LT3472 [Linear]
Inverting Micropower DC/DC Converter with Schottky in ThinSOT Package; 反相微功率DC / DC转换器，肖特基采用ThinSOT封装
| 型号： | LT3472 |
| 厂家： | 
Linear |
| 描述： | Inverting Micropower DC/DC Converter with Schottky in ThinSOT Package |
| 文件： | 总8页 (文件大小：151K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LT3483
Inverting Micropower
DC/DC Converter with
Schottky in ThinSOT Package
U
FEATURES
DESCRIPTIO
The LT®3483 is a micropower inverting DC/DC converter
with integrated Schottky and one resistor feedback. The
smallpackagesize, highlevelofintegrationanduseoftiny
surface mount components yield a solution size as small
as 40mm2. The device features a quiescent current of only
40µA at no load, which further reduces to 0.1µA in
shutdown.Acurrentlimited,fixedoff-timecontrolscheme
conserves operating current, resulting in high efficiency
over a broad range of load current. A precisely trimmed
10µA feedback current enables one resistor feedback and
virtually eliminates feedback loading of the output. The
40V switch enables voltage outputs up to –38V to be
generated without the use of costly transformers. The
LT3483’s low 300ns off-time permits the use of tiny low
profile inductors and capacitors to minimize footprint and
cost in space-conscious portable applications.
■
Internal 40V Schottky Diode
■
One Resistor Feedback (Other Resistor Inside)
■
Internal 40V, 200mA Power Switch
■
Generates Regulated Negative Outputs to –38V
■
Low Quiescent Current:
40µA in Active Mode
<1µA in Shutdown Mode
■
Low VCESAT Switch: 200mV at 150mA
■
Wide Input Range: 2.5V to 16V
■
Uses Small Surface Mount Components
■
Output Short-Circuit Protected
■
Available in a 6-Lead SOT-23 Package
U
APPLICATIO S
■
LCD Bias
■
Handheld Computers
■
Battery Backup
The LT3483 is available in the low profile (1mm) SOT-23
(ThinSOTTM) package.
■
Digital Cameras
■
OLED Bias
, LTC and LT are registered trademarks of Linear Technology Corporation.
ThinSOT is a trademark of Linear Technology Corporation.
Patent pending.
U
TYPICAL APPLICATIO
Efficiency and Power Loss
3.6V to –8V DC/DC Converter
75
70
65
60
1000
100
10
V
= 3.6V
IN
0.22µF
10µH
V
IN
3.6V
EFFICIENCY
10Ω
SW
V
OUT
V
IN
D
–8V
25mA
LT3483
SHDN
GND
4.7µF
5pF
806k
POWER
LOSS
FB
2.2µF
1
3483 TA01a
55
0.1
0.1
1
10
100
LOAD CURRENT (mA)
3483 TA01b
3483f
1
LT3483
W W U W
U W
U
ABSOLUTE AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
(Note 1)
VIN Voltage ............................................................. 16V
SW Voltage ............................................................. 40V
D Voltage .............................................................. –40V
FB Voltage ............................................................. 2.5V
SHDN Voltage ......................................................... 16V
Operating Ambient Temperature Range
(Note 2) .................................................. –40°C to 85°C
Junction Temperature.......................................... 125°C
Storage Temperature Range ................ –65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
ORDER PART
NUMBER
TOP VIEW
SW 1
GND 2
FB 3
6 V
LT3483ES6
IN
5 D
4 SHDN
S6 PACKAGE
6-LEAD PLASTIC TSOT-23
S6 PART MARKING
LTBKX
TJMAX = 125°C, θJA = 256°C/W IN FREE AIR
θJA = 120°C/W ON BOARD OVER GROUND PLANE
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C.
VIN = 3.6V, VSHDN = 3.6V unless otherwise specified.
