TPS61040-Q1_16 [TI]

Low-Power DC-DC Boost Converter in SOT-23 Package;
TPS61040-Q1_16
型号: TPS61040-Q1_16
厂家: TEXAS INSTRUMENTS    TEXAS INSTRUMENTS
描述:

Low-Power DC-DC Boost Converter in SOT-23 Package

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TPS61040-Q1  
TPS61041-Q1  
www.ti.com  
SGLS276JANUARY 2005  
LOW POWER DC/DC BOOST CONVERTER IN SOT-23 PACKAGE  
FEATURES  
DESCRIPTION  
Qualification in Accordance With AEC-Q100(1)  
The TPS61040/41 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/5 V to 12-V power conversions.  
Qualified For Automotive Application  
Customer-Specifc Configuration Control Can  
Be Supported Along With Major-Change  
Approval  
1.8-V to 6-V Input Voltage Range  
Adjustable Output Voltage Range Up to 28 V  
The TPS61040/41 operates with a switching fre-  
quency up to 1 MHz. This allows the use of small  
external components using ceramic as well as tanta-  
lum output capacitors. Together with the tiny SOT23  
package, the TPS61040/41 gives a small overall  
solution size. The TPS61040 has an internal 400-mA  
switch current limit, while the TPS61041 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  
high efficiencies over the entire load current range.  
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 Softstart  
Available in a Tiny 5-Pin SOT23 Package  
(1)Contact Texas Instruments for details. Q100  
qualification data available on request.  
APPLICATIONS  
DBV PACKAGE  
(TOP VIEW)  
LCD Bias Supply  
White-LED Supply for LCD Backlights  
Digital Still Camera  
PDAs, Organizers, and Handheld PCs  
Cellular Phones  
Internet Audio Player  
1
2
3
5
4
V
IN  
SW  
GND  
FB  
EN  
Standard 3.3 V/5 V to 12 V Conversion  
TYPICAL APPLICATION  
EFFICIENCY  
vs  
OUTPUT CURRENT  
90  
88  
86  
84  
82  
80  
78  
76  
74  
72  
70  
L1  
10 µH  
V
= 18 V  
D1  
O
V = 5 V  
I
V
V
OUT  
V
IN  
to 28 V  
IN  
1.8 V to 6.0 V  
V = 3.6 V  
I
C
FF  
R1  
1
3
2
5
4
V
SW  
IN  
C
1 µF  
O
V = 2.4 V  
I
FB  
C
4.7 µF  
IN  
EN  
GND  
R2  
0.10  
1
10  
100  
I
- Output Current - mA  
O
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas  
Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.  
PRODUCTION DATA information is current as of publication date.  
Copyright © 2005, Texas Instruments Incorporated  
Products conform to specifications per the terms of the Texas  
Instruments standard warranty. Production processing does not  
necessarily include testing of all parameters.  
TPS61040-Q1  
TPS61041-Q1  
www.ti.com  
SGLS276JANUARY 2005  
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.  
(1)  
ORDERING INFORMATION  
TJ  
SWITCH CURRENT LIMIT  
400 mA  
SOT23 PACKAGE  
TPS61040QDBVRQ1  
TPS61041QDBVRQ1  
PACKAGE MARKING  
PHOQ  
-40 to 125°C  
250 mA  
PHPQ  
(1) The DBV package is available in tape & reel. Add R suffix (DBVR) to order quantities of 3000 parts.  
FUNCTIONAL BLOCK DIAGRAM  
SW  
Under Voltage  
Lockout  
Bias Supply  
400 ns Min  
VIN  
FB  
Off Time  
Error Comparator  
-
S
Power MOSFET  
N-Channel  
+
RS Latch  
Logic  
Gate  
Driver  
V
REF  
= 1.233 V  
R
Current Limit  
R
SENSE  
+
_
6 µs Max  
On Time  
EN  
Soft  
Start  
GND  
2
TPS61040-Q1  
TPS61041-Q1  
www.ti.com  
SGLS276JANUARY 2005  
Terminal Functions  
TERMINAL  
I/O  
DESCRIPTION  
NAME NO.  
