LT1944EMS [Linear]
Dual Micropower Step-Up DC/DC Converter; 双微升压型DC / DC转换器
| 型号： | LT1944EMS |
| 厂家： | 
Linear |
| 描述： | Dual Micropower Step-Up DC/DC Converter |
| 文件： | 总8页 (文件大小：164K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LT1944
Dual Micropower Step-Up
DC/DC Converter
U
FEATURES
DESCRIPTIO
The LT®1944 is a dual micropower step-up DC/DC con-
verter in a 10-pin MSOP package. Each converter is
designed with a 350mA current limit and an input voltage
range of 1.2V to 15V, making the LT1944 ideal for a wide
variety of applications. Both converters feature a quies-
centcurrentofonly20µAatnoload,whichfurtherreduces
to 0.5µA in shutdown. A current limited, fixed off-time
control scheme conserves operating current, resulting in
highefficiencyoverabroadrangeofloadcurrent. The36V
switch allows high voltage outputs up to 34V to be easily
generated in a simple boost topology without the use of
costly transformers. The LT1944’s low off-time of 400ns
permits the use of tiny, low profile inductors and capaci-
tors to minimize footprint and cost in space-conscious
portable applications.
■
Low Quiescent Current:
20
<1
µ
A in Active Mode
µA in Shutdown Mode
■
■
■
■
■
Operates with VIN as Low as 1.2V
Low VCESAT Switch: 250mV at 300mA
Uses Small Surface Mount Components
High Output Voltage: Up to 34V
Tiny 10-Pin MSOP Package
U
APPLICATIO S
■
LCD Bias
■
Handheld Computers
■
Battery Backup
Digital Cameras
■
, LTC and LT are registered trademarks of Linear Technology Corporation.
U
TYPICAL APPLICATIO
Dual Output (5V, 30V) Boost Converter
5V Output Efficiency
90
L1
4.7µH
D1
V
IN
5V
80mA
85
2.7V
V
= 4.2V
IN
TO 4.2V
8
10
SW1
80
75
70
65
60
55
50
4.7pF
1M
V
IN
V
= 2.7V
IN
2
4
1
5
SHDN1
FB1
C1
4.7µF
C2
10µF
LT1944
SHDN2
FB2
324k
GND PGND PGND SW2
3
7
9
6
86.6k
0.1
1
10
100
LOAD CURRENT (mA)
C3
4.7pF
D2
2M
1944 TA01a
1µF
L2
10µH
30V
8mA
1944 TA01
C1: TAIYO YUDEN JMK212BJ475
C2: TAIYO YUDEN JMK316BJ106
C3: TAIYO YUDEN GMK316BJ105
D1, D2: ON SEMI MBR0540
L1: MURATA LQH3C4R7
L2: MURATA LQH3C100
1
LT1944
W W U W
U
W
U
ABSOLUTE AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
(Note 1)
ORDER PART
NUMBER
TOP VIEW
VIN, SHDN1, SHDN2 Voltage ................................... 15V
SW1, SW2 Voltage .................................................. 36V
FB1, FB2 Voltage .......................................................VIN
Current into FB1, FB2 Pins ..................................... 1mA
Junction Temperature........................................... 125°C
Operating Temperature Range (Note 2) .. –40°C to 85°C
Storage Temperature Range ................. –65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
FB1
SHDN1
GND
SHDN2
FB2
1
2
3
4
5
10 SW1
9
8
7
6
PGND
V
LT1944EMS
IN
PGND
SW2
MS10 PACKAGE
10-LEAD PLASTIC MSOP
MS10 PART
MARKING
TJMAX = 125°C, θJA = 160°C/W
LTTR
Consult LTC Marketing for parts specified with wider operating temperature ranges.
The ● denotes the specifications which apply over the full operating
ELECTRICAL CHARACTERISTICS
temperature range, otherwise specifications are at TA = 25°C. VIN = 1.2V, VSHDN = 1.2V unless otherwise noted.
