LT1617-1 [Linear]
Micropower Inverting DC/DC Converters in SOT-23; 微功率输出DC / DC采用SOT -23转换器
| 型号： | LT1617-1 |
| 厂家： | 
Linear |
| 描述： | Micropower Inverting DC/DC Converters in SOT-23 |
| 文件： | 总8页 (文件大小：146K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LT1617/LT1617-1
Micropower Inverting
DC/DC Converters
in SOT-23
U
FEATURES
DESCRIPTIO
The LT®1617/LT1617-1 are micropower inverting DC/DC
converters in a 5-lead SOT-23 package. The LT1617 is
designed for higher power systems with a 350mA current
limit and an input voltage range of 1.2V to 15V, whereas
the LT1617-1 is intended for lower power and single-cell
applications with a 100mA current limit and an extended
input voltage range of 1V to 15V. Otherwise, the two
devices are functionally equivalent. Both devices 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.
The 36V switch allows high voltage outputs up to –34V to
beeasilygeneratedwithouttheuseofcostlytransformers.
The LT1617’s low off-time of 400ns permits the use of
tiny, low profile inductors and capacitors to minimize
footprint and cost in space-conscious portable applications.
, LTC and LT are registered trademarks of Linear Technology Corporation.
■
Low Quiescent Current:
20
µ
A in Active Mode
<1µA in Shutdown Mode
■
■
■
■
■
Operates with VIN as Low as 1V
Low VCESAT Switch: 250mV at 300mA
Uses Small Surface Mount Components
High Output Voltage: Up to –34V
Tiny 5-Lead SOT-23 Package
U
APPLICATIO S
■
LCD Bias
■
Handheld Computers
■
Battery Backup
Digital Cameras
■
U
TYPICAL APPLICATION
1-Cell Li-Ion to –15V Inverting Converter
Efficiency
80
C3
L1
L2
0.22µF
22µH
22µH
V
–15V
IN
2.5V TO 4.2V
V
= 4.2V
V
75
70
65
60
55
50
IN
12mA
5
1
V
SW
IN
= 2.5V
D1
267k
IN
C2
4.7µF
LT1617
4
3
SHDN
NFB
GND
2
C1
4.7µF
24.9k
C1: TAIYO YUDEN LMK316BJ475
C2: TAIYO YUDEN EMK316BJ475
C3: TAIYO YUDEN TMK316BJ224
L1, L2: MURATA LQH3C220K34
D1: MOTOROLA MBR0530
1617/-1 TA01
0.1
1
10
30
LOAD CURRENT (mA)
1617/-1 TA01a
1
LT1617/LT1617-1
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, SHDN Voltage................................................... 15V
SW Voltage .............................................................. 36V
NFB Voltage ............................................................. –3V
Current into NFB Pin ............................................. –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
SW 1
GND 2
NFB 3
5 V
IN
LT1617ES5
LT1617ES5-1
4 SHDN
S5 PACKAGE
5-LEAD PLASTIC SOT-23
S5 PART MARKING
TJMAX = 125°C, θJA = 256°C/W
LTKF
LTKA
Consult factory for Industrial and Military grade parts.
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
LT1617-1
LT1617
1.0
1.2
V
V
Quiescent Current
Not Switching
20
30
1
µA
µA
V
= 0V
SHDN
FB Comparator Trip Point
FB Comparator Hysteresis
Output Voltage Line Regulation
FB Pin Bias Current (Note 3)
Switch Off Time
●
●
–1.205
1.3
–1.23
8
–1.255
V
mV
%/V
µA
1.2V < V < 12V
0.05
2
0.1
2.7
IN
V
= –1.23V
NFB
400
ns
Switch V
I
I
= 60mA (LT1617-1)
= 300mA (LT1617)
85
250
120
350
mV
mV
CESAT
SW
SW
Switch Current Limit
SHDN Pin Current
LT1617-1
LT1617
75
300
100
350
125
400
mA
mA
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.
Note 2: The LT1617 and LT1617-1 are 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.
