCTOBER 2002–REVISED DECEMBER 2016
TPS6104x Low-Power DC-DC Boost Converter in SOT-23 and WSON Packages
1 Features
1
• 1.8-V to 6-V Input Voltage Range
• Adjustable Output Voltage Range up to 28 V
• 400-mA (TPS61040) and 250-mA (TPS61041)
Internal Switch Current
• Up to 1-MHz Switching Frequency
• 28-μA Typical No-Load Quiescent Current
• 1-μA Typical Shutdown Current
• Internal Soft Start
• Available in SOT23-5, TSOT23-5,
and 2-mm × 2-mm × 0.8-mm WSON Packages
2 Applications
• LCD Bias Supply
• White-LED Supply for LCD Backlights
• Digital Still Camera
• PDAs, Organizers, and Handheld PCs
• Cellular Phones
• Internet Audio Players
• Standard 3.3-V or 5-V to 12-V Conversion
3 Description
The TPS6104x is a high-frequency boost converter
dedicated for small to medium LCD bias supply and
white LED backlight supplies. The device is ideal to
generate output voltages up to 28 V from a dual-cell
NiMH/NiCd or a single-cell Li-Ion battery. The part
can also be used to generate standard 3.3-V or 5-V
to 12-V power conversions.
The TPS6104x operates with a switching frequency
up to 1 MHz. This frequency allows the use of small
external components using ceramic as well as
tantalum output capacitors. Together with the thin
WSON package, the TPS6104x gives a very small
overall solution size. The TPS61040 device has an
internal 400-mA switch current limit, while the
TPS61041 device has a 250-mA switch current limit,
offering lower output voltage ripple and allows the
use of a smaller form factor inductor for lower power
applications. The low quiescent current (typically 28
μA) together with an optimized control scheme,
allows device operation at very high efficiencies over
the entire load current range.
Device Information
PART NUMBER PACKAGE BODY SIZE (NOM)
SOT-23 (5) 2.90 mm × 1.60 mm
TPS61040
TPS61041
(1) For all available packages, see the orderable addendum at
the end of the datasheet.
SOT (5) 2.90 mm ×1.60 mm
WSON (6) 2.00 mm × 2.00 mm
SOT-23 (5) 2.90 mm ×1.60 mm
WSON (6) 2.00 mm × 2.00 mm
(1)
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.
Typical Application Schematic
TPS61040,TPS61041
SLVS413I –OCTOBER 2002–REVISED DECEMBER 2016
www.ti.com
Table of Contents
1 Features.................................................................. 1
2 Applications ........................................................... 1
3 Description ............................................................. 1
4 Revision History..................................................... 2
5 Pin Configuration and Functions......................... 3
6 Specifications......................................................... 4
6.1 Absolute Maximum Ratings ...................................... 4
6.2 ESD Ratings.............................................................. 4
6.3 Recommended Operating Conditions....................... 4
6.4 Thermal Information.................................................. 4
6.5 Electrical Characteristics........................................... 5
6.6 Typical Characteristics.............................................. 6
7 Detailed Description.............................................. 9
7.1 Overview................................................................... 9
7.2 Functional Block Diagram ......................................... 9
7.3 Feature Description................................................... 9
7.4 Device Functional Modes........................................ 10
8 Application and Implementation ........................ 11
8.1 Application Information............................................ 11
8.2 Typical Application .................................................. 11
8.3 System Examples ................................................... 16
9 Power Supply Recommendations...................... 19
10 Layout................................................................... 19
10.1 Layout Guidelines ................................................. 19
10.2 Layout Example .................................................... 19
11 Device and Documentation Support ................. 20
11.1 Third-Party Products Disclaimer........................... 20
11.2 Related Links ........................................................ 20
11.3 Community Resources.......................................... 20
11.4 Trademarks........................................................... 20
11.5 Electrostatic Discharge Caution............................ 20
11.6 Glossary................................................................ 20
12 Mechanical, Packaging, and Orderable
Information........................................................... 20
4 Revision History
Changes from Revision H (October 2015) to Revision I Page
• Changed CINfrom: 4.7 mF To: 4.7 µF and COFrom: 1 mF To: 1 µF in the Typical Application Schematic.......................... 1
Changes from Revision G (December 2014) to Revision H Page
• Added 500 µs/div label to X-axis of Figure 15. ................................................................................................................... 15
Changes from Revision F (December 2010) to Revision G Page
• Added 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
2
Submit Documentation Feedback Copyright © 2002–2016, Texas Instruments Incorporated
Product Folder Links: TPS61040 TPS61041
GND SW
V
IN
NC
EN FB
3
2
1
4
5
6
3
2
4
5
1
SW
GND
FB
V
IN
EN
www.ti.com
5 Pin Configuration and Functions
TPS61040,TPS61041
SLVS413I –OCTOBER 2002–REVISED DECEMBER 2016
PIN
NAME
EN 4 3 I
FB 3 4 I
GND 2 1 – Ground
NC – 5 – No connection
SW 1 6 I
V
IN
DDC,
DBV NO.