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Minimum Input Voltage
Quiescent Current, Each Switcher
1.2
V
Not Switching
20
30
1
µA
µA
V
= 0V
SHDN
FB Comparator Trip Point
FB Comparator Hysteresis
FB Voltage Line Regulation
FB Pin Bias Current (Note 3)
Switch Off Time
●
●
1.205
1.23
8
1.255
V
mV
%/V
nA
1.2V < V < 12V
0.05
30
0.1
80
IN
V
= 1.23V
FB
V
V
> 1V
< 0.6V
400
1.5
ns
µs
FB
FB
Switch V
I
= 300mA
250
350
350
400
mV
mA
CESAT
SW
Switch Current Limit
SHDN Pin Current
250
0.9
V
V
= 1.2V
= 5V
2
8
3
12
µA
µA
SHDN
SHDN
SHDN Input Voltage High
SHDN Input Voltage Low
Switch Leakage Current
V
V
0.25
5
Switch Off, V = 5V
0.01
µA
SW
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: The LT1944 is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.
Note 3: Bias current flows into the FB pin.
2
LT1944
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Switch Saturation Voltage
(VCESAT
Feedback Pin Voltage and
Bias Current
)
Quiescent Current
0.60
0.55
0.50
0.45
0.40
0.35
0.30
0.25
0.20
0.15
0.10
1.25
1.24
1.23
1.22
1.21
1.20
50
40
30
20
10
0
25
23
21
19
17
15
V
= 1.23V
FB
NOT SWITCHING
VOLTAGE
CURRENT
I
I
= 500mA
= 300mA
SWITCH
V
IN
= 12V
SWITCH
V
IN
= 1.2V
–50
–25
0
25
50
75
100
–50
–25
0
25
50
75
100
–50
–25
0
25
50
75
100
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
1944 G03
1944 G01
1944 G02
Switch Off Time
Switch Current Limit
Shutdown Pin Current
550
500
450
400
350
300
250
400
350
300
250
200
150
100
50
25
20
15
10
5
V
IN
= 12V
V
= 1.2V
IN
V
IN
= 1.2V
25°C
V
IN
= 12V
100°C
0
0
–50
–25
0
25
50
75
100
–50
–25
0
25
50
75
100
0
5
10
15
TEMPERATURE (°C)
TEMPERATURE (°C)
SHUTDOWN PIN VOLTAGE (V)
1944 G04
1944 G05
1944 G03
U
U
U
PI FU CTIO S
FB1 (Pin 1): Feedback Pin for Switcher 1. Set the output
SW2 (Pin 6): Switch Pin for Switcher 2. This is the
collector of the internal NPN power switch. Minimize the
metal trace area connected to the pin to minimize EMI.
voltage by selecting values for R1 and R2.
SHDN1 (Pin 2): Shutdown Pin for Switcher 1. Tie this pin
to 0.9V or higher to enable device. Tie below 0.25V to turn
it off.
PGND (Pins 7, 9): Power Ground. Tie these pins directly
to the local ground plane. Both pins must be tied.
GND (Pin 3): Ground. Tie this pin directly to the local
ground plane.
VIN (Pin 8): Input Supply Pin. Bypass this pin with a
capacitor as close to the device as possible.
SHDN2 (Pin 4): Shutdown Pin for Switcher 2. Tie this pin
to 0.9V or higher to enable device. Tie below 0.25V to turn
it off.
SW1 (Pin 10): Switch Pin for Switcher 1. This is the
collector of the internal NPN power switch. Minimize the
metal trace area connected to the pin to minimize EMI.
FB2 (Pin 5): Feedback Pin for Switcher 2. Set the output
voltage by selecting values for R1B and R2B.