PARAMETER
CONDITIONS
MIN
TYP
MAX
16
UNITS
V
V
V
Operating Range
2.5
IN
IN
Undervoltage Lockout
2
5
2.4
V
FB Comparator Trip Voltage to GND (V
FB Output Current (Note 3)
)
FB Falling
●
●
0
12
mV
µA
mV
µA
µA
%/V
ns
FB
FB = V – 5mV
–10.15
–10
10
–9.75
FB
FB Comparator Hysteresis
FB Rising
Quiescent Current in Shutdown
Quiescent Current (Not Switching)
V
= GND
1
SHDN
FB = –0.05V
2.5V ≤ V ≤ 16V
40
50
I
Line Regulation
0.07
FB
IN
Switch Off-Time
300
200
200
Switch Current Limit
170
230
mA
mV
µA
µA
V
Switch V
I
= 150mA to GND
SW
CESAT
Switch Leakage Current
Rectifier Leakage Current
Rectifier Forward Drop
SHDN Input Low Voltage
SHDN Input High Voltage
SHDN Pin Current
SW = 40V
D = – 40V
1
4
I = 150mA to GND
D
0.64
6
0.4
10
V
1.5
V
µA
Note 1: Absolute Maximum Ratings are those values beyond which the life
Note 3: Current flows out of the pin.
of a device may be impaired.
Note 2: The LTC3483E is guaranteed to meet 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.
3483f
2
LT3483
U W
TYPICAL PERFOR A CE CHARACTERISTICS
VFB Current
VFB Voltage
Switch Off Time
12
9
10.2
10.1
10.0
9.9
400
350
300
250
6
200
150
3
100
50
0
0
9.8
–50
–20
10
40
70
100
–50
–20
10
TEMPERATURE (°C)
70
100
40
–50
–20
10
40
70
100
TEMPERATURE (°C)
TEMPERATURE (°C)
3483 G02
3483 G03
3483 G01
Switch Current Limit
Quiescent Current
SHDN Pin Bias Current
50
40
30
20
10
0
230
220
10
8
T
A
= 25°C
210
200
6
4
190
180
170
2
NOT SWITCHING
V
= –0.05V
FB
0
–50
–20
10
40
70
100
–50
–20
10
40
70
100
4
8
12
0
16
TEMPERATURE (°C)
TEMPERATURE (°C)
SHDN PIN VOLTAGE (V)
3483 G05
3483 G04
3483 G06
U
U
U
PI FU CTIO S
SW: Switch. Connect to external inductor L1 and positive
D: Anode Terminal of Integrated Schottky Diode. Con-
nect to negative terminal of transfer capacitor and exter-
nal inductor L2 (flyback configuration) or to cathode of
external Schottky diode (inverting charge pump
configuration).
terminal of transfer capacitor.
GND: Ground.
FB: Feedback. Place resistor to negative output here. Set
resistor value R1 = VOUT/10µA.
VIN: Input Supply. Must be locally bypassed with 1µF or
greater.
SHDN: Shutdown. Connect to GND to turn device off.
Connect to supply to turn device on.
3483f
3
LT3483
W
BLOCK DIAGRA
L1A
L1B
V
V
IN
OUT
•
•
C
FLY
C
OUT
6
1
5
V
SW
D
IN
1.250V
REFERENCE
300ns
DELAY
125k
+
S
Q
Q
D1
R
Q1
R1
FB
V
OUT
3
25mV
+
–
A3
A2
–
+
–
A1
0.1Ω
0.1Ω
20mV
GND
2
3483 BD
OPTIONAL CHARGE PUMP CONFIGURATION.
L1B REPLACED WITH:
D2
R2
D
V
OUT
U
OPERATIO
The LT3483 uses a constant off-time control scheme to
provide high efficiency over a wide range of output cur-
rents.Operationcanbebestunderstoodbyreferringtothe
Block Diagram. When the voltage at the FB pin is approxi-
mately0V,comparatorA3disablesmostoftheinternalcir-
cuitry.Outputcurrentisthenprovidedbyexternalcapacitor
COUT, which slowly discharges until the voltage at the FB
pin goes above the hysteresis point of A3. Typical hyster-
esis at the FB pin is 10mV. A3 then enables the internal
circuitry, turns on power switch Q1, and the currents in
externalinductorsL1AandL1Bbegintorampup.Oncethe
switch current reaches 200mA, comparator A1 resets the
latch, which turns off Q1 after about 80ns. Inductor cur-
rentflowsthroughtheinternalSchottkyD1toGND,charg-
ing the flying capacitor. Once the 300ns off-time has
elapsed, and internal diode current drops below 250mA
(as detected by comparator A2), Q1 turns on again and
ramps up to 200mA. This switching action continues until
theoutputcapacitorchargeisreplenished(untiltheFBpin
decreases to 0V), then A3 turns off the internal circuitry
andthecyclerepeats.Theinvertingchargepumptopology
replaces L1B with the series combination D2 and R2.