5 2 I Supply voltage pin
DRV NO.
I/O DESCRIPTION
This is the enable pin of the device. Pulling this pin to ground forces the device into shutdown
mode reducing the supply current to less than 1 μA. This pin should not be left floating and needs
to be terminated.
This is the feedback pin of the device. Connect this pin to the external voltage divider to program
the desired output voltage.
Connect the inductor and the Schottky diode to this pin. This is the switch pin and is connected to
the drain of the internal power MOSFET.
DDC Package, DBV Package
5 Pins
Top View
DRV Package
6 Pins
Top View
Pin Functions
Product Folder Links: TPS61040 TPS61041
Submit Documentation FeedbackCopyright © 2002–2016, Texas Instruments Incorporated
3
TPS61040,TPS61041
SLVS413I –OCTOBER 2002–REVISED DECEMBER 2016
www.ti.com
6 Specifications
6.1 Absolute Maximum Ratings
over operating free-air temperature range (unless otherwise noted)
Supply voltages on pin V
Voltages on pins EN, FB
Switch voltage on pin SW
Operating junction temperature, T
Storage temperature, T
(1) Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings
only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended
Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
(2) All voltage values are with respect to network ground terminal.
(2)
IN
(2)
(2)
J
stg
6.2 ESD Ratings
Human body model (HBM), per ANSI/ESDA/JEDEC JS-001
V
(ESD)
(1) JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process. Manufacturing with
(2) JEDEC document JEP157 states that 250-V CDM allows safe manufacturing with a standard ESD control process. Manufacturing with
Electrostatic discharge
Charged-device model (CDM), per JEDEC specification JESD22-
(2)
C101
less than 500-V HBM is possible with the necessary precautions. Pins listed as ±XXX V may actually have higher performance.
less than 250-V CDM is possible with the necessary precautions. Pins listed as ±YYY V may actually have higher performance.
(1)
MIN MAX UNIT
–0.3 7 V
–0.3 VIN+ 0.3 V
30 30 V
–40 150 °C
–65 150 °C
VALUE UNIT
(1)
±2000
±750
V
6.3 Recommended Operating Conditions
MIN NOM MAX UNIT
V
IN
V
OUT
L Inductor
f Switching frequency
C
IN
C
OUT
T
A
T
J
Input voltage range 1.8 6 V
Output voltage range 28 V
(1)
Input capacitor
Output capacitor
(1)
(1)
(1)
2.2 10 μH
1 MHz
4.7 μF
1 μF
Operating ambient temperature –40 85 °C
Operating junction temperature –40 125 °C
(1) See application section for further information.
6.4 Thermal Information
TPS61040 TPS61041
THERMAL METRIC
R
θJA
R
θJC(top)
R
θJB
ψ
JT
ψ
JB
R
θJC(bot)
Junction-to-ambient thermal resistance 205.2 214.7 83.0 205.2 83.0 °C/W
Junction-to-case (top) thermal resistance 118.3 38.5 57.1 118.3 57.1 °C/W
Junction-to-board thermal resistance 34.8 35.4 52.9 34.8 52.9 °C/W
Junction-to-top characterization parameter 12.2 0.4 2.4 12.2 2.4 °C/W
Junction-to-board characterization parameter 33.9 34.8 53.4 33.9 53.4 °C/W
Junction-to-case (bottom) thermal resistance — — 26.9 — 26.9 °C/W
(1) For more information about traditional and new thermal metrics, see the IC Package Thermal Metrics application report, SPRA953.