Note 3: Bias current flows out of the NFB pin.
2
LT1617/LT1617-1
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
5
4
3
2
1
0
25
V
= 1.23V
FB
NOT SWITCHING
23
21
19
17
15
VOLTAGE
CURRENT
I
I
= 500mA
= 300mA
SWITCH
V
= 12V
IN
SWITCH
V
= 1.2V
50
IN
–50
–25
0
25
75
100
–50
–25
0
25
50
75
100
–50
–25
0
25
50
75
100
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
1617/-1 G03
1617/-1 G01
1617/-1 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
= 12V
IN
V
= 1.2V
IN
LT1617
V
= 1.2V
IN
25°C
V
= 12V
IN
100°C
LT1617-1
–25
V
= 12V
IN
V
= 1.2V
50
IN
0
0
–50
–25
0
25
50
75
100
–50
0
25
75
100
0
5
10
15
TEMPERATURE (°C)
TEMPERATURE (°C)
SHUTDOWN PIN VOLTAGE (V)
1617/-1 G04
1617/-1 G05
1617/-1 G06
U
U
U
PI FU CTIO S
SW (Pin 1): Switch Pin. This is the collector of the internal
NPN power switch. Minimize the metal trace area con-
nected to this pin to minimize EMI.
VOUT − 1.23
R1=
1.23
R2
+ 2 •10−6
GND (Pin 2): Ground. Tie this pin directly to the local
ground plane.
SHDN (Pin 4): Shutdown Pin. Tie this pin to 0.9V or higher
toenablethedevice. Tiebelow0.25Vtoturnoffthedevice.
NFB (Pin 3): Feedback Pin. Set the output voltage by
selecting values for R1 and R2 (see Figure 1):
VIN (Pin 5): Input Supply Pin. Bypass this pin with a
capacitor as close to the device as possible.
3
LT1617/LT1617-1
W
BLOCK DIAGRA
C3
L1
L2
V
V
OUT
IN
D1
C1
C2
V
IN
SHDN
SW
5
4
1
R5
80k
R6
80k
A1
+
ENABLE
400ns
–
Q1
Q2
X10
Q3
ONE-SHOT
DRIVER
R3
60k
RESET
V
OUT
+
R4
280k
R1
0.12Ω
(EXTERNAL)
NFB
3
–
42mV*
A2
R2
GND
(EXTERNAL)
2
1617/-1 BD
* 12mV FOR LT1617-1
Figure 1. LT1617 Block Diagram
U
OPERATIO
The LT1617 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 NFB pin is slightly below
–1.23V, comparator A1 disables most of the internal
circuitry. Output current is then provided by capacitor C2,
which slowly discharges until the voltage at the NFB pin
goes above the hysteresis point of A1 (typical hysteresis
at the NFB pin is 8mV). A1 then enables the internal
circuitry, turns on power switch Q3, and the current in
inductors L1 and L2 begins ramping up. Once the switch
current reaches 350mA, comparator A2 resets the one-
shot, which turns off Q3 for 400ns. L2 continues to deliver
current to the output while Q3 is off. Q3 turns on again and
the inductor currents ramp back up until the switch
current reaches 350mA, then A2 again resets the one-
shot. This switching action continues until the output
voltage is charged up (until the NFB pin reaches –1.23V),
then A1 turns off the internal circuitry and the cycle
repeats. The LT1617-1 operates in the same manner,
except the switch current is limited to 100mA (the A2
reference voltage is 12mV instead of 42mV).
4
LT1617/LT1617-1
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W U U
APPLICATIO S I FOR ATIO
Choosing an Inductor
For higher output voltages, the formula above will give
large inductance values. For a 2V to 20V converter (typical
LCD bias application), a 47µH inductor is called for with
the above equation, but a 10µH or 22µH inductor could be
used without excessive reduction in maximum output
current.
Several recommended inductors that work well with the
LT1617 and LT1617-1 are listed in Table 1, although there
are many other manufacturers and devices that can be
used. Consult each manufacturer for more detailed infor-
mation 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.