3483f
4
LT3483
W U U
APPLICATIO S I FOR ATIO
U
CHOOSING A REGULATOR TOPOLOGY
Inductor Selection
Several recommended inductors that work well with the
LT3483arelistedinTable1,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
shapes are available. For inverting charge pump regula-
tors with input and output voltages below 7V, a 4.7µH or
6.8µH inductor is usually the best choice. For flyback
regulators or for inverting charge pump regulators where
the input or output voltage is greater than 7V, a 10µH
inductor is usually the best choice. A larger value inductor
can be used to slightly increase the available output
current, but limit it to around twice the value recom-
mended, as too large of an inductance will increase the
output voltage ripple without providing much additional
output current.
Inverting Charge Pump
The inverting charge pump regulator combines an induc-
tor-based step-up with an inverting charge pump. This
configurationusuallyprovidesthebestsize,efficiencyand
output ripple and is applicable where the magnitude of
V
OUT is greater than VIN. Negative outputs to –38V can be
produced with the LT3483 in this configuration. For cases
where the magnitude of VOUT is less than or equal to VIN,
use a 2-inductor or transformer configuration such as the
inverting flyback.
In the inverting charge pump configuration, a resistor is
added in series with the Schottky diode between the
negative output and the D pin of the LT3483. The purpose
ofthisresistoristosmooth/reducethecurrentspikeinthe
flying capacitor when the switch turns on. A 10Ω resistor
works well for a Li+ to –8V application, and the impact to
converter efficiency is less than 3%. The resistor values
recommended in the applications circuits also limit the
switch current during a short-circuit condition at the
output.
Table 1. Recommended Inductors
MAX
DC
H) (mA)
L
I
DCR HEIGHT
PART
(
µ
(
Ω)
(mm) MANUFACTURER
LQH2MCN4R7M02L 4.7 300 0.84
LQH2MCN6R8M02L 6.8 255 1.0
LQH2MCN100M02L 10 225 1.2
0.95 Murata
www.murata.com
SDQ12
10 980 0.72
15 780 1.15
1.2
1.2
Cooper Electronics
Tech
Inverting Flyback
Coupled
Inductor
www.cooperet.com
The inverting flyback regulator, shown in the –5V applica-
tion circuit, uses a coupled inductor and is an excellent
choice where the magnitude of the output is less than or
equal to the supply voltage. The inverting flyback also
performs well in a step-up/invert application, but it occu-
piesmoreboardspacecomparedwiththeinvertingcharge
pump. Also, the maximum |VOUT| using the flyback is less
than can be obtained with the charge pump—it is reduced
from 38V by the magnitudes of VIN and ringing at the
switch node. Under a short-circuit condition at the output,
a proprietary technique limits the switch current and
prevents damage to the LT3483 even with supply voltage
as high as 16V. As an option, a 0.47µF capacitor may be
addedbetweenterminalsDandSWofLT3483tosuppress
ringing at SW.
744876
Coupled
Inductor
10 550 0.46
Würth Elektronik
www.we-online.com
Capacitor Selection
The small size and low ESR of ceramic capacitors make
them ideal for LT3483 applications. Use of X5R and X7R
typesisrecommendedbecausetheyretaintheircapacitance
over wider voltage and temperature ranges than other di-
electrictypes.Alwaysverifythepropervoltagerating.Table
2 shows a list of several ceramic capacitor manufacturers.
Consult the manufacturers for more detailed information
on their entire selection of ceramic capacitors.