(1)
5 PINS 5 PINS 6 PINS 5 PINS 6 PINS
UNITDBV DDC DRV DBV DRV
4
Submit Documentation Feedback Copyright © 2002–2016, Texas Instruments Incorporated
Product Folder Links: TPS61040 TPS61041
TPS61040,TPS61041
www.ti.com
SLVS413I –OCTOBER 2002–REVISED DECEMBER 2016
6.5 Electrical Characteristics
VIN= 2.4 V, EN = VIN, TA= –40°C to 85°C, typical values are at TA= 25°C (unless otherwise noted)
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
SUPPLY CURRENT
V
IN
I
Q
I
SD
V
UVLO
ENABLE
V
IH
V
IL
I
I
POWER SWITCH AND CURRENT LIMIT
Vsw Maximum switch voltage 30 V
t
off
t
on
R
DS(on)
R
DS(on)
I
LIM
I
LIM
OUTPUT
V
OUT
V
ref
I
FB
V
FB
(1) The line and load regulation depend on the external component selection. See the application section for further information.
Input voltage range 1.8 6 V
Operating quiescent current I
= 0 mA, not switching, VFB= 1.3 V 28 50 μA
OUT
Shutdown current EN = GND 0.1 1 μA
Undervoltage lockout threshold 1.5 1.7 V
EN high level input voltage 1.3 V
EN low level input voltage 0.4 V
EN input leakage current EN = GND or V
IN
0.1 1 μA
Minimum off time 250 400 550 ns
Maximum on time 4 6 7.5 μs
MOSFET on-resistance VIN= 2.4 V; ISW= 200 mA; TPS61040 600 1000 mΩ
MOSFET on-resistance VIN= 2.4 V; ISW= 200 mA; TPS61041 750 1250 mΩ
MOSFET leakage current VSW= 28 V 1 10 μA
MOSFET current limit TPS61040 350 400 450 mA
MOSFET current limit TPS61041 215 250 285 mA
Adjustable output voltage range V
IN
28 V
Internal voltage reference 1.233 V
Feedback input bias current VFB= 1.3 V 1 μA
Feedback trip point voltage 1.8 V ≤ VIN≤ 6 V 1.208 1.233 1.258 V
Line regulation
Load regulation
(1)
(1)
1.8 V ≤ VIN≤ 6 V; V
CFF= not connected
VIN= 2.4 V; V
OUT
= 18 V; I
OUT
= 18 V; 0 mA ≤ I
= 10 mA;
load
≤ 30 mA 0.15 %/mA
OUT
0.05 %/V
Product Folder Links: TPS61040 TPS61041
Submit Documentation FeedbackCopyright © 2002–2016, Texas Instruments Incorporated
5
70
72
74
76
78
80
82
84
86
88
90
1 2 3 4 5 6
IO = 10 mA
IO = 5 mA
VI − Input Voltage − V
L = 10 µH
VO = 18 V
Efficiency − %
70
72
74
76
78
80
82
84
86
88
90
0.1 1 10
100
L = 10 µH
L = 3.3 µH
IL − Load Current − mA
VO = 18 V
Efficiency − %
Efficiency − %
70
72
74
76
78
80
82
84
86
88
90
0.1 1 10 100
VI = 5 V
VI = 3.6 V
VI = 2.4 V
IO − Output Current − mA
VO = 18 V
70
72
74
76
78
80
82
84
86
88
90
0.1 1 10 100
TPS61040
TPS61041
IL − Load Current − mA
L = 10 µH
VO = 18 V
Efficiency − %
TPS61040,TPS61041
SLVS413I –OCTOBER 2002–REVISED DECEMBER 2016
6.6 Typical Characteristics
η Efficiency
I
Q
V
FB
I
SW
I
CL
R
DS(on)
Quiescent current vs Input voltage and temperature Figure 5
Feedback voltage vs Temperature Figure 6
Switch current limit vs Temperature Figure 7
Switch current limit
R
DS(on)
Line transient response Figure 13
Load transient response Figure 14
Start-up behavior Figure 15
vs Load current
vs Input voltage Figure 4
vs Supply voltage, TPS61041 Figure 8
vs Supply voltage, TPS61040 Figure 9
vs Temperature Figure 10
vs Supply voltage Figure 11
www.ti.com
Table 1. Table of Graphs
FIGURE
Figure 1,
Figure 2,
Figure 3
Figure 1. Efficiency vs Output Current Figure 2. Efficiency vs Load Current
6
Submit Documentation Feedback Copyright © 2002–2016, Texas Instruments Incorporated
Figure 3. Efficiency vs Load Current