SW  
1
I
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.  
GND  
FB  
2
3
Ground  
I
I
I
This is the feedback pin of the device. Connect this pin to the external voltage divider to program the desired output  
voltage.  
EN  
4
5
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.  
VIN  
Supply voltage pin  
DETAILED DESCRIPTION  
OPERATION  
The TPS61040/41 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 the Peak Current Control section for more information. The second criteria that turns off the switch is the  
maximum on-time 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 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.  
PEAK CURRENT CONTROL  
The internal switch turns on until the inductor current reaches the typical dc current limit (ILIM) of 400 mA  
(TPS61040) or 250 mA (TPS61042). 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:  
Vin  
L
I
+ I  
)
  100 ns  
peak(typ)  
LIM  
Vin  
L
Vin  
L
I
I
+ 400 mA )  
+ 250 mA )  
  100 ns for the TPS61040  
  100 ns for the TPS61041  
peak(typ)  
peak(typ)  
(1)  
The higher the input voltage and the lower the inductor value, the greater the peak.  
By selecting the TPS61040 or TPS61041, 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.  
SOFTSTART  
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.  
3
TPS61040-Q1  
TPS61041-Q1  
www.ti.com  
SGLS276JANUARY 2005  
DETAILED DESCRIPTION (continued)  
I
LIM  
4
The TPS61040/41 limits this inrush current by increasing the current limit in two steps starting from  
for 256  
I
LIM  
2
cycles to  
for the next 256 cycles, and then full current limit (see Figure 14).  
ENABLE  
Pulling the enable (EN) to ground shuts down the device reducing the shutdown current to 1 µA (typical). Since  
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 18.  
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.  
ABSOLUTE MAXIMUM RATINGS  
over operating free-air temperature (unless otherwise noted)  
(1)  
UNIT  
(2)  
Supply voltages on pin VIN  
-0.3 V to 7 V  
-0.3 V to VIN + 0.3 V  
30 V  
(2)  
Voltages on pins EN, FB  
(2)  
Switch voltage on pin SW  
Continuous power dissipation  
Operating junction temperature  
Storage temperature  
See Dissipation Rating Table  
-40°C to 150°C  
-65°C to 150°C  
260°C  
TJ  
TStg  
Lead temperature (soldering 10 seconds)  
(1) Stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. These are stress ratings  
only, and functional operation of the device at these or any other conditions beyond those indicated under recommended operating  
conditions is not implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.  
(2) All voltage values are with respect to network ground terminal.  
DISSIPATION RATING TABLE(1)  
T
A 25°C  
DERATING FACTOR  
ABOVE TA = 25°C  
TA = 70°C  
POWER RATING  
TA = 85°C  
POWER RATING  
PACKAGE  
POWER RATING  
DBV  
357 mW  
3.5 mW/°C  
192 mW  
140 mW  
(1) The thermal resistance junction to ambient of the 5-pin SOT23 is 250°C/W.  
RECOMMENDED OPERATING CONDITIONS  
MIN  
TYP  
MAX UNIT  
Vin  
VOUT  
L
Input voltage range  
1.8  
6
V
V
Output voltage range  
Inductor(1)  
Switching frequency(1)  
28  
2.2  
10  
µH  
MHz  
µF  
µF  
°C  
f
1
(1)  
Cin  
COUT  
TJ  
Input capacitor  
4.7  
(1)  
Output capacitor  
1
Operating junction temperature  
-40  
125  
(1) See the Application Section for further information.  