Inductor Selection—Inverting Charge Pump Regulator
For the inverting regulator, the voltage seen by the internal
power switch is equal to the sum of the absolute value of
the input and output voltages, so that generating high
output voltages from a high input voltage source will often
exceed the 36V maximum switch rating. For instance, a
12V to–30V converter using the inverting topology would
generate 42V on the SW pin, exceeding its maximum
rating. For such a system, an inverting charge pump is the
best topology.
Table 1. Recommended Inductors
PART
VALUE (µH)
MAX DCR (
Ω
)
VENDOR
LQH3C4R7
LQH3C100
LQH3C220
4.7
10
22
0.26
0.30
0.92
Murata
(714) 852-2001
www.murata.com
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
The formula below calculates the approximate inductor
value to be used for an inverting charge pump regulator
using the LT1617. As for the boost inductor selection, a
larger or smaller value can be used. For designs with
varying VIN such as battery powered applications, use the
minimum VIN value in the equation below.
DO1608-472
DO1608-103
D01608-223
4.7
10
22
0.09
0.16
Coilcraft
(847) 639-6400
www.coilcraft.com
Inductor Selection—Inverting Regulator
The formula below calculates the appropriate inductor
value to be used for an inverting regulator using the
LT1617 or LT1617-1 (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 (both inductors should be the same 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:
VOUT − V
) + VD
IN MIN
(
L =
tOFF
ILIM
Current Limit Overshoot
For the constant off-time control scheme of the LT1617,
the power switch is turned off only after the 350mA (or
100mA) 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:
VOUT + VD
V
IN(MAX) − VSAT
IPEAK =ILIM
+
100ns
L = 2
tOFF
L
ILIM
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-
whereVD =0.4V(Schottkydiodevoltage), ILIM=350mAor
100mA, and tOFF = 400ns.
5
LT1617/LT1617-1
U
W U U
APPLICATIO S I FOR ATIO
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
limited to 350mA, the power switch of the LT1617 can
handle larger currents without problem, but the overall
efficiency will suffer. Best results will be obtained when
IPEAK is kept below 700mA for the LT1617 and below
400mA for the LT1617-1.
Diode Selection
For most LT1617 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
LT1617. For higher output voltage applications the 30V
MBR0530 can be used. Many different manufacturers
make equivalent parts, but make sure that the component
is rated to handle at least 0.5A. For LT1617-1 applications,
a Phillips BAT54 or a Central Semiconductor CMDSH-3
works well.
Lowering Output Voltage Ripple
Capacitor Selection
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 LT1617 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
output capacitor value or add a 100pF feed-forward ca-
pacitor in the feedback network of the LT1617 (see the
circuits in the Typical Applications section). Adding this
small, inexpensive 100pF capacitor will greatly reduce the
output voltage ripple.
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 LT1617’s SOT-23 package. Solid tantalum capaci-
tors(liketheAVXTPS, Sprague593Dfamilies)orOS-CON
capacitors can be used, but they will occupy more board
area than a ceramic and will have a larger ESR. Always use
a capacitor with a sufficient voltage rating.
Ceramic capacitors also make a good choice for the input
decoupling capacitor, which should be placed as close as
possible to the LT1617. 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.