Figure 4. Efficiency vs Input Voltage
Product Folder Links: TPS61040 TPS61041
380
385
390
395
400
405
410
415
420
1.8 2.4 3 3.6 4.2 4.8 5.4 6
VCC − Supply Voltage − V
TA = 27°C
I
(CL)
− Current Limit − mA
0
200
400
600
800
1000
1200
−40−30 −20 −10 0 10 20 30 40 50 60 70 80 90
TA − Temperature − °C
TPS61041
TPS61040
r
DS(on)
− Static Drain-Source On-State Resistance − mΩ
230
250
270
290
310
330
350
370
390
410
430
−40−30−20 −10 0 10 20 30 40 50 60 70 80 90
TPS61040
TPS61041
TA − Temperature − °C
I
(SW)
− Switch Current Limit − mA
240
242
244
246
248
250
252
254
256
258
260
1.8 2.4 3 3.6 4.2 4.8 5.4 6
VCC − Supply Voltage − V
TA = 27°C
I
(CL)
− Current Limit − mA
0
5
10
15
20
25
30
35
40
1.8 2.4 3 3.6 4.2 4.8 5.4 6
VI − Input Voltage − V
TA = 85°C
TA = 27°C
TA = −40°C
Quiescent Current − µA
1.23
1.232
1.234
1.236
1.238
1.24
−40 −20 0 20 40 60 80 100 120
VCC = 2.4 V
TA − Temperature − °C
V
FB
− Feedback Voltage − V
www.ti.com
TPS61040,TPS61041
SLVS413I –OCTOBER 2002–REVISED DECEMBER 2016
Figure 5. TPS61040 Quiescent Current vs Input Voltage
Figure 7. TPS6104x Switch Current Limit vs Free-Air
Temperature
Figure 6. Feedback Voltage vs Free-Air Temperature
Figure 8. TPS61041 Current Limit vs Supply Voltage
Figure 9. TPS61040 Current Limit vs Supply Voltage Figure 10. TPS6104x Static Drain-Source On-State
Resistance vs Free-Air Temperature
Product Folder Links: TPS61040 TPS61041
Submit Documentation FeedbackCopyright © 2002–2016, Texas Instruments Incorporated
7
0
100
200
300
400
500
600
700
800
900
1000
1.8 2.4 3 3.6 4.2 4.8 5.4 6
VCC − Supply Voltage − V
TPS61041
TPS61040
r
DS(on)
− Static Drain-Source On-State Resistance − mΩ
TPS61040,TPS61041
SLVS413I –OCTOBER 2002–REVISED DECEMBER 2016
Figure 11. TPS6104x Static Drain-Source On-State Resistance vs Supply Voltage
www.ti.com
8
Submit Documentation Feedback Copyright © 2002–2016, Texas Instruments Incorporated
Product Folder Links: TPS61040 TPS61041
I
peak(typ)ILIM
V
IN
L
100 ns
peak(typ)
400 mA
V
IN
L
100 ns for the TPS61040-Q1
peak(typ)
250 mA
V
IN
L
100 ns for the TPS61041-Q1
=
=
=
+
+
+
×
×
×
+
+
-
RS Latch
Logic
S
R
Gate
Driver
_
Current Limit
Power MOSFET
N-Channel
R
SENSE
Soft
Start
6 s Maxm
On Time
V
REF
= 1.233 V
Error Comparator
400 ns Min
Off Time
Under Voltage
Lockout
Bias Supply
VIN
FB
EN
GND
SW
Copyright © 2016, Texas Instruments Incorporated
TPS61040,TPS61041
www.ti.com
SLVS413I –OCTOBER 2002–REVISED DECEMBER 2016
7 Detailed Description
7.1 Overview
The TPS6104x is a high-frequency boost converter dedicated for small to medium LCD bias supply and white
LED backlight supplies. The device is ideal to generate output voltages up to 28 V from a dual-cell NiMH/NiCd or
a single cell device Li-Ion battery.
7.2 Functional Block Diagram
7.3 Feature Description
7.3.1 Peak Current Control
The internal switch turns on until the inductor current reaches the typical dc current limit (I
(TPS61040) or 250 mA (TPS61041). Due to the internal propagation delay of typical 100 ns, the actual current
exceeds the dc current limit threshold by a small amount. The typical peak current limit can be calculated:
The higher the input voltage and the lower the inductor value, the greater the peak.