3
LT1944
W
BLOCK DIAGRA
D1
D2
L1
L2
V
IN
V
V
V
IN
OUT1
OUT2
C3
C1
C2
V
IN
SHDN1
SW1
SW2
SHDN2
8
2
10
6
4
V
IN
R5
40k
R6
40k
R6B
40k
R5B
40k
A1
A1B
+
+
ENABLE
ENABLE
V
V
OUT1
OUT2
R1B
–
–
R1
Q1B
(EXTERNAL)
(EXTERNAL)
FB1
FB2
Q1
400ns
400ns
Q2
Q2B
X10
1
5
Q3
Q3B
ONE-SHOT
ONE-SHOT
X10
R2
R2B
(EXTERNAL)
DRIVER
DRIVER
(EXTERNAL)
R3
30k
R3B
30k
RESET
RESET
+
+
–
R4
140k
R4B
140k
0.12Ω
0.12Ω
–
42mV
42mV
A2
A2B
GND
PGND PGND
3
9
7
1944 BD
Figure 1. LT1944 Block Diagram
U
OPERATIO
The LT1944 uses a constant off-time control scheme to
provide high efficiencies over a wide range of output
current. Operation can be best understood by referring to
theblockdiagraminFigure1.Q1andQ2alongwithR3and
R4 form a bandgap reference used to regulate the output
voltage. When the voltage at the FB1 pin is slightly above
1.23V, comparator A1 disables most of the internal cir-
cuitry. Output current is then provided by capacitor C2,
which slowly discharges until the voltage at the FB1 pin
drops below the lower hysteresis point of A1 (typical
hysteresis at the FB pin is 8mV). A1 then enables the
internal circuitry, turns on power switch Q3, and the
current in inductor L1 begins ramping up. Once the switch
current reaches 350mA, comparator A2 resets the one-
shot, which turns off Q3 for 400ns. L1 then delivers
current to the output through diode D1 as the inductor
current ramps down. Q3 turns on again and the inductor
current ramps back up to 350mA, then A2 resets the one-
shot, again allowing L1 to deliver current to the output.
This switching action continues until the output voltage is
charged up (until the FB1 pin reaches 1.23V), then A1
turns off the internal circuitry and the cycle repeats. The
LT1944 contains additional circuitry to provide protection
during start-up and under short-circuit conditions. When
the FB1 pin voltage is less than approximately 600mV, the
switch off-time is increased to 1.5µs and the current limit
is reduced to around 250mA (70% of its normal value).
This reduces the average inductor current and helps
minimize the power dissipation in the power switch and in
the external inductor and diode. The second switching
regulator operates in the same manner.
4
LT1944
U
W U U
APPLICATIO S I FOR ATIO
Choosing an Inductor
voltages below 7V, a 4.7µH inductor is the best choice,
even though the equation above might specify a smaller
value. This is due to the inductor current overshoot that
occurs when very small inductor values are used (see
Current Limit Overshoot section).
Several recommended inductors that work well with the
LT1944arelistedinTable1,althoughtherearemanyother
manufacturers and devices that can be used. Consult each
manufacturer for more detailed information and for their
entire selection of related parts. Many different sizes and
shapesareavailable. Usetheequationsandrecommenda-
tionsinthenextfewsectionstofindthecorrectinductance
value for your design.
For higher output voltages, the formula above will give
large inductance values. For a 2V to 20V converter (typical
LCD Bias application), a 21µH inductor is called for with
the above equation, but a 10µH inductor could be used
without excessive reduction in maximum output current.
Table 1. Recommended Inductors
PART
VALUE (
µH)
MAX DCR (
Ω)
VENDOR
Inductor Selection—SEPIC Regulator
LQH3C4R7
LQH3C100
LQH3C220
4.7
10
22
0.26
0.30
0.92
Murata
(714) 852-2001
www.murata.com
The formula below calculates the approximate inductor
value to be used for a SEPIC regulator using the LT1944.
As for the boost inductor selection, a larger or smaller
value can be used.
CD43-4R7
CD43-100
CDRH4D18-4R7
CDRH4D18-100
4.7
10
4.7
10
0.11
0.18
0.16
0.20
Sumida
(847) 956-0666
www.sumida.com
V
OUT + VD
ILIM
DO1608-472
DO1608-103
DO1608-223
4.7
10
22
0.09
0.16
0.37
Coilcraft
(847) 639-6400
www.coilcraft.com
L = 2
tOFF
Current Limit Overshoot
Inductor Selection—Boost Regulator
For the constant off-time control scheme of the LT1944,
thepowerswitchisturnedoffonlyafterthe350mAcurrent
limit is reached. There is a 100ns delay between the time
when the current limit is reached and when the switch
actually turns off. During this delay, the inductor current
exceeds the current limit by a small amount. The peak
inductor current can be calculated by:
The formula below calculates the appropriate inductor
valuetobeusedforaboostregulatorusingtheLT1944(or
at least provides a good starting point). This value pro-
vides a good tradeoff in inductor size and system perfor-
mance. Pick a standard inductor close to this value. A
larger value can be used to slightly increase the available
output current, but limit it to around twice the value
calculated below, as too large of an inductance will in-
crease the output voltage ripple without providing much
additional output current. A smaller value can be used
(especially for systems with output voltages greater than
12V) to give a smaller physical size. Inductance can be
calculated as:
V
IN(MAX) − VSAT
IPEAK =ILIM
+
100ns
L
Where VSAT = 0.25V (switch saturation voltage). The
current overshoot will be most evident for systems with
high input voltages and for systems where smaller induc-
tor values are used. This overshoot can be beneficial as it
helps increase the amount of available output current for
smaller inductor values. This will be the peak current seen
by the inductor (and the diode) during normal operation.
