LT1615/LT1615-1 - Micropower Step-Up DC/DC Converters in ThinSOT

LT1615/LT1615-1
Micropower Step-Up
DC/DC Converters
in ThinSOT
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DESCRIPTIO
FEATURES
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The LT®1615/LT1615-1 are micropower step-up DC/DC
converters in a 5-lead low profile (1mm) ThinSOT package. The LT1615 is designed for higher power systems
with a 350mA current limit and an input voltage range of
1.2V to 15V, whereas the LT1615-1 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, resulting in high efficiency over a broad
range of load current. The 36V switch allows high voltage
outputs up to 34V to be easily generated in a simple boost
topology without the use of costly transformers. The
LT1615’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.
Low Quiescent Current:
20µA 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
Low Profile (1mm) ThinSOTTM Package
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APPLICATIO S
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LCD Bias
Handheld Computers
Battery Backup
Digital Cameras
, LTC and LT are registered trademarks of Linear Technology Corporation.
ThinSOT is a trademark of Linear Technology Corporation.
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TYPICAL APPLICATIO
1-Cell Li-Ion to 20V Converter for LCD Bias
Efficiency
85
L1
10µH
VIN
2.5V TO 4.2V
D1
80
20V
12mA
VIN = 4.2V
VIN
SW
R1
2M
C2
1µF
LT1615
FB
SHDN
C1
4.7µF
GND
C1: TAIYO YUDEN LMK316BJ475
C2: TAIYO YUDEN TMK316BJ105
D1: MOTOROLA MBR0530
L1: MURATA LQH3C100K24
R2
130k
EFFICIENCY (%)
75
VIN = 2.5V
70
VIN = 3.3V
65
60
1615/-1 TA01
55
50
0.1
0.3
1
3
10
LOAD CURRENT (mA)
30
1615/-1 TA01a
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LT1615/LT1615-1
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ABSOLUTE
AXI U RATI GS
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PACKAGE/ORDER I FOR ATIO
(Note 1)
VIN, SHDN Voltage ................................................... 15V
SW Voltage .............................................................. 36V
FB Voltage .................................................................VIN
Current into FB 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
ORDER PART
NUMBER
LT1615ES5
LT1615ES5-1
LT1615IS5
LT1615IS5-1
TOP VIEW
SW 1
5 VIN
GND 2
FB 3
4 SHDN
S5 PACKAGE
5-LEAD PLASTIC SOT-23
S5 PART MARKING
TJMAX = 125°C, θJA = 256°C/W
LTIZ
LTKH
LTXZ
LTBHT
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 1.2V, VSHDN = 1.2V unless otherwise noted.
PARAMETER
CONDITIONS
Minimum Input Voltage
LT1615-1
LT1615
Quiescent Current
Not Switching
VSHDN = 0V
FB Comparator Trip Point
MIN
●
1.205
FB Comparator Hysteresis
TYP
MAX
UNITS
1.0
1.2
V
V
20
30
1
µA
µA
1.23
1.255
V
8
mV
Output Voltage Line Regulation
1.2V < VIN < 12V
FB Pin Bias Current (Note 3)
VFB = 1.23V
Switch Off Time
VFB > 1V
VFB < 0.6V
400
1.5
Switch VCESAT
ISW = 70mA (LT1615-1)
ISW = 300mA (LT1615)
85
250
120
350
mV
mV
Switch Current Limit
LT1615-1
LT1615
100
350
125
400
mA
mA
SHDN Pin Current
VSHDN = 1.2V
VSHDN = 5V
2
8
3
12
µA
µA
SHDN Input Voltage High
●
75
300
0.05
0.1
%/V
30
80
nA
0.9
V
SHDN Input Voltage Low
Switch Leakage Current
ns
µs
Switch Off, VSW = 5V
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: The LT1615E and LT1615E-1 are 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,
0.01
0.25
V
5
µA
characterization and correlation with statistical process controls. The
LT1615I/LT1615I-1 is guaranteed to meet performance specifications over
the –40°C to 85°C operating temperature range.
Note 3: Bias current flows into the FB pin.