By selecting the TPS6104x, it is possible to tailor the design to the specific application current limit requirements.
A lower current limit supports applications requiring lower output power and allows the use of an inductor with a
lower current rating and a smaller form factor. A lower current limit usually has a lower output voltage ripple as
well.
Product Folder Links: TPS61040 TPS61041
) of 400 mA
LIM
(1)
Submit Documentation FeedbackCopyright © 2002–2016, Texas Instruments Incorporated
9
I
LIM
2
I
LIM
4
TPS61040,TPS61041
SLVS413I –OCTOBER 2002–REVISED DECEMBER 2016
www.ti.com
Feature Description (continued)
7.3.2 Soft Start
All inductive step-up converters exhibit high inrush current during start-up if no special precaution is made. This
can cause voltage drops at the input rail during start up and may result in an unwanted or early system shut
down.
The TPS6104x limits this inrush current by increasing the current limit in two steps starting from for 256
cycles to for the next 256 cycles, and then full current limit (see Figure 15).
7.3.3 Enable
Pulling the enable (EN) to ground shuts down the device reducing the shutdown current to 1 μA (typical).
Because there is a conductive path from the input to the output through the inductor and Schottky diode, the
output voltage is equal to the input voltage during shutdown. The enable pin needs to be terminated and should
not be left floating. Using a small external transistor disconnects the input from the output during shutdown as
shown in Figure 17.
7.3.4 Undervoltage Lockout
An undervoltage lockout prevents misoperation of the device at input voltages below typical 1.5 V. When the
input voltage is below the undervoltage threshold, the main switch is turned off.
7.3.5 Thermal Shutdown
An internal thermal shutdown is implemented and turns off the internal MOSFETs when the typical junction
temperature of 168°C is exceeded. The thermal shutdown has a hysteresis of typically 25°C. This data is based
on statistical means and is not tested during the regular mass production of the IC.
7.4 Device Functional Modes
7.4.1 Operation
The TPS6104x operates with an input voltage range of 1.8 V to 6 V and can generate output voltages up to 28
V. The device operates in a pulse-frequency-modulation (PFM) scheme with constant peak current control. This
control scheme maintains high efficiency over the entire load current range, and with a switching frequency up to
1 MHz, the device enables the use of very small external components.
The converter monitors the output voltage, and as soon as the feedback voltage falls below the reference voltage
of typically 1.233 V, the internal switch turns on and the current ramps up. The switch turns off as soon as the
inductor current reaches the internally set peak current of typically 400 mA (TPS61040) or 250 mA (TPS61041).
See Peak Current Control for more information. The second criteria that turns off the switch is the maximum ontime of 6 μs (typical). This is just to limit the maximum on-time of the converter to cover for extreme conditions.
As the switch is turned off the external Schottky diode is forward biased delivering the current to the output. The
switch remains off for a minimum of 400 ns (typical), or until the feedback voltage drops below the reference
voltage again. Using this PFM peak current control scheme the converter operates in discontinuous conduction
mode (DCM) where the switching frequency depends on the output current, which results in very high efficiency
over the entire load current range. This regulation scheme is inherently stable, allowing a wider selection range
for the inductor and output capacitor.
10
Submit Documentation Feedback Copyright © 2002–2016, Texas Instruments Incorporated
Product Folder Links: TPS61040 TPS61041
V
IN
SW
FB
EN
GND
L1
10 μH
D1
R1
2.2 MΩ
R2
160 kΩ
C
FF
22 pF
C2
1 μF
V
OUT
18 V
V
IN
C1
4.7 μF
L1: Sumida CR32-100
D1: Motorola MBR0530
C1: Tayo Yuden JMK212BY475MG
C2: Tayo Yuden TMK316BJ105KL
TPS61040
Copyright © 2016, Texas Instruments Incorporated
TPS61040,TPS61041
www.ti.com
SLVS413I –OCTOBER 2002–REVISED DECEMBER 2016
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 TPS6104x is designed for output voltages up to 28 V with an input voltage range of 1.8 V to 6 V and a
switch peak current limit of 400 mA (250 mA for the TPS61041). The device operates in a pulse-frequencymodulation (PFM) scheme with constant peak current control. This control scheme maintains high efficiency over
the entire load current range, and with a switching frequency up to 1 MHz, the device enables the use of very
small external components. The following section provides a step-by-step design approach for configuring the
TPS61040 as a voltage regulating boost converter for LCD bias power supply, as shown in Figure 12.
