LT1944-1EMS [Linear]
Dual Micropower Step-Up DC/DC Converter; 双微升压型DC / DC转换器
| 型号： | LT1944-1EMS |
| 厂家： | 
Linear |
| 描述： | Dual Micropower Step-Up DC/DC Converter |
| 文件： | 总8页 (文件大小：155K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LT1944-1
Dual Micropower Step-Up
DC/DC Converter
U
FEATURES
DESCRIPTIO
The LT®1944-1 is a dual micropower step-up DC/DC
converter in a 10-pin MSOP package. One converter is
designed with a 100mA current limit and a 400ns off-time;
the other with a 175mA current limit and a 1.5µs off-time.
The 1.5µs off-time converter is ideal for generating an
output voltage that is close to the input voltage (i.e. a Li-
Ion to 5V converter, or a two-cell to 3.3V converter). With
aninputvoltagerangeof1.2Vto15V,theLT1944-1isideal
for a wide variety of applications. Both converters feature
a quiescent current of only 20µA at no load, which further
reduces to 0.5µA in shutdown. A current limited, fixed off-
time control scheme conserves operating current, result-
ing in high efficiency over a broad range of load current.
Tiny, low profile inductors and capacitors can be used to
minimize footprint and cost in space-conscious portable
applications.
■
Low Quiescent Current:
20
µ
A in Active Mode
<1µA in Shutdown Mode
■
■
■
■
■
Operates with VIN as Low as 1.2V
Low VCESAT Switches: 85mV at 70mA
Uses Small Surface Mount Components
High Output Voltage: Up to 34V
Tiny 10-Pin MSOP Package
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APPLICATIO S
■
Small TFT LCD Panels
■
Handheld Computers
■
Battery Backup
Digital Cameras
■
, LTC and LT are registered trademarks of Linear Technology Corporation.
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TYPICAL APPLICATIO
Triple Output Power Supply (5V, 15V, –10V) for LCD Displays
L1
5V Output Efficiency
D1
22µH
V
IN
5V
40mA
90
2.7V
TO 4.2V
8
6
85
80
75
70
65
60
55
50
4.7pF
1M
V
SW2
IN
V
= 4.2V
IN
4
2
5
1
SHDN2
FB2
C1
4.7µF
C2
4.7µF
V
= 2.7V
IN
LT1944-1
SHDN1
FB1
324k
GND PGND PGND SW1
10
3
7
9
178k
2M
C3
1µF
0.1
1
10
100
4.7pF
D2
L2
22µH
LOAD CURRENT (mA)
1944-1 TA01a
15V
2.5mA
D3
C1, C2: TAIYO YUDEN JMK212BJ475
C3, C4: TAIYO YUDEN EMK212BJ105
C5: TAIYO YUDEN EMK107BJ104
D1, D2, D3, D4: CENTRAL SEMI CMDSH3
L1, L2: MURATA LQH3C220
C4
5V
1µF
C5
0.1µF
D4
–10V
1mA
1944-1 TA01
1
LT1944-1
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
LT1944-1EMS
IN
PGND
SW2
MS10 PACKAGE
10-LEAD PLASTIC MSOP
MS10 PART
MARKING
TJMAX = 125°C, θJA = 160°C/W
LTTU
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
●
●
1.205
1.23
8
1.255
V
mV
%/V
nA
FB Comparator Hysteresis
FB Voltage Line Regulation
FB Pin Bias Current (Note 3)
Switch Off Time, Switcher 1 (Note 4)
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 Off Time, Switcher 2 (Note 4)
V
V
> 1V
< 0.6V
1.5
1.5
µs
µs
FB
FB
Switch V
I
= 70mA
85
120
125
225
mV
mA
mA
CESAT
SW
Switch Current Limit, Switcher 1
Switch Current Limit, Switcher 2
SHDN Pin Current
65
100
175
130
V
V
= 1.2V
= 5V
2
8
3
12
µA
µA
SHDN
SHDN
SHDN Input Voltage High
SHDN Input Voltage Low
Switch Leakage Current
0.9
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.
temperature range are assured by design, characterization and correlation
with statistical process controls.