A 4.7µF ceramic bypass capacitor on the VIN pin is
recommended where the distance to the power supply or
battery could be more than a couple inches. Otherwise, a
1µF is adequate.
3483f
5
LT3483
W U U
U
APPLICATIO S I FOR ATIO
Conditions that increase inrush current include a larger,
more abrupt voltage step at VIN, a larger flying capacitor,
and an inductor with a low saturation current.
A capacitor in parallel with feedback resistor R1 is recom-
mended to reduce the output voltage ripple. Use a 5pF
capacitor for the inverting charge pump, and a 22pF value
for the inverting flyback or other dual inductor configura-
tions.Outputvoltageripplecanbereducedto20mVinsome
cases using this capacitor in combination with an appro-
priately selected output capacitor.
Whiletheinternaldiodeisdesignedtohandlesuchevents,
the inrush current should not be allowed to exceed 1.5A.
For circuits that use flying capacitors within the recom-
mended range and have input voltages less than 5V,
inrush current remains low, posing no hazard to the
device. In cases where there are large steps at VIN, inrush
currentshouldbemeasuredtoensureoperationwithinthe
limits of the device.
The output capacitor is selected based on desired output
voltageripple.Forlowoutputvoltagerippleintheinverting
flyback configuration, use a 4.7µF to 10µF capacitor. The
invertingchargepumputilizesvaluesrangingfrom0.22µF
to 4.7µF. The following formula is useful to estimate the
output capacitor value needed:
Board Layout Considerations
As with all switching regulators, careful attention must be
given to the PCB board layout and component placement.
Proper layout of the high frequency switching path is
essential. The voltage signals of the SW and D pins have
sharp rising and falling edges. Minimize the length and
area of all traces connected to the SW and D pins. In
particular, it is desirable to minimize the trace length to
and from the flying capacitor, since current in this capaci-
tor switches directions within a cycle. Always use a
ground plane under the switching regulator to minimize
interplane coupling.
2
L •ISW
COUT
=
–VOUT • ∆VOUT
where ISW = 0.25A and ∆VOUT = 30mV. The flying capaci-
tor in the inverting charge pump configuration ranges
from 0.1µF to 0.47µF. Multiply the value predicted by the
above equation for COUT by 1/10 to determine the value
needed for the flying capacitor.
Table 2. Recommended Ceramic Capacitor Manufacturers
MANUFACTURER
AVX
URL
www.avxcorp.com
www.kemet.com
www.murata.com
www.tyuden.com
Suggested Layout (SOT-23)
for Inverting Charge Pump
Kemet
Murata
Taiyo Yuden
GND
C
IN
L1
Setting the Output Voltage
C
FLY
V
IN
The output voltage is programmed using one feedback
resistor according to the following formula:
1
2
3
6
5
4
VOUT
R1= –
10µA
C
OUT
R1
Inrush Current
SHDN
When VIN is increased from ground to operating voltage,
an inrush current will flow through the input inductor and
integrated Schottky diode to charge the flying capacitor.