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LT1615/LT1615-1
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TYPICAL PERFOR A CE CHARACTERISTICS
Switch Saturation Voltage
(VCESAT)
Feedback Pin Voltage and
Bias Current
0.60
Quiescent Current
1.25
50
25
40
23
VFB = 1.23V
NOT SWITCHING
FEEDBACK VOLTAGE (V)
1.24
0.45
ISWITCH = 500mA
0.40
0.35
0.30
ISWITCH = 300mA
0.25
0.20
VOLTAGE
1.23
30
CURRENT
1.22
20
1.21
10
BIAS CURRENT (nA)
SWITCH VOLTAGE (V)
0.50
QUIESCENT CURRENT (µA)
0.55
21
VIN = 12V
19
VIN = 1.2V
17
0.15
–25
0
25
50
TEMPERATURE (°C)
75
1.20
–50
100
–25
0
25
50
TEMPERATURE (°C)
1615/-1 G01
400
PEAK CURRENT (mA)
VIN = 1.2V
VIN = 12V
350
250
–50
75
300
VIN = 1.2V
LT1615
250
200
150
LT1615-1
100
25
VIN = 12V
VIN = 12V
100
VIN = 1.2V
300
0
25
50
TEMPERATURE (°C)
Shutdown Pin Current
350
500
450
–25
1615/-1 G03
Switch Current Limit
550
400
15
–50
0
100
1615/-1 G02
Switch Off Time
SWITCH OFF TIME (ns)
75
SHUTDOWN PIN CURRENT (µA)
0.10
–50
20
15
25°C
10
100°C
5
50
–25
0
25
50
TEMPERATURE (°C)
75
100
0
–50
0
–25
0
25
50
TEMPERATURE (°C)
1615/-1 G04
75
100
1615/-1 G05
0
5
10
SHUTDOWN PIN VOLTAGE (V)
15
1615/-1 G03
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SW (Pin 1): Switch Pin. This is the collector of the internal
NPN power switch. Minimize the metal trace area connected to this pin to minimize EMI.
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
to enable the device. Tie below 0.25V to turn off the device.
VIN (Pin 5): Input Supply Pin. Bypass this pin with a
capacitor as close to the device as possible.
FB (Pin 3): Feedback Pin. Set the output voltage by
selecting values for R1 and R2 (see Figure 1):
V

R1 = R2  OUT − 1
 1.23 
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LT1615/LT1615-1
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BLOCK DIAGRA
D1
L1
VOUT
VIN
C1
5
VIN
R5
40k
4
SHDN
1
C2
SW
R6
40k
+
A1
ENABLE
VOUT
–
R1
(EXTERNAL)
R2
(EXTERNAL)
FB
3
Q1
Q2
X10
400ns
ONE-SHOT
Q3
DRIVER
R3
30k
RESET
+
R4
140k
0.12Ω
A2
–
42mV*
2
GND
1615/-1 BD
* 12mV FOR LT1615-1
Figure 1. LT1615 Block Diagram
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OPERATIO
The LT1615 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
the block diagram in Figure 1. Q1 and Q2 along with R3 and
R4 form a bandgap reference used to regulate the output
voltage. When the voltage at the FB pin is slightly above
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 FB 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 oneshot, 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 oneshot, again allowing L1 to deliver current to the output.
This switching action continues until the output voltage is
charged up (until the FB pin reaches 1.23V), then A1 turns
off the internal circuitry and the cycle repeats. The LT1615
contains additional circuitry to provide protection during
start-up and under short-circuit conditions. When the FB
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 LT1615 power switch and in
the external inductor and diode. The LT1615-1 operates in
the same manner, except the switch current is limited to
100mA (the A2 reference voltage is 12mV instead of
42mV).
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LT1615/LT1615-1
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APPLICATIO S I FOR ATIO
Choosing an Inductor
Several recommended inductors that work well with the
LT1615 and LT1615-1 are listed in Table 1, although there
are many other 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. Use the equations
and recommendations in the next few sections to find the
correct inductance value for your design.
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
(814) 237-1431
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
DO1608-472
DO1608-103
DO1608-223
4.7
10
22
0.09
0.16
0.37
Coilcraft
(847) 639-6400
www.coilcraft.com
VIN value in the above equation. For most systems with
output 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).