For designs using small inductance values (especially at
input voltages greater than 5V), the current limit over-
shoot can be quite high. Although it is internally current
V
OUT − V
) + VD
IN MIN
(
L =
tOFF
ILIM
where VD = 0.4V (Schottky diode voltage), ILIM = 350mA
and tOFF = 400ns; for designs with varying VIN such as
battery powered applications, use the minimum VIN value
in the above equation. For most systems with output
5
LT1944
U
W U U
APPLICATIO S I FOR ATIO
limited to 350mA, the power switch of the LT1944 can
handle larger currents without problem, but the overall
efficiency will suffer. Best results will be obtained when
Setting the Output Voltage
Set the output voltage for each switching regulator by
choosing the appropriate values for feedback resistors R1
and R2 (see Figure 1).
IPEAK is kept below 700mA for the LT1944.
Capacitor Selection
VOUT
1.23V
R1= R2
−1
LowESR(EquivalentSeriesResistance)capacitorsshould
beusedattheoutputtominimizetheoutputripplevoltage.
Multilayer ceramic capacitors are the best choice, as they
have a very low ESR and are available in very small
packages. Their small size makes them a good companion
to the LT1944’s MS10 package. Solid tantalum capacitors
(like the AVX TPS, Sprague 593D families) or OS-CON
capacitors can be used, but they will occupy more board
areathanaceramicandwillhaveahigherESR. Alwaysuse
a capacitor with a sufficient voltage rating.
Diode Selection
For most LT1944 applications, the Motorola MBR0520
surface mount Schottky diode (0.5A, 20V) is an ideal
choice. Schottky diodes, with their low forward voltage
drop and fast switching speed, are the best match for the
LT1944. For higher output voltage applications the 30V
MBR0530 or 40V MBR0540 can be used. Many different
manufacturers make equivalent parts, but make sure that
the component is rated to handle at least 0.35A.
Ceramic capacitors also make a good choice for the input
decoupling capacitor, which should be placed as close as
possible to the LT1944. A 4.7µF input capacitor is suffi-
cient for most applications. Table 2 shows a list of several
capacitor manufacturers. Consult the manufacturers for
more detailed information and for their entire selection of
related parts.
Lowering Output Voltage Ripple
Using low ESR capacitors will help minimize the output
ripple voltage, but proper selection of the inductor and the
output capacitor also plays a big role. The LT1944 pro-
vides energy to the load in bursts by ramping up the
inductor current, then delivering that current to the load.
If too large of an inductor value or too small of a capacitor
value is used, the output ripple voltage will increase
because the capacitor will be slightly overcharged each
burst cycle. To reduce the output ripple, increase the
outputcapacitorvalueoradda4.7pFfeed-forwardcapaci-
tor in the feedback network of the LT1944 (see the circuits
in the Typical Applications section). Adding this small,
inexpensive 4.7pF capacitor will greatly reduce the output
voltage ripple.