4
TPS61040-Q1  
TPS61041-Q1  
www.ti.com  
SGLS276JANUARY 2005  
ELECTRICAL CHARACTERISTICS  
VIN = 2.4 V, EN = VIN, TJ = -40°C to 125°C, typical values are at TA = 25°C (unless otherwise noted)  
PARAMETER  
SUPPLY CURRENT  
TEST CONDITIONS  
MIN  
TYP  
MAX UNIT  
VIN  
Input voltage range  
1.8  
6
50  
1
V
µA  
µA  
V
IQ  
Operating quiescent current  
Shutdown current  
IOUT = 0 mA, not switching, VFB = 1.3 V  
EN = GND  
28  
0.1  
1.5  
ISD  
VUVLO  
ENABLE  
VIH  
Under-voltage lockout threshold  
1.7  
EN high level input voltage  
EN low level input voltage  
EN input leakage current  
1.3  
V
V
VIL  
0.4  
1
II  
EN = GND or VIN  
0.1  
µA  
POWER SWITCH AND CURRENT LIMIT  
Vsw  
Maximum switch voltage  
Minimum off time  
30  
550  
7.5  
V
toff  
250  
4
400  
6
ns  
ton  
Maximum on time  
µs  
RDS(ON)  
RDS(ON)  
MOSFET on-resistance  
MOSFET on-resistance  
MOSFET leakage current  
MOSFET current limit  
MOSFET current limit  
VIN = 2.4 V; Isw = 200 mA; TPS61040  
VIN = 2.4 V; Isw = 200 mA; TPS61041  
Vsw = 28 V  
600  
750  
1
1100  
1300  
10  
mΩ  
mΩ  
µA  
mA  
mA  
ILIM  
TPS61040  
325  
200  
400  
250  
500  
325  
ILIM  
TPS61041  
OUTPUT  
VOUT  
Vref  
Adjustable output voltage range(1)  
Internal voltage reference  
VIN  
28  
V
V
1.233  
IFB  
Feedback input bias current  
Feedback trip point voltage  
VFB = 1.3 V  
1
µA  
V
VFB  
1.8 V VIN 6 V  
1.2 1.233  
0.05  
1.27  
1.8 VVIN 6 V; VOUT = 18 V; Iload = 10 mA; Cff  
= not connected  
(2)  
Line regulation  
%/V  
Load regulation(2)  
VIN = 2.4 V; VOUT = 18 V; 0 mA IOUT 30 mA  
0.15  
%/mA  
(1) Cannot be production tested. Assured by design.  
(2) The line and load regulation depend on the external component selection. See the Application Section for further information.  
5
TPS61040-Q1  
TPS61041-Q1  
www.ti.com  
SGLS276JANUARY 2005  
TYPICAL CHARACTERISTICS  
Table of Graphs  
FIGURE  
vs Load current  
1, 2, 3  
4
η
Efficiency  
vs Input voltage  
IQ  
Quiescent current  
Feedback voltage  
Switch current limit  
vs Input voltage and temperature  
vs Temperature  
5
VFB  
ISW  
6
vs Temperature  
7
vs Supply voltage, TPS61041  
vs Supply voltage, TPS61040  
vs Temperature  
8
ICL  
Switch current limit  
RDSon  
9
10  
11  
12  
13  
14  
RDSon  
vs Supply voltage  
Line transient response  
Load transient response  
Start-up behavior  
EFFICIENCY  
EFFICIENCY  
vs  
LOAD CURRENT  
vs  
OUTPUT CURRENT  
90  
88  
86  
84  
82  
80  
78  
76  
74  
72  
70  
90  
88  
86  
84  
82  
80  
78  
76  
74  
72  
70  
V
O
= 18 V  
L = 10 µH  
= 18 V  
V
O
V = 5 V  
I
TPS61040  
V = 3.6 V  
I
TPS61041  
V = 2.4 V  
I
0.10  
1
10  
100  
0.10  
1
10  
100  
I
O
- Output Current - mA  
I
L
- Load Current - mA  
Figure 1.  
Figure 2.  