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
LT1617/LT1617-1
U
TYPICAL APPLICATIO S
5V to –5V Inverting Converter
C3
0.47µF
L1
10µH
L2
10µH
V
–5V
IN
5V
100mA
5
1
100pF
V
SW
IN
D1
73.2k
24.9k
C2
10µF
LT1617
4
3
SHDN
NFB
GND
2
C1
4.7µF
C1: TAIYO YUDEN LMK316BJ475
C2: TAIYO YUDEN JMK316BJ106
C3: TAIYO YUDEN EMK212BJ474
L1, L2: MURATA LQH3C100K24
D1: MOTOROLA MBR0520
(408) 573-4150
(408) 573-4150
(408) 573-4150
(814) 237-1431
(800) 441-2447
1617/-1 TA02
–33V Inverting Charge Pump Converter
C3
0.22µF
L1
10µH
D2
V
–33V
20mA
IN
5V
5
1
V
IN
SW
D1
619k
C2
1µF
LT1617
4
3
SHDN
NFB
GND
2
C1
4.7µF
24.9k
C1: TAIYO YUDEN LMK316BJ475
C2: TAIYO YUDEN GMK316BJ105
C3: TAIYO YUDEN GMK212BJ224
L1: MURATA LQH3C100K24
(408) 573-4150
(408) 573-4150
(408) 573-4150
(814) 237-1431
(800) 441-2447
1617/-1 TA03
D1: MOTOROLA MBR0540
1-Cell to –9V Inverting Converter
C3
0.22µF
L1
47µH
L2
47µH
V
–9V
2.5mA
IN
1V TO 1.5V
5
1
V
IN
SW
D1
150k
C2
4.7µF
LT1617-1
4
3
SHDN
NFB
GND
2
C1
4.7µF
24.9k
C1: TAIYO YUDEN LMK316BJ475
C2: TAIYO YUDEN EMK316BJ475
C3: TAIYO YUDEN TMK316BJ224
L1, L2: MURATA LQH3C470K34
(408) 573-4150
(408) 573-4150
(408) 573-4150
(814) 237-1431
(516) 435-1110
1617/-1 TA02
D1: CENTRAL SEMICONDUCTOR CMDSH-3
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 representation that the
interconnection of its circuits as described herein will not infringe on existing patent rights.
7
LT1617/LT1617-1
U
TYPICAL APPLICATIO S
±20V Dual Output Converter with Load Disconnect
D3
20V
4mA
C3
1µF
D2
C5
1µF
C4
1µF
L1
D1
10µH
V
–20V
4mA
IN
1.5V TO 5V
5
1
100pF
V
SW
IN
D4
267k
C2
1µF
LT1617
4
3
SHDN
NFB
GND
2
C1
4.7µF
24.9k
C1: TAIYO YUDEN LMK316BJ475
(408) 573-4150
1617/-1 TA04
C2, C3, C4: TAIYO YUDEN TMK316BJ105 (408) 573-4150
C5: TAIYO YUDEN LMK212BJ105
L1: MURATA LQH3C100K24
D1, D2, D3, D4: MOTOROLA MBR0530
(408) 573-4150
(814) 237-1431
(800) 441-2447
U
Dimensions in millimeters (inches) unless otherwise noted.
PACKAGE DESCRIPTIO
S5 Package
5-Lead Plastic SOT-23
(LTC DWG # 05-08-1633)
2.60 – 3.00
(0.102 – 0.118)
2.80 – 3.00
(0.110 – 0.118)
(NOTE 3)
1.50 – 1.75
(0.059 – 0.069)
0.00 – 0.15
(0.00 – 0.006)
0.90 – 1.45
(0.035 – 0.057)
0.10 – 0.60
(0.004 – 0.024)
REF
0.35 – 0.50
(0.014 – 0.020)
FIVE PLACES (NOTE 2)
0.90 – 1.30
(0.035 – 0.051)
S5 SOT-23 0797
0.09 – 0.20
(0.004 – 0.008)
(NOTE 2)
0.95
(0.037)
REF
1.90
(0.074)
REF
NOTE:
1. DIMENSIONS ARE IN MILLIMETERS
2. DIMENSIONS ARE INCLUSIVE OF PLATING
3. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR
4. MOLD FLASH SHALL NOT EXCEED 0.254mm
5. PACKAGE EIAJ REFERENCE IS SC-74A (EIAJ)
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Burst Mode is a trademark of Linear Technology Corporation
16171f LT/TP 0200 4K • PRINTED IN USA
LINEAR TECHNOLOGY CORPORATION 1999
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
8
●
●
(408)432-1900 FAX:(408)434-0507 www.linear-tech.com
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