Table 2. Recommended Capacitors
CAPACITOR TYPE
VENDOR
Ceramic
Taiyo Yuden
(408) 573-4150
www.t-yuden.com
Ceramic
Ceramic
AVX
(803) 448-9411
www.avxcorp.com
Murata
(714) 852-2001
www.murata.com
6
LT1944
U
TYPICAL APPLICATIO S
2-Cell Dual Output (3.3V, 5V) Boost Converter
L1
4.7µH
D1
V
IN
5V
40mA
1.8V
TO 3V
8
10
SW1
4.7pF
1M
V
IN
2
4
1
5
SHDN1
FB1
C1
4.7µF
C2
10µF
LT1944
SHDN2
FB2
324k
GND PGND PGND SW2
3
7
9
6
604k
C3
C1: TAIYO YUDEN JMK212BJ475
(408) 573-4150
4.7pF
D2
1M
10µF
C2, C3: TAIYO YUDEN JMK316BJ106 (408) 573-4150
L2
4.7µH
D1, D2: ON SEMI MBR0520
L1, L2: MURATA LQH3C4R7
(800) 282-9855
(814) 237-1431
3.3V
80mA
1944 TA02
2-Cell to 5V Efficiency
2-Cell to 3.3V Efficiency
90
85
80
75
70
65
60
55
50
90
85
80
75
70
65
60
55
50
V
= 3V
IN
V
V
= 3V
IN
= 1.8V
IN
V
= 1.8V
IN
0.1
1
10
100
0.1
1
10
100
LOAD CURRENT (mA)
LOAD CURRENT (mA)
1944 TA02a
1944 TA02b
U
PACKAGE DESCRIPTIO
MS10 Package
10-Lead Plastic MSOP
(LTC DWG # 05-08-1661)
0.118 ± 0.004*
(3.00 ± 0.102)
0.034
(0.86)
REF
0.043
(1.10)
MAX
10 9 8
7 6
0.007
(0.18)
0° – 6° TYP
0.118 ± 0.004**
(3.00 ± 0.102)
0.193 ± 0.006
(4.90 ± 0.15)
SEATING
PLANE
0.007 – 0.011
(0.17 – 0.27)
0.021 ± 0.006
(0.53 ± 0.015)
0.005 ± 0.002
(0.13 ± 0.05)
0.0197
(0.50)
BSC
MSOP (MS10) 1100
1
2
3
4 5
* DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH,
PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
** DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tationthattheinterconnectionofitscircuitsasdescribedhereinwillnotinfringeonexistingpatentrights.
7
LT1944
U
TYPICAL APPLICATIO
Four Output Power Supply for Color LCD Displays
Q1
C7
0.1µF
–6.5V
500µA
C6
2.2µF
D3A
D3B
Q2
140k
D2B
D2A
20V
C3
0.1µF
500µA
C5
1µF
C4
0.1µF
L1
10µH
D1
V
IN
10V
5mA
2.7V
TO 4.2V
8
10
SW1
1M
V
IN
2
4
1
5
SHDN1
FB1
C1
4.7µF
C2
2.2µF
LT1944
SHDN2
FB2
140k
GND PGND PGND SW2
3
7
9
6
C8
1µF
82.5Ω
L2
10µH
D4
15mA
5 WHITE LEDs
1944 TA03
C1: TAIYO YUDEN JMK212BJ475
(408) 573-4150
(408) 573-4150
C2, C6: TAIYO YUDEN LMK212BJ225
C3, C4, C7: TAIYO YUDEN EMK107BJ104 (408) 573-4150
C5, C8: TAIYO YUDEN TMK316BJ105
D1, D4: ON SEMI MBR0530
D2, D3: ZETEX BAT54S
L1, L2: SUMIDA CLQ4D10-100
Q1, Q2: ON SEMI MMBT3906
(408) 573-4150
(800) 282-9855
(631) 543-7100
(847) 956-0666
(800) 282-9855
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Burst Mode is a registered trademark of Linear Technology Corporation
1944f LT/TP 1001 2K • PRINTED IN USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
8
●
●
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
LINEAR TECHNOLOGY CORPORATION 2001
相关型号：
LT1944EMS#PBF
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Linear
LT1945IMS#PBF
LT1945 - Dual Micropower DC/DC Converter with Positive and Negative Outputs; Package: MSOP; Pins: 10; Temperature Range: -40°C to 85°C
Linear
LT1945IMS#TR
IC 0.4 A DUAL SWITCHING CONTROLLER, PDSO8, PLASTIC, MSOP-10, Switching Regulator or Controller
Linear
LT1945IMS#TRPBF
LT1945 - Dual Micropower DC/DC Converter with Positive and Negative Outputs; Package: MSOP; Pins: 10; Temperature Range: -40°C to 85°C
Linear
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