6
 
TPS61040-Q1  
TPS61041-Q1  
www.ti.com  
SGLS276JANUARY 2005  
EFFICIENCY  
vs  
LOAD CURRENT  
EFFICIENCY  
vs  
INPUT VOLTAGE  
90  
V
90  
88  
86  
84  
82  
80  
78  
76  
74  
= 18 V  
L = 10 µH  
= 18 V  
O
88  
V
O
I
O
= 10 mA  
86  
84  
L = 10 µH  
I
O
= 5 mA  
L = 3.3 µH  
82  
80  
78  
76  
74  
72  
70  
72  
70  
1
2
3
4
5
6
0.10  
1
10  
100  
I - Load Current - mA  
L
V - Input Voltage - V  
I
Figure 3.  
Figure 4.  
TPS61040  
QUIESCENT CURRENT  
vs  
FEEDBACK VOLTAGE  
vs  
FREE-AIR TEMPERATIRE  
INPUT VOLTAGE  
40  
1.24  
T = 85°C  
A
35  
30  
25  
20  
15  
10  
1.238  
T = 27°C  
A
1.236  
1.234  
T = -40°C  
A
V
CC  
= 2.4 V  
1.232  
1.23  
5
0
1.8  
2.4  
3
3.6  
4.2  
4.8  
5.4  
6
-40 -20  
0
20  
40  
60  
80 100 120  
T - Temperature - °C  
A
V - Input Voltage - V  
I
Figure 5.  
Figure 6.  
7
 
TPS61040-Q1  
TPS61041-Q1  
www.ti.com  
SGLS276JANUARY 2005  
TPS61040/41  
SWITCH CURRENT LIMIT  
vs  
TPS61041  
CURRENT LIMIT  
vs  
FREE-AIR TEMPERATURE  
SUPPLY VOLTAGE  
260  
258  
256  
254  
252  
430  
410  
390  
370  
TPS61040  
T
A
= 27°C  
350  
330  
310  
290  
270  
250  
248  
246  
244  
TPS61041  
250  
230  
242  
240  
1.8  
2.4  
3
3.6  
4.2  
4.8  
5.4  
6
-40 -30 -20 -10  
0
10 20 30 40 50 60 70 80 90  
T
A
- Temperature - °C  
V
CC  
- Supply Voltage - V  
Figure 7.  
Figure 8.  
TPS61040  
TPS61040/41  
CURRENT LIMIT  
vs  
STATIC DRAIN-SOURCE ON-STATE RESISTANCE  
vs  
SUPPLY VOLTAGE  
FREE-AIR TEMPERATURE  
420  
1200  
415  
410  
405  
400  
395  
390  
1000  
800  
600  
400  
TPS61041  
T
A
= 27°C  
TPS61040  
200  
0
385  
380  
−4030 −20 −10 0 10 20 30 40 50 60 70 80 90  
1.8  
2.4  
3
3.6  
4.2  
4.8  
5.4  
6
T
A
− Temperature − °C  
V
CC  
- Supply Voltage - V  
Figure 9.  
Figure 10.  
8
TPS61040-Q1  
TPS61041-Q1  
www.ti.com  
SGLS276JANUARY 2005  
TPS61040/41  
STATIC DRAIN-SOURCE ON-STATE RESISTANCE  
vs  
SUPPLY VOLTAGE  
1000  
V
O
= 18 V  
900  
800  
700  
600  
500  
400  
300  
200  
V
I
2.4 V to 3.4 V  
TPS61041  
TPS61040  
V
O
100 mV/div  
100  
0
200 µS/div  
1.8  
2.4  
3
3.6  
4.2  
4.8  
5.4  
6
V
CC  
− Supply Voltage − V  
Figure 11.  
