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LT1615/LT1615-1 Micropower Step-Up DC/DC Converters in ThinSOT
FEATURES
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DESCRIPTIO
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Low Quiescent Current: 20A in Active Mode <1A 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
APPLICATIO S
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LCD Bias Handheld Computers Battery Backup Digital Cameras
The LT(R)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 20A at no load, which further reduces to 0.5A 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.
, LTC and LT are registered trademarks of Linear Technology Corporation. ThinSOT is a trademark of Linear Technology Corporation.
TYPICAL APPLICATIO
L1 10H
1-Cell Li-Ion to 20V Converter for LCD Bias
85
D1 20V 12mA SW LT1615 SHDN C1 4.7F GND FB R2 130k
1615/-1 TA01
VIN 2.5V TO 4.2V VIN
80 VIN = 4.2V 75
EFFICIENCY (%)
R1 2M C2 1F
70 65 60 55 50 0.1
C1: TAIYO YUDEN LMK316BJ475 C2: TAIYO YUDEN TMK316BJ105 D1: MOTOROLA MBR0530 L1: MURATA LQH3C100K24
0.3
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Efficiency
VIN = 2.5V VIN = 3.3V 1 3 10 LOAD CURRENT (mA) 30
1615/-1 TA01a
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LT1615/LT1615-1
ABSOLUTE
(Note 1)
AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
ORDER PART NUMBER
TOP VIEW SW 1 GND 2 FB 3 4 SHDN 5 VIN
VIN, SHDN Voltage ................................................... 15V SW Voltage .............................................................. 36V FB Voltage .................................................................VIN Current into FB Pin ................................................. 1mA Junction Temperature ........................................... 125C Operating Temperature Range (Note 2) .. - 40C to 85C Storage Temperature Range ................. - 65C to 150C Lead Temperature (Soldering, 10 sec).................. 300C
LT1615ES5 LT1615ES5-1 LT1615IS5 S5 PART MARKING LTIZ LTKH LTXZ
S5 PACKAGE 5-LEAD PLASTIC SOT-23
TJMAX = 125C, JA = 256C/W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
PARAMETER Minimum Input Voltage Quiescent Current FB Comparator Trip Point FB Comparator Hysteresis Output Voltage Line Regulation FB Pin Bias Current (Note 3) Switch Off Time Switch VCESAT Switch Current Limit SHDN Pin Current SHDN Input Voltage High SHDN Input Voltage Low Switch Leakage Current Switch Off, VSW = 5V 1.2V < VIN < 12V VFB = 1.23V VFB > 1V VFB < 0.6V CONDITIONS LT1615-1 LT1615 Not Switching VSHDN = 0V
The q denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = 1.2V, VSHDN = 1.2V unless otherwise noted.
MIN TYP MAX 1.0 1.2 20
q
UNITS V V A A V mV %/V nA ns s
30 1 1.255 0.1 80
1.205
1.23 8 0.05
q
30 400 1.5 85 250 75 300 100 350 2 8 0.9
ISW = 70mA (LT1615-1) ISW = 300mA (LT1615) LT1615-1 LT1615 VSHDN = 1.2V VSHDN = 5V
120 350 125 400 3 12 0.25
0.01
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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 0C to 70C. Specifications over the - 40C to 85C operating temperature range are assured by design,
characterization and correlation with statistical process controls. The LT1615I is guaranteed to meet performance specifications over the -40C to 85C operating temperature range. Note 3: Bias current flows into the FB pin.
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mV mV mA mA A A V V A
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LT1615/LT1615-1 TYPICAL PERFOR A CE CHARACTERISTICS
Switch Saturation Voltage (VCESAT)
0.60 0.55 QUIESCENT CURRENT (A) 0.50 0.45 0.40 0.35 0.30 0.25 0.20 0.15 0.10 -50 -25 0 25 50 TEMPERATURE (C) 75 100 1.20 -50 -25 0 25 50 TEMPERATURE (C) 75 0 100
15 -50 -25 0 25 50 TEMPERATURE (C) 75 100
FEEDBACK VOLTAGE (V) SWITCH VOLTAGE (V)
ISWITCH = 500mA
ISWITCH = 300mA
Switch Off Time
550 500 400 350
SWITCH OFF TIME (ns)
450 400 350 300 250 -50 VIN = 1.2V VIN = 12V
PEAK CURRENT (mA)
300 250 200 150
LT1615
VIN = 1.2V
SHUTDOWN PIN CURRENT (A)
-25
0 25 50 TEMPERATURE (C)
PI FU CTIO S
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. FB (Pin 3): Feedback Pin. Set the output voltage by selecting values for R1 and R2 (see Figure 1): 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.