8.2 Typical Application
The following section provides a step-by-step design approach for configuring the TPS611040 as a voltage
regulating boost converter for LCD bias supply, as shown in Figure 12.
Figure 12. LCD Bias Supply
8.2.1 Design Requirements
Table 2. Design Parameters
DESIGN PARAMETER EXAMPLE VALUE
Input Voltage 1.8 V to 6 V
Output Voltage 18 V
Output Current 10 mA
8.2.2 Detailed Design Procedure
8.2.2.1 Inductor Selection, Maximum Load Current
Because the PFM peak current control scheme is inherently stable, the inductor value does not affect the stability
of the regulator. The selection of the inductor together with the nominal load current, input and output voltage of
the application determines the switching frequency of the converter. Depending on the application, inductor
values from 2.2 μH to 47 μH are recommended. The maximum inductor value is determined by the maximum on
time of the switch, typically 6 μs. The peak current limit of 400 mA/250 mA (typically) should be reached within
this 6-μs period for proper operation.
Product Folder Links: TPS61040 TPS61041
Submit Documentation FeedbackCopyright © 2002–2016, Texas Instruments Incorporated
11
2
P S( m ax )
lo a d (m a x)
O U T IN
I L f
2 ( V V )
´ ´
= h
´ -
load OUT IN d
S load
2
P
2 I (V V V )
f (I )
I L
´ ´ - +
=
´
IN(min) OUT IN
S(max)
P OUT
V (V V )
f
I L V
´ -
=
´ ´
TPS61040,TPS61041
SLVS413I –OCTOBER 2002–REVISED DECEMBER 2016
www.ti.com
The inductor value determines the maximum switching frequency of the converter. Therefore, select the inductor
value that ensures the maximum switching frequency at the converter maximum load current is not exceeded.
The maximum switching frequency is calculated by the following formula:
where
• IP= Peak current as described in Peak Current Control
• L = Selected inductor value
• V
= The highest switching frequency occurs at the minimum input voltage (2)
IN(min)
If the selected inductor value does not exceed the maximum switching frequency of the converter, the next step
is to calculate the switching frequency at the nominal load current using the following formula:
where
• IP= Peak current as described in Peak Current Control
• L = Selected inductor value
• I
= Nominal load current
load
• Vd = Rectifier diode forward voltage (typically 0.3 V) (3)
A smaller inductor value gives a higher converter switching frequency, but lowers the efficiency.
The inductor value has less effect on the maximum available load current and is only of secondary order. The
best way to calculate the maximum available load current under certain operating conditions is to estimate the
expected converter efficiency at the maximum load current. This number can be taken out of the efficiency
graphs shown in Figure 1 through Figure 4. The maximum load current can then be estimated as follows:
where
• IP= Peak current as described in Peak Current Control
• L = Selected inductor value
• fS
= Maximum switching frequency as calculated previously
max
• η = Expected converter efficiency. Typically 70% to 85% (4)
The maximum load current of the converter is the current at the operation point where the converter starts to
enter the continuous conduction mode. Usually the converter should always operate in discontinuous conduction
mode.
Last, the selected inductor should have a saturation current that meets the maximum peak current of the
converter (as calculated in Peak Current Control). Use the maximum value for I
for this calculation.
LIM
Another important inductor parameter is the dc resistance. The lower the dc resistance, the higher the efficiency
of the converter. See Table 3 and the typical applications for the inductor selection.
Table 3. Recommended Inductor for Typical LCD Bias Supply (see Figure 23)
DEVICE INDUCTOR VALUE COMPONENT SUPPLIER COMMENTS
10 μH Sumida CR32-100 High efficiency
10 μH Sumida CDRH3D16-100 High efficiency
TPS61040
TPS61041 10 μH Murata LQH3C100K24
10 μH Murata LQH4C100K04 High efficiency
4.7 μH Sumida CDRH3D16-4R7 Small solution size
4.7 μH Murata LQH3C4R7M24 Small solution size
High efficiency
Small solution size
12
Submit Documentation Feedback Copyright © 2002–2016, Texas Instruments Incorporated
Product Folder Links: TPS61040 TPS61041
Loading...