Figure 12. Line Transient Response  
V
O
= 18 V  
V
O
= 18 V  
V
O
V
O
100 mA/div  
5 V/div  
EN  
1 V/div  
V
O
1 mA to 10 mA  
I
I
50 mA/div  
200 µS/div  
Figure 13. Load Transient Rresponse  
Figure 14. Start-Up Behavior  
9
TPS61040-Q1  
TPS61041-Q1  
www.ti.com  
SGLS276JANUARY 2005  
APPLICATION INFORMATION  
INDUCTOR SELECTION, MAXIMUM LOAD CURRENT  
Since 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  
between 2.2 µH up 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.  
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:  
Vin  
(Vout–Vin)  
min  
fS  
+
max  
I
  L   Vout  
P
(2)  
Where:  
IP = Peak current as described in the previous peak current control section  
L = Selected inductor value  
Vinmin = The highest switching frequency occurs at the minimum input voltage  
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:  
2   I  
  (Vout–Vin ) Vd)  
load  
fSǒIloadǓ+  
2
I
  L  
P
(3)  
Where:  
IP = Peak current as described in the previous peak current control section  
L = Selected inductor value  
Iload = Nominal load current  
Vd = Rectifier diode forward voltage (typically 0.3 V)  
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, Figure 2, Figure 3, and Figure 4. The maximum load current can then be estimated as  
follows:  
2
P
I
L
fS  
max  
I
+ h  
load max  
Where:  
2   (Vout * Vin)  
(4)  
IP = Peak current as described in the previous peak current control section  
L = Selected inductor value  
fSmax = Maximum switching frequency as calculated previously  
η = Expected converter efficiency. Typically 70% to 85%.  
10  
TPS61040-Q1  
TPS61041-Q1  
www.ti.com  
SGLS276JANUARY 2005  
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 the peak current control section). Use the maximum value for ILIM for this calculation.  
Another important inductor parameter is the dc resistance. The lower the dc resistance, the higher the efficiency  
of the converter. See the Table 1 and the Typical Applications section for the inductor selection.  
Table 1. Recommended Inductor for Typical LCD Bias Supply (see Figure 15)  
DEVICE  
INDUCTOR VALUE  
10 µH  
COMPONENT SUPPLIER  
Sumida CR32-100  
COMMENTS  
High efficiency  
10 µH  
Sumida CDRH3D16-100  
Murata LQH4C100K04  
Sumida CDRH3D16-4R7  
Murata LQH3C4R7M24  
High efficiency  
TPS61040  
10 µH  
High efficiency  
4.7 µH  
Small solution size  
Small solution size  
4.7 µH  
High efficiency  
Small solution size  
TPS61041  
10 µH  
Murata LQH3C100K24  
SETTING THE OUTPUT VOLTAGE  
The output voltage is calculated as:  
R1  
R2  
+ 1.233 V   ǒ1 ) Ǔ  
V
out  
(5)  
For battery powered applications, a high impedance voltage divider should be used with a typical value for R2 of  
200 kand a maximum value for R1 of 2.2 M. Smaller values might be used to reduce the noise sensitivity of  
the feedback pin.  
A feed-forward capacitor across the upper feedback resistor R1 is required to provide sufficient overdrive for the  
error comparator. Without a feed-forward capacitor, or one whose value is too small, the TPS61040/41 shows  
double pulses or a pulse burst instead of single pulses at the switch node (SW), causing higher output voltage  
ripple. If this higher output voltage ripple is acceptable, the feed-forward capacitor can be left out.  
The lower the switching frequency of the converter, the larger the feed-forward capacitor value required. A good  
starting point is to use a 10-pF feed-forward capacitor. As a first estimation, the required value for the  
feed-forward capacitor at the operation point can also be calculated using the following formula:  
1
C
+
FF  
fS  
20  
2   p   
  R1  
(6)  
Where:  
R1 = Upper resistor of voltage divider  
fS = Switching frequency of the converter at the nominal load current (see the previous section for  
calculating the switching frequency)  
CFF = Choose a value that comes closest to the result of the calculation  
11  
TPS61040-Q1  
TPS61041-Q1  
www.ti.com  
SGLS276JANUARY 2005  
The larger the feed-forward capacitor the worse the line regulation of the device. Therefore, when concern for  
line regulation is paramount, the selected feed-forward capacitor should be as small as possible. See the next  
section for more information about line and load regulation.  