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.
Inductor Selection—SEPIC Regulator
The formula below calculates the approximate inductor
value to be used for a SEPIC regulator using the LT1615.
As for the boost inductor selection, a larger or smaller
value can be used.
V
+V
L = 2  OUT D
 ILIM

 tOFF

Inductor Selection—Boost Regulator
The formula below calculates the appropriate inductor
value to be used for a boost regulator using the LT1615 or
LT1615-1 (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 increase 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:
L=
VOUT − VIN(MIN) + VD
ILIM
tOFF
where VD = 0.4V (Schottky diode voltage), ILIM = 350mA or
100mA, and tOFF = 400ns; for designs with varying VIN
such as battery powered applications, use the minimum
Current Limit Overshoot
For the constant off-time control scheme of the LT1615,
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:
 VIN(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 inductor 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
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LT1615/LT1615-1
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APPLICATIO S I FOR ATIO
input voltages greater than 5V), the current limit overshoot can be quite high. Although it is internally current
limited to 350mA, the power switch of the LT1615 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 LT1615 and below
400mA for the LT1615-1.
Capacitor Selection
Low ESR (Equivalent Series Resistance) capacitors should
be used at the output to minimize the output ripple voltage.
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 LT1615’s SOT-23 package. Solid tantalum capacitors (like the AVX TPS, Sprague 593D families) or OS-CON
capacitors can be used, but they will occupy more board
area than a ceramic and will have a higher 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 LT1615. A 4.7µF input capacitor is sufficient 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.
Diode Selection
For most LT1615 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
LT1615. 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 0.35A. For LT1615-1 applications, a Philips BAT54 or Central Semiconductor CMDSH-3
works well.
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 LT1615 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
output capacitor value or add a 4.7pF feed-forward capacitor in the feedback network of the LT1615 (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
AVX
(803) 448-9411
www.avxcorp.com
Ceramic
Murata
(714) 852-2001
www.murata.com
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LT1615/LT1615-1
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TYPICAL APPLICATIO S
2-Cell to 3.3V Converter Efficiency
2-Cell to 3.3V Boost Converter
L1
4.7µH
90
D1
5
1
VIN
SW
3.3V
60mA
FB
SHDN
C2
22µF
3
GND
C1
4.7µF
VIN = 3V
80
1M
LT1615
4
85
4.7pF
EFFICIENCY (%)
VIN
1.5V TO 3V
604k
2
75
VIN = 1.5V
70
65
60
C1: TAIYO YUDEN LMK316BJ475
C2: TAIYO YUDEN JMK325BJ226
L1: MURATA LQH3C4R7M24
D1: MOTOROLA MBR0520
(408) 573-4150
(408) 573-4150
(814) 237-1431
(800) 441-2447
1615/-1 TA03
55
50
0.1
1
10
LOAD CURRENT (mA)
100
1615/-1 TA03a
4-Cell to 5V SEPIC Converter
1-Cell Li-Ion to 3.3V SEPIC Converter
C3
1µF
L1
10µH
VIN
2.5V TO 4.2V
5
1
VIN
SW