V R1 = R2 OUT - 1 1.23
UW
75
Feedback Pin Voltage and Bias Current
1.25 50
25
Quiescent Current
VFB = 1.23V NOT SWITCHING
1.24 VOLTAGE 1.23
40
BIAS CURRENT (nA)
23
30
21 VIN = 12V 19 VIN = 1.2V 17
1.22
CURRENT
20
1.21
10
1615/-1 G01
1615/-1 G02
1615/-1 G03
Switch Current Limit
VIN = 12V 25
Shutdown Pin Current
20
15 25C 10 100C 5
LT1615-1 100
VIN = 12V VIN = 1.2V
50 100 0 -50 0 -25 0 25 50 TEMPERATURE (C) 75 100 0 5 10 SHUTDOWN PIN VOLTAGE (V) 15
1615/-1 G03
1615/-1 G04
1615/-1 G05
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LT1615/LT1615-1
BLOCK DIAGRA
VIN
VOUT
R1 (EXTERNAL) R2 (EXTERNAL)
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
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L1 C1 5 D1 VOUT VIN 4 SHDN 1 SW C2 R5 40k R6 40k
+ -
FB 3 Q1 Q2 X10 R3 30k R4 140k
A1 ENABLE
400ns ONE-SHOT DRIVER RESET
Q3
+
0.12 A2
-
42mV* 2 GND
1615/-1 BD
* 12mV FOR LT1615-1
Figure 1. LT1615 Block Diagram
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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 1.5s 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).
LT1615/LT1615-1
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 LQH3C4R7 LQH3C100 LQH3C220 CD43-4R7 CD43-100 CDRH4D18-4R7 CDRH4D18-100 DO1608-472 DO1608-103 DO1608-223 VALUE (H) 4.7 10 22 4.7 10 4.7 10 4.7 10 22 MAX DCR () 0.26 0.30 0.92 0.11 0.18 0.16 0.20 0.09 0.16 0.37 VENDOR Murata (814) 237-1431 www.murata.com Sumida (847) 956-0666 www.sumida.com Coilcraft (847) 639-6400 www.coilcraft.com
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
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VIN value in the above equation. For most systems with output voltages below 7V, a 4.7H 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 21H inductor is called for with the above equation, but a 10H 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.
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V +V L = 2 OUT D ILIM
tOFF
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
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 4.7F 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.
Table 2. Recommended Capacitors
CAPACITOR TYPE Ceramic VENDOR Taiyo Yuden (408) 573-4150 www.t-yuden.com AVX (803) 448-9411 www.avxcorp.com Murata (714) 852-2001 www.murata.com
Ceramic
Ceramic
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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.
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LT1615/LT1615-1
TYPICAL APPLICATIO S
2-Cell to 3.3V Boost Converter
VIN 1.5V TO 3V L1 4.7H 5 VIN LT1615 4 C1 4.7F SHDN GND 2 (408) 573-4150 (408) 573-4150 (814) 237-1431 (800) 441-2447
1615/-1 TA03
D1 1 SW 3 604k 1M C2 22F 3.3V 60mA 4.7pF
EFFICIENCY (%)
FB
C1: TAIYO YUDEN LMK316BJ475 C2: TAIYO YUDEN JMK325BJ226 L1: MURATA LQH3C4R7M24 D1: MOTOROLA MBR0520
1-Cell Li-Ion to 3.3V SEPIC Converter
L1 10H 5 VIN LT1615 4 C1 4.7F SHDN GND 2 (408) 573-4150 (408) 573-4150 (408) 573-4150 (814) 237-1431 (800) 441-2447
1615/-1 TA07
C3 1F 1 SW 3
VIN 2.5V TO 4.2V
FB
C1: TAIYO YUDEN LMK316BJ475 C2: TAIYO YUDEN JMK316BJ106 C3: TAIYO YUDEN JMK107BJ105 L1, L2: MURATA LQH3C100K24 D1: MOTOROLA MBR0520
PIN Diode Driver
VIN 1V TO 6V L1 22H 5 VIN LT1615-1 4 C1 4.7F SHDN GND 2 (408) 573-4150 (408) 573-4150 (814) 237-1431 (800) 441-2447
1615/-1 TA09
D1 1 SW 3 365k 10M C2 1F C1 4.7F 4 35V 500A VIN 1V TO 1.5V 5 VIN
FB
C1: TAIYO YUDEN EMK316BJ475 C2: TAIYO YUDEN GMK316BJ105 L1: MURATA LQH3C220K24 D1: MOTOROLA MBR0540
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.