LINE AND LOAD REGULATION  
The line regulation of the TPS61040/41 depends on the voltage ripple on the feedback pin. Usually a 50-mV  
peak-to-peak voltage ripple on the feedback pin FB gives good results.  
Some applications require a very tight line regulation and can only allow a small change in output voltage over a  
certain input voltage range. If no feed-feedforwardforward capacitor CFF is used across the upper resistor of the  
voltage feedback divider, the device has the best line regulation. Without the feed-forward capacitor the output  
voltage ripple is higher because the TPS61040/41 shows output voltage bursts instead of single pulses on the  
switch pin (SW), increasing the output voltage ripple. Increasing the output capacitor value reduces the output  
voltage ripple.  
If a larger output capacitor value is not an option, a feed-forward capacitor CFF can be used as described in the  
previous section. The use of a feed-forward capacitor increases the amount of voltage ripple present on the  
feedback pin (FB). The greater the voltage ripple on the feedback pin (50 mV), the worse the line regulation.  
There are two ways to improve the line regulation further:  
1. Use a smaller inductor value to increase the switching frequency which will lower the output voltage ripple,  
as well as the voltage ripple on the feedback pin.  
2. Add a small capacitor from the feedback pin (FB) to ground to reduce the voltage ripple on the feedback pin  
down to 50 mV again. As a starting point, the same capacitor value as selected for the feed-forward  
capacitor CFF can be used.  
OUTPUT CAPACITOR SELECTION  
For best output voltage filtering, a low ESR output capacitor is recommended. Ceramic capacitors have a low  
ESR value but tantalum capacitors can be used as well, depending on the application.  
Assuming the converter does not show double pulses or pulse bursts on the switch node (SW), the output  
voltage ripple can be calculated as:  
I
  L  
I
out  
1
P
DV  
+
 
) I   ESR  
ǒ
Ǔ
out  
P
C
fS(Iout) Vout ) Vd–Vin  
out  
(7)  
Where:  
IP = Peak current as described in the previous Peak Current Control section  
L = Selected inductor value  
Iout = Nominal load current  
fS (Iout) = Switching frequency at the nominal load current as calculated previously  
Vd = Rectifier diode forward voltage (typically 0.3 V)  
Cout = Selected output capacitor  
ESR = Output capacitor ESR value  
Refer to Table 2 and typical applications section for choosing the output capacitor.  
Table 2. Recommended Input and Output Capacitors  
DEVICE  
CAPACITOR  
4.7 µF/X5R/0805  
10 µF/X5R/0805  
1.0 µF/X7R/1206  
1.0 µF/X5R/1206  
4.7 µF/X5R/1210  
VOLTAGE RATING  
COMPONENT SUPPLIER  
Tayo Yuden JMK212BY475MG  
Tayo Yuden JMK212BJ106MG  
Tayo Yuden TMK316BJ105KL  
Tayo Yuden GMK316BJ105KL  
Tayo Yuden TMK325BJ475MG  
COMMENTS  
CIN/COUT  
CIN/COUT  
COUT  
6.3 V  
6.3 V  
25 V  
35 V  
25 V  
TPS61040/41  
COUT  
COUT  
12  
TPS61040-Q1  
TPS61041-Q1  
www.ti.com  
SGLS276JANUARY 2005  
INPUT CAPACITOR SELECTION  
For good input voltage filtering, low ESR ceramic capacitors are recommended. A 4.7-µF ceramic input capacitor  
is sufficient for most of the applications. For better input voltage filtering this value can be increased. See Table 2  
and the Typical Applications section for input capacitor recommendations.  