3.3V
50mA
LT1615
4
FB
SHDN
1M
C2
10µF
3
GND
C1
4.7µF
VIN
3V TO 6V
4.7pF
L2
10µH
(408) 573-4150
(408) 573-4150
(408) 573-4150
(814) 237-1431
(800) 441-2447
L1
22µH
C1
4.7µF
SW
SHDN
1
VIN
SW
FB
GND
1M
C2
10µF
3
GND
324k
2
C1: TAIYO YUDEN LMK316BJ475
C2: TAIYO YUDEN JMK316BJ106
C3: TAIYO YUDEN JMK107BJ105
L1, L2: MURATA LQH3C100K24
D1: MOTOROLA MBR0520
1615/-1 TA07
35V
500µA
(408) 573-4150
(408) 573-4150
(408) 573-4150
(814) 237-1431
(800) 441-2447
L1
22µH
VIN
1V TO 1.5V
10M
1615/-1 TA07
(408) 573-4150
(408) 573-4150
(814) 237-1431
(800) 441-2447
4
C1
4.7µF
2
1615/-1 TA09
D1
5
1
VIN
SW
3.3V
15mA
4.7pF
1M
C2
10µF
LT1615-1
C2
1µF
3
365k
C1: TAIYO YUDEN EMK316BJ475
C2: TAIYO YUDEN GMK316BJ105
L1: MURATA LQH3C220K24
D1: MOTOROLA MBR0540
4.7pF
L2
10µH
FB
D1
5
SHDN
VIN
5V
40mA
1-Cell to 3.3V Boost Converter
LT1615-1
4
1
C1
4.7µF
604k
PIN Diode Driver
VIN
1V TO 6V
5
D1
LT1615
4
2
C1: TAIYO YUDEN LMK316BJ475
C2: TAIYO YUDEN JMK316BJ106
C3: TAIYO YUDEN JMK107BJ105
L1, L2: MURATA LQH3C100K24
D1: MOTOROLA MBR0520
C3
1µF
L1
10µH
D1
FB
SHDN
3
GND
604k
2
C1: TAIYO YUDEN LMK316BJ475
C2: TAIYO YUDEN JMK316BJ106
L1: MURATA LQH3C220K24
D1: CENTRAL SEMICONDUCTOR CMDSH-3
(408) 573-4150
(408) 573-4150
(814) 237-1431
(516) 435-1110
1615/-1 TA04
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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
LT1615/LT1615-1
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TYPICAL APPLICATIO S
±20V Dual Output Converter with Output Disconnect
D3
–20V
4mA
C3
1µF
D2
C4
1µF
C5
1µF
L1
10µH
VIN
1.5V TO 5V
5
D1
20V
4mA
1
VIN
4.7pF
SW
D4
2M
C2
1µF
LT1615
4
FB
SHDN
3
GND
C1
4.7µF
130k
2
C1: TAIYO YUDEN LMK316BJ475
C2, C3, C4: TAIYO YUDEN TMK316BJ105
C5: TAIYO YUDEN LMK212BJ105
L1: MURATA LQH3C100K24
D1, D2, D3, D4: MOTOROLA MBR0530
(408) 573-4150
(408) 573-4150
(408) 573-4150
(814) 237-1431
(800) 441-2447
1615/-1 TA05
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PACKAGE DESCRIPTIO
S5 Package
5-Lead Plastic SOT-23
(Reference LTC DWG # 05-08-1633)
(Reference LTC DWG # 05-08-1635)
2.80 – 3.10
(.110 – .118)
(NOTE 3)
.20
(.008)
A A2
DATUM ‘A’
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NOTE:
1. CONTROLLING DIMENSION: MILLIMETERS
MILLIMETERS
2. DIMENSIONS ARE IN
(INCHES)
2.60 – 3.00
1.50 – 1.75
(.102 – .118) (.059 – .069)
(NOTE 3)
1.90
(.074)
REF
.09 – .20
(.004 – .008)
(NOTE 2)
3. DRAWING NOT TO SCALE
4. DIMENSIONS ARE INCLUSIVE OF PLATING
5. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR
6. MOLD FLASH SHALL NOT EXCEED .254mm
7. PACKAGE EIAJ REFERENCE IS:
SC-74A (EIAJ) FOR ORIGINAL
JEDEL MO-193 FOR THIN
A1
A
SOT-23
(Original)
.90 – 1.45
(.035 – .057)
SOT-23
(ThinSOT)
1.00 MAX
(.039 MAX)
A1
.00 – .15
(.00 – .006)
.01 – .10
(.0004 – .004)
A2
.90 – 1.30
(.035 – .051)
.80 – .90
(.031 – .035)
L
.35 – .55
(.014 – .021)
.30 – .50 REF
(.012 – .019 REF)
PIN ONE
.95
(.037)
REF
.25 – .50
(.010 – .020)
(5PLCS, NOTE 2)
S5 SOT-23 0401
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Burst Mode is a trademark of Linear Technology Corporation
sn16151 16151fas
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Linear Technology Corporation
16151fa LT/TP 0601 1.5K REV A • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408)432-1900 ● FAX: (408) 434-0507 ● www.linear-tech.com
 LINEAR TECHNOLOGY CORPORATION 1998