Note 2: The LT1944-1E is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the –40°C to 85°C operating
Note 3: Bias current flows into the FB pin.
Note 4: See Figure 1 for Switcher 1 and Switcher 2 locations.
2
LT1944-1
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Switch Saturation Voltage
Feedback Pin Voltage and
Bias Current
(VCESAT
)
Quiescent Current
0.15
0.13
0.10
0.08
0.05
0.03
0
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
I
= 100mA
SWITCH
VOLTAGE
CURRENT
I
= 70mA
SWITCH
V
= 12V
IN
V
= 1.2V
50
IN
–50
0
25
50
75
100
–25
–50
–25
0
25
75
100
–50
–25
0
25
50
75
100
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
1944-1 G01
1944-1 G03
1944-1 G02
Switch Off Time
Switch Current Limit
Shutdown Pin Current
2000
1800
1600
1400
1200
1000
800
25
20
15
10
5
200
175
150
125
100
75
V
= 12V
IN
SWITCHER 2
SWITCHER 2
SWITCHER 1
V
= 1.2V
IN
25°C
V
= 12V
IN
100°C
600
V
= 1.2V
IN
SWITCHER 1
25
400
200
0
0
–50
50
0
5
10
15
–50
0
25
50
75
100
–25
50
75
100
–25
0
SHUTDOWN PIN VOLTAGE (V)
TEMPERATURE (°C)
TEMPERATURE (°C)
1944-1 G03
1944-1 G05
1944-1 G04
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
LT1944-1
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
1.5µs
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
–
12mV
21mV
A2
A2B
SWITCHER 1
SWITCHER 2
GND
PGND PGND
3
9
7
1944-1 BD
Figure 1. LT1944-1 Block Diagram
U
OPERATIO
The LT1944-1 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 100mA, 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 100mA, 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
LT1944-1 contains additional circuitry to provide protec-
tion 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 70mA (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, but with a 175mA current limit and an off-time of
1.5µs. Withthislongeroff-time, switcher2isidealforvery
low duty cycle applications (i.e. Li-Ion to 5V boost
converters).
4
LT1944-1
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W U U
APPLICATIO S I FOR ATIO
Choosing an Inductor
systems with output voltages below 7V, a 10µH inductor
is the best choice, even though the equation above might
specify a smaller value. This is due to the inductor current
overshootthatoccurswhenverysmallinductorvaluesare
used (see Current Limit Overshoot section).
Several recommended inductors that work well with the
LT1944-1 are listed in Table 1, although there are many
other manufacturers and devices that can be used. Con-
sult each manufacturer for more detailed information and
for their entire selection of related parts. Many different
sizes and shapes are available. Use the equations and
recommendations in the next few sections to find the
correct inductance 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 74µH inductor is called for with
the above equation, but a 22µH 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
valuetobeusedforaSEPICregulatorusingtheLT1944-1.
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
VOUT + VD
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
ILIM
Current Limit Overshoot
Inductor Selection—Boost Regulator
Fortheconstantoff-timecontrolschemeoftheLT1944-1,
the power switch is turned off only after the current 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
value to be used for a boost regulator using the LT1944-1
(or at least provides a good starting point). This value
provides a good tradeoff in inductor size and system
performance. 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 = 100mA
(or 175mA) and tOFF = 400ns (or 1.5µs); for designs with
varying VIN such as battery powered applications, use the
minimum VIN value in the above equation. For most
5
LT1944-1
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W U U
APPLICATIO S I FOR ATIO
limited to 100mA (or 175mA), the power switch of the
LT1944-1canhandlelargercurrentswithoutproblem, but
the overall efficiency will suffer. Best results will be ob-
tained when IPEAK is kept below 400mA for the LT1944-1.
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).
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 LT1944-1’s MS10 package. Solid tantalum capaci-
tors(liketheAVXTPS, Sprague593Dfamilies)orOS-CON
capacitors can be used, but they will occupy more board
areathanaceramicandwillhaveahigherESR. Alwaysuse
a capacitor with a sufficient voltage rating.