DIODE SELECTION  
To achieve high efficiency a Schottky diode should be used. The current rating of the diode should meet the  
peak current rating of the converter as it is calculated in the section peak current control. Use the maximum  
value for ILIM for this calculation. See Table 3 and the Typical Applications section for the selection of the  
Schottky diode.  
Table 3. Recommended Schottky Diode for Typical LCD Bias Supply (see Figure 15)  
DEVICE  
REVERSE VOLTAGE  
COMPONENT SUPPLIER  
ON Semiconductor MBR0530  
ON Semiconductor MBR0520  
ON Semiconductor MBRM120L  
Toshiba CRS02  
COMMENTS  
30 V  
20 V  
20 V  
30 V  
TPS61040/41  
High efficiency  
LAYOUT CONSIDERATIONS  
Typical for all switching power supplies, the layout is an important step in the design; especially at high peak  
currents and switching frequencies. If the layout is not carefully done, the regulator might show noise problems  
and duty cycle jitter.  
The input capacitor should be placed as close as possible to the input pin for good input voltage filtering. The  
inductor and diode should be placed as close as possible to the switch pin to minimize the noise coupling into  
other circuits. Since the feedback pin and network is a high impedance circuit the feedback network should be  
routed away from the inductor. The feedback pin and feedback network should be shielded with a ground plane  
or trace to minimize noise coupling into this circuit.  
Wide traces should be used for connections in bold as shown in Figure 15. A star ground connection or ground  
plane minimizes ground shifts and noise.  
D1  
L1  
V
O
C
FF  
R1  
V
V
IN  
SW  
FB  
IN  
C
O
C
IN  
R2  
EN  
GND  
Figure 15. Layout Diagram  
13  
 
TPS61040-Q1  
TPS61041-Q1  
www.ti.com  
SGLS276JANUARY 2005  
L1  
10 µH  
D1  
V
18 V  
OUT  
V
IN  
1.8 V to 6 V  
TPS61040  
C
22 pF  
FF  
R1  
2.2 MW  
V
IN  
SW  
FB  
C2  
1 µF  
C1  
4.7 µF  
L1:  
D1:  
C1:  
C2:  
Sumida CR32-100  
Motorola MBR0530  
Tayo Yuden JMK212BY475MG  
Tayo Yuden TMK316BJ105KL  
EN  
GND  
R2  
160 kW  
Figure 16. LCD Bias Supply  
L1  
10 µH  
D1  
V
O
18 V  
TPS61040  
C
FF  
R1  
2.2 MW  
22 pF  
V
V
IN  
SW  
FB  
IN  
C2  
1 µF  
1.8 V to 6 V  
C1  
4.7 µF  
DAC or Analog Voltage  
0 V = 25 V  
1.233 V = 18 V  
EN  
GND  
R2  
160 kW  
L1:  
Sumida CR32-100  
D1:  
C1:  
C2:  
Motorola MBR0530  
Tayo Yuden JMK212BY475MG  
Tayo Yuden GMK316BJ105KL  
Figure 17. LCD Bias Supply With Adjustable Output Voltage  
R3  
200 kW  
BC857C  
L1  
10 µH  
D1  
V
IN  
V
OUT  
1.8 V to 6 V  
18 V / 10 mA  
TPS61040  
R1  
C
FF  
2.2 MW  
22 pF  
V
IN  
SW  
FB  
C2  
1 µF  
C3  
0.1 µF  
(Optional)  
C1  
4.7 µF  
R2  
160 kW  
EN  
GND  
L1:  
D1:  
C1:  
C2:  
Sumida CR32-100  
Motorola MBR0530  
Tayo Yuden JMK212BY475MG  