V
OUT
3483 AI01
3483f
6
LT3483
U
TYPICAL APPLICATIO
3.6V to –8V DC/DC Converter
Low Profile, Small Footprint
Switching Waveform
C2
0.22µF
L1
10µH
D1
V
IN
3.6V
VOUT
20mV/DIV
10Ω
V
OUT
SW
–8V
V
IN
D
25mA
C1
4.7µF
C3
2.2µF
R1
806k
LT3483
SHDN
GND
5pF
ISW
100mA/DIV
FB
2µs/DIV
3483 TA04b
3483 TA04a
C1: MURATA GRM219R61A475KE34B
C2: TAIYO YUDEN LMK107BJ224
C3: MURATA GRM219R61C225KA88B
D1: PHILIPS PMEG2005EB
L1: MURATA LQH2MCN100K02L
U
PACKAGE DESCRIPTIO
S6 Package
6-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1636)
2.90 BSC
(NOTE 4)
0.62
MAX
0.95
REF
1.22 REF
1.4 MIN
1.50 – 1.75
2.80 BSC
3.85 MAX 2.62 REF
(NOTE 4)
PIN ONE ID
RECOMMENDED SOLDER PAD LAYOUT
PER IPC CALCULATOR
0.30 – 0.45
6 PLCS (NOTE 3)
0.95 BSC
0.80 – 0.90
0.20 BSC
DATUM ‘A’
0.01 – 0.10
1.00 MAX
0.30 – 0.50 REF
1.90 BSC
0.09 – 0.20
(NOTE 3)
S6 TSOT-23 0302
NOTE:
1. DIMENSIONS ARE IN MILLIMETERS
2. DRAWING NOT TO SCALE
4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR
5. MOLD FLASH SHALL NOT EXCEED 0.254mm
6. JEDEC PACKAGE REFERENCE IS MO-193
3. DIMENSIONS ARE INCLUSIVE OF PLATING
3483f
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
LT3483
U
TYPICAL APPLICATIO S
3.6V to –22V DC/DC Converter
3.6V to –22V Converter Efficiency and Power Loss
C2
75
70
65
60
55
1000
100
10
L1
0.1µF
D1
10µH
V
IN
EFFICIENCY
3.6V
R
S
30Ω
V
–22V
8mA
OUT
SW
V
D
IN
R1
2.2M
C3
C1
4.7µF
LT3483
SHDN
GND
5pF
1µF
POWER
LOSS
FB
1
C1: TAIYO YUDEN LMK316BJ475MD
C2: TAIYO YUDEN TMK107BJ104 (X5R)
C3: TAIYO YUDEN TMK316BJ105MD
D1: PHILIPS PMEG3002AEB
3483 TA02a
0.1
1
0.1
10
L1: MURATA LQH2MCN100K02L
LOAD CURRENT (mA)
3483 TA02b
–5V DC/DC Converter
–5V Efficiency
75
70
65
60
L1A
L1B
1nF
10µH
10µH
10Ω
V
IN
•
•
SW
V
OUT
V
= 5V
IN
–5V
V
D
IN
C2
C1
4.7µF
LT3483
SHDN
GND
22pF 511k
10µF
FB
V
IN
= 12V
C1: TAIYO YUDEN EMK316BJ475ML
C2: TAIYO YUDEN JMK316BJ106ML
L1A, L1B: WURTH 744876100
3483 TA03a
55
0.1
1
10
100
LOAD CURRENT (mA)
3483 TA03b
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LT1617/LT1617-1 350mA/100mA (I ) High Efficiency
V : 1.2V to 15V, V
ThinSOT Package
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SW
IN
OUT(MAX)
OUT(MAX)
OUT(MAX)
OUT(MAX)
Micropower Inverting DC/DC Converter
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LT1945
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= –34V, I = 5.8mA, I < 1µA
Q SD
SW
IN
ThinSOT Package
Dual Output, Boost/Inverter, 350mA (I ), Constant
Off-Time, High Efficiency Step-Up DC/DC Converter
V : 1.2V to 15V, V
= ±34V, I = 40µA, I < 1µA,
Q SD
SW
IN
MS10 Package
LT3463
Dual Output, Boost/Inverter, 250mA (I ), Constant
V : 2.3V to 15V, V
IN
= ±40V, I = 40µA, I < 1µA
Q SD
SW
Off-Time, High Efficiency Step-Up DC/DC Converter
DFN Package
with Integrated Schottky Diodes
LT3464
LT3472
85mA (I ), High Efficiency Step-Up DC/DC Converter
with Integrated Schottky and PNP Disconnect
V : 2.3V to 10V, V
ThinSOT Package
= 34V, I = 25µA, I < 1µA
Q SD
SW
IN
OUT(MAX)
Boost (350mA) and Inverting (400mA) DC/DC Converter
for CCD Bias with Integrated Schottkys
V : 2.3V to 15V, V
= ±40V, I = 2.8mA, I < 1µA
Q SD
IN
OUT(MAX)
DFN Package
3483f
LT/TP 1004 1K • PRINTED IN THE USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
8
●
●
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
©LINEAR TECHNOLOGY CORPORATION 2004
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