Diode Selection
For most LT1944-1 applications, the Philips BAT54 or
CentralSemiconductorCMDSH-3surfacemountSchottky
diodes are an ideal choice. Schottky diodes, with their low
forward voltage drop and fast switching speed, are the
best match for the LT1944-1. Many different manufactur-
ers make equivalent parts, but make sure that the compo-
nent is rated to handle at least 100mA.
Ceramic capacitors also make a good choice for the input
decoupling capacitor, which should be placed as close as
possible to the LT1944-1. A 4.7µF input capacitor is
sufficient for most applications. Table 2 shows a list of
severalcapacitormanufacturers. Consultthemanufactur-
ers 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 LT1944-1
provides 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 LT1944-1 (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
LT1944-1
U
TYPICAL APPLICATIO S
Dual Output (5V, 24V) Boost Converter
L1
22µH
D1
V
IN
24V
1mA
2.7V
TO 4.2V
8
10
SW1
4.7pF
1M
V
IN
2
4
1
5
SHDN1
FB1
C1
4.7µF
C2
1µF
LT1944-1
SHDN2
FB2
53.6k
GND PGND PGND SW2
3
7
9
6
324k
C3
4.7pF
D2
1M
4.7µF
L2
22µH
5V
40mA
1944-1 TA02
C1, C3: TAIYO YUDEN JMK212BJ475 (408) 573-4150
C2: TAIYO YUDEN TMK316BJ105
D1, D2: CENTRAL SEMI CMDSH-3
L1, L2: MURATA LQH3C220
(408) 573-4150
(631) 435-1110
(814) 237-1431
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PACKAGE DESCRIPTIO
MS10 Package
10-Lead Plastic MSOP
(Reference LTC DWG # 05-08-1661)
0.034
(0.86)
REF
0.043
(1.10)
MAX
0.118 ± 0.004*
(3.00 ± 0.102)
10 9
8
7 6
0.007
(0.18)
0° – 6° TYP
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)
0.118 ± 0.004**
(3.00 ± 0.102)
0.193 ± 0.006
(4.90 ± 0.15)
0.0197
(0.50)
BSC
* 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
1
2
3
4 5
** DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
MSOP (MS10) 1100
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
LT1944-1
U
TYPICAL APPLICATIO
Four Output Power Supply (±5V, ±15V)
D5
–5V
20mA
C6
0.1µF
C7
4.7µF
D6
L1
22µH
D1
V
IN
5V
20mA
2.7V
TO 4.2V
8
6
4.7pF
1M
V
SW2
IN
4
2
5
1
SHDN2
FB2
C1
4.7µF
C2
4.7µF
LT1944-1
SHDN1
FB1
324k
GND PGND PGND SW1
10
3
7
9
178k
2M
C3
4.7pF
D2
1µF
L2
22µH
15V
2mA
D3
C1, C2, C7: TAIYO YUDEN JMK212BJ475
C3, C4: TAIYO YUDEN EMK212BJ105
C5, C6: TAIYO YUDEN EMK107BJ104
D1, D2, D3, D4, D5, D6: CENTRAL SEMI CMDSH3
L1, L2: MURATA LQH3C220
C5
0.1µF
C4
D4
1µF
–15V
2mA
1944-1 TA03
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DESCRIPTION
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Dual Micropower Step-Up DC/DC Converter
Burst Mode is a trademark of Linear Technology Corporation
19441f LT/TP 0801 2K • PRINTED IN USA
LINEAR TECHNOLOGY CORPORATION 2001
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
8
●
●
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
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LT1945EMS#PBF
LT1945 - Dual Micropower DC/DC Converter with Positive and Negative Outputs; Package: MSOP; Pins: 10; Temperature Range: -40°C to 85°C
Linear
LT1945EMS#TR
LT1945 - Dual Micropower DC/DC Converter with Positive and Negative Outputs; Package: MSOP; Pins: 10; Temperature Range: -40°C to 85°C
Linear
LT1945EMS#TRPBF
LT1945 - Dual Micropower DC/DC Converter with Positive and Negative Outputs; Package: MSOP; Pins: 10; Temperature Range: -40°C to 85°C
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
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