Tayo Yuden TMK316BJ105KL  
Figure 18. LCD Bias Supply With Load Disconnect  
14  
TPS61040-Q1  
TPS61041-Q1  
www.ti.com  
SGLS276JANUARY 2005  
D3  
V2 = -10 V/15 mA  
D2  
C4  
4.7 µF  
C3  
1 µF  
L1  
D1  
6.8 µH  
V1 = 10 V/15 mA  
TPS61040  
C
FF  
22 pF  
R1  
1.5 MW  
V
SW  
FB  
IN  
V
IN  
= 2.7 V to 5 V  
C2  
1 µF  
C1  
4.7 µF  
L1:  
Murata LQH4C6R8M04  
D1, D2, D3: Motorola MBR0530  
EN  
GND  
R2  
C1:  
Tayo Yuden JMK212BY475MG  
210 kW  
C2, C3, C4: Tayo Yuden EMK316BJ105KF  
Figure 19. Positive and Negative Output LCD Bias Supply  
L1  
6.8 µH  
D1  
V
O =  
12 V/35 mA  
TPS61040  
C
4.7 pF  
FF  
R1  
1.8 MW  
V
IN  
3.3 V  
V
IN  
SW  
FB  
C2  
4.7 µF  
C1  
10 µF  
L1:  
Murata LQH4C6R8M04  
Motorola MBR0530  
Tayo Yuden JMK212BJ106MG  
Tayo Yuden EMK316BJ475ML  
EN  
GND  
R2  
205 kW  
D1:  
C1:  
C2:  
Figure 20. Standard 3.3-V to 12-V Supply  
D1  
3.3 µH  
TPS61040  
5 V/45 mA  
C
FF  
3.3 pF  
R1  
620 kW  
V
1.8 V to 4 V  
SW  
FB  
IN  
C2  
4.7 µF  
C1  
4.7 µF  
R2  
200 kW  
EN  
GND  
L1:  
D1:  
Murata LQH4C3R3M04  
Motorola MBR0530  
C1, C2: Tayo Yuden JMK212BY475MG  
Figure 21. Dual Battery Cell to 5 V/50-mA Conversion  
Efficiency Aprox. Equals 84% at VIN = 2.4 V to VO = 5 V/45 mA  
15  
TPS61040-Q1  
TPS61041-Q1  
www.ti.com  
SGLS276JANUARY 2005  
L1  
D1  
10 µH  
D2  
24 V  
V
CC  
= 2.7 V to 6 V  
V
IN  
SW  
(Optional)  
C1  
4.7 µF  
FB  
L1:  
D1:  
C1:  
C2:  
Murata LQH4C100K04  
Motorola MBR0530  
Tayo Yuden JMK212BY475MG  
Tayo Yuden TMK316BJ105KL  
C2  
1 µF  
R
82 Ω  
EN  
PWM  
100 Hz to 500 Hz  
GND  
S
Figure 22. White LED Supply With Adjustable Brightness Control  
Using a PWM Signal on the Enable Pin Efficiency Aprox. Equals 86% at VIN = 3 V, ILED = 15 mA  
D1  
L1  
MBRM120L  
10 µH  
C2  
D2  
24 V  
(Optional)  
V
CC  
= 2.7 V to 6 V  
100 nF  
V
SW  
FB  
IN  
C1  
4.7 µF  
R1  
120 kW  
EN  
GND  
R
S
110 W  
L1:  
D1:  
C1:  
C2:  
Murata LQH4C3R3M04  
Motorola MBR0530  
Tayo Yuden JMK212BY475MG  
Standard Ceramic Capacitor  
Analog Brightness Control  
3.3 V Led Off  
R2 160 kW  
0 V Iled = 20 mA  
A. A smaller output capacitor value for C2 causes a larger LED ripple.  
Figure 23. White LED Supply With Adjustable Brightness Control  
Using an Analog Signal on the Feedback Pin  
16  
IMPORTANT NOTICE  
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enhancements, improvements, and other changes to its products and services at any time and to discontinue  
any product or service without notice. Customers should obtain the latest relevant information before placing  
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accordance with TI’s standard warranty. Testing and other quality control techniques are used to the extent TI  
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