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2-Cell to 3.3V Converter Efficiency
90 85 80 75 70 65 60 55 50 0.1 1 10 LOAD CURRENT (mA) 100
1615/-1 TA03a
VIN = 3V
VIN = 1.5V
4-Cell to 5V SEPIC Converter
L1 10H 5 VIN C2 10F LT1615 4 C1 4.7F SHDN GND 2 (408) 573-4150 (408) 573-4150 (408) 573-4150 (814) 237-1431 (800) 441-2447
1615/-1 TA07
D1 3.3V 50mA 4.7pF L2 10H 1M VIN 3V TO 6V
C3 1F 1 SW 3
D1 5V 40mA 4.7pF L2 10H 1M C2 10F 324k
FB
604k
C1: TAIYO YUDEN LMK316BJ475 C2: TAIYO YUDEN JMK316BJ106 C3: TAIYO YUDEN JMK107BJ105 L1, L2: MURATA LQH3C100K24 D1: MOTOROLA MBR0520
1-Cell to 3.3V Boost Converter
L1 22H 1 SW LT1615-1 SHDN GND 2 (408) 573-4150 (408) 573-4150 (814) 237-1431 (516) 435-1110
1615/-1 TA04
D1 3.3V 15mA 4.7pF 1M 3 604k C2 10F
FB
C1: TAIYO YUDEN LMK316BJ475 C2: TAIYO YUDEN JMK316BJ106 L1: MURATA LQH3C220K24 D1: CENTRAL SEMICONDUCTOR CMDSH-3
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LT1615/LT1615-1
TYPICAL APPLICATIO S
20V Dual Output Converter with Output Disconnect
D3 -20V 4mA C3 1F
VIN 1.5V TO 5V
PACKAGE DESCRIPTIO
.20 (.008) DATUM `A' A A2 2.60 - 3.00 1.50 - 1.75 (.102 - .118) (.059 - .069) (NOTE 3) 1.90 (.074) REF SOT-23 (Original) .90 - 1.45 (.035 - .057) .00 - .15 (.00 - .006) .90 - 1.30 (.035 - .051) .35 - .55 (.014 - .021) SOT-23 (ThinSOT) 1.00 MAX (.039 MAX) .01 - .10 (.0004 - .004) .80 - .90 (.031 - .035) .30 - .50 REF (.012 - .019 REF) A1
L NOTE: 1. CONTROLLING DIMENSION: MILLIMETERS MILLIMETERS 2. DIMENSIONS ARE IN (INCHES)
.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
RELATED PARTS
PART NUMBER LT1307 LT1316 LT1317 LT1610 LT1611 LT1613 LT1617 DESCRIPTION Single-Cell Micropower 600kHz PWM DC/DC Converter Burst ModeTM Operation DC/DC with Programmable Current Limit 2-Cell Micropower DC/DC with Low-Battery Detector Single-Cell Micropower DC/DC Converter 1.4MHz Inverting Switching Regulator in 5-Lead ThinSOT 1.4MHz Switching Regulator in 5-Lead ThinSOT Micropower Inverting DC/DC Converter in 5-Lead ThinSOT COMMENTS 3.3V at 75mA from One Cell, MSOP Package 1.5V Minimum, Precise Control of Peak Current Limit 3.3V at 200mA from Two Cells, 600kHz Fixed Frequency 3V at 30mA from 1V, 1.7MHz Fixed Frequency - 5V at 150mA from 5V Input, Tiny ThinSOT Package 5V at 200mA from 3.3V Input, Tiny ThinSOT Package -15V at 12mA from 2.5V Input, Tiny ThinSOT Package
Burst Mode is a trademark of Linear Technology Corporation
8
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408)432-1900 q FAX: (408) 434-0507 q www.linear-tech.com
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D2 C4 1F L1 10H 5 VIN LT1615 4 C1 4.7F SHDN GND 2 (408) 573-4150 (408) 573-4150 (408) 573-4150 (814) 237-1431 (800) 441-2447 FB 3 130k 1 SW D4 2M C5 1F
D1 20V 4mA 4.7pF C2 1F
C1: TAIYO YUDEN LMK316BJ475 C2, C3, C4: TAIYO YUDEN TMK316BJ105 C5: TAIYO YUDEN LMK212BJ105 L1: MURATA LQH3C100K24 D1, D2, D3, D4: MOTOROLA MBR0530
1615/-1 TA05
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)
PIN ONE .95 (.037) REF
A A1 A2 L
.25 - .50 (.010 - .020) (5PLCS, NOTE 2)
S5 SOT-23 0401
16151fa LT/TP 0601 1.5K REV A * PRINTED IN USA
(c) LINEAR TECHNOLOGY CORPORATION 1998

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