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LT1617/LT1617-1 Micropower Inverting DC/DC Converters in SOT-23
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 Tiny 5-Lead SOT-23 Package
APPLICATIO S
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LCD Bias Handheld Computers Battery Backup Digital Cameras
The LT(R)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 20A at no load, which further reduces to 0.5A in shutdown. A current limited, fixed offtime 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 without the use of costly transformers. 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.
TYPICAL APPLICATION
1-Cell Li-Ion to -15V Inverting Converter
L1 22H 5 VIN LT1617 4 C1 4.7F SHDN GND 2 NFB 3 24.9k C3 0.22F 1 SW D1 267k C2 4.7F L2 22H
80
-15V 12mA EFFICIENCY (%)
VIN 2.5V TO 4.2V
75 70 65 60 55
C1: TAIYO YUDEN LMK316BJ475 C2: TAIYO YUDEN EMK316BJ475 C3: TAIYO YUDEN TMK316BJ224 L1, L2: MURATA LQH3C220K34 D1: MOTOROLA MBR0530
1617/-1 TA01
50 0.1
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Efficiency
VIN = 4.2V VIN = 2.5V 1 10 LOAD CURRENT (mA) 30
1617/-1 TA01a
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LT1617/LT1617-1
ABSOLUTE
(Note 1)
AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW SW 1 GND 2 NFB 3 4 SHDN 5 VIN
VIN, SHDN Voltage ................................................... 15V SW Voltage .............................................................. 36V NFB Voltage ............................................................. - 3V Current into NFB 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
ORDER PART NUMBER LT1617ES5 LT1617ES5-1 S5 PART MARKING LTKF LTKA
S5 PACKAGE 5-LEAD PLASTIC SOT-23
TJMAX = 125C, JA = 256C/W
Consult factory for Industrial and Military grade parts.
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 VNFB = -1.23V CONDITIONS LT1617-1 LT1617 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 A ns mV mV mA mA A A V V A
30 1 -1.255 0.1 2.7 120 350 125 400 3 12 0.25
-1.205
-1.23 8 0.05
q
1.3
2 400 85 250
ISW = 60mA (LT1617-1) ISW = 300mA (LT1617) LT1617-1 LT1617 VSHDN = 1.2V VSHDN = 5V 0.9 75 300
100 350 2 8
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 LT1617 and LT1617-1 are guaranteed to meet 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. Note 3: Bias current flows out of the NFB pin.
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LT1617/LT1617-1 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)
300 250 200 150
LT1617
VIN = 1.2V
SHUTDOWN PIN CURRENT (A)
SWITCH CURRENT LIMIT (mA)
450 400 350 300 250 -50 VIN = 1.2V VIN = 12V
-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. NFB (Pin 3): Feedback Pin. Set the output voltage by selecting values for R1 and R2 (see Figure 1):
R1 = VOUT - 1.23 1.23 + 2 * 10 -6 R2
UW
75
Feedback Pin Voltage and Bias Current
-1.25 5
25
Quiescent Current
VFB = 1.23V NOT SWITCHING
-1.24 VOLTAGE -1.23
4 BIAS CURRENT (A)
23
3
21 VIN = 12V 19 VIN = 1.2V 17
-1.22 CURRENT -1.21
2
1
1617/-1 G01
1617/-1 G02
1617/-1 G03
Switch Current Limit
VIN = 12V 25
Shutdown Pin Current
20
15 25C 10 100C 5
LT1617-1 100
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
1617/-1 G06
1617/-1 G04
1617/-1 G05
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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.
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LT1617/LT1617-1
BLOCK DIAGRA
VIN
VOUT R1 (EXTERNAL) R2 (EXTERNAL)
NFB
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 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 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
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L1 C1 5 C3 L2 VOUT VIN 4 SHDN 1 SW D1 C2 R5 80k R6 80k
+ -
Q1 Q2 X10 R3 60k R4 280k 3
A1 ENABLE
400ns ONE-SHOT DRIVER RESET
Q3
+
0.12 A2
-
42mV* 2 GND
1617/-1 BD
* 12mV FOR LT1617-1
Figure 1. LT1617 Block Diagram
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inductors L1 and L2 begins ramping up. Once the switch current reaches 350mA, comparator A2 resets the oneshot, 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 oneshot. 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).
LT1617/LT1617-1
APPLICATIO S I FOR ATIO
Choosing an Inductor
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 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 D01608-223 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 VENDOR Murata (714) 852-2001 www.murata.com Sumida (847) 956-0666 www.sumida.com 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 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:
VOUT + VD L = 2 ILIM
tOFF
where VD = 0.4V (Schottky diode voltage), ILIM = 350mA or 100mA, and tOFF = 400ns.
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For higher output voltages, the formula above will give large inductance values. For a 2V to 20V converter (typical LCD bias application), a 47H inductor is called for with the above equation, but a 10H or 22H inductor could be used without excessive reduction in maximum output current. 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. 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.
L= VOUT - VIN(MIN) + VD ILIM tOFF
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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:
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 induc-
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LT1617/LT1617-1
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 overshoot 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. 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 LT1617'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 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 4.7F 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 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 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 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 100pF feed-forward capacitor 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.
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LT1617/LT1617-1
TYPICAL APPLICATIO S
5V to - 5V Inverting Converter
L1 10H 5 VIN LT1617 4 C1 4.7F SHDN GND 2 NFB 3 24.9k C3 0.47F 1 SW D1 73.2k C2 10F L2 10H 100pF
VIN 5V
C1: TAIYO YUDEN LMK316BJ475 C2: TAIYO YUDEN JMK316BJ106 C3: TAIYO YUDEN EMK212BJ474 L1, L2: MURATA LQH3C100K24 D1: MOTOROLA MBR0520
VIN 5V
VIN 1V TO 1.5V
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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-5V 100mA
(408) 573-4150 (408) 573-4150 (408) 573-4150 (814) 237-1431 (800) 441-2447
1617/-1 TA02
- 33V Inverting Charge Pump Converter
L1 10H 5 VIN LT1617 4 C1 4.7F SHDN GND 2 NFB 3 24.9k 1 SW D1 619k C2 1F C3 0.22F D2 -33V 20mA
C1: TAIYO YUDEN LMK316BJ475 C2: TAIYO YUDEN GMK316BJ105 C3: TAIYO YUDEN GMK212BJ224 L1: MURATA LQH3C100K24 D1: MOTOROLA MBR0540
(408) 573-4150 (408) 573-4150 (408) 573-4150 (814) 237-1431 (800) 441-2447
1617/-1 TA03
1-Cell to - 9V Inverting Converter
L1 47H 5 VIN LT1617-1 4 C1 4.7F SHDN GND 2 NFB 3 24.9k C3 0.22F 1 SW D1 150k C2 4.7F L2 47H
-9V 2.5mA
C1: TAIYO YUDEN LMK316BJ475 C2: TAIYO YUDEN EMK316BJ475 C3: TAIYO YUDEN TMK316BJ224 L1, L2: MURATA LQH3C470K34 D1: CENTRAL SEMICONDUCTOR CMDSH-3
(408) 573-4150 (408) 573-4150 (408) 573-4150 (814) 237-1431 (516) 435-1110
1617/-1 TA02
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LT1617/LT1617-1
TYPICAL APPLICATIO S
20V Dual Output Converter with Load Disconnect
D3 20V 4mA C3 1F
VIN 1.5V TO 5V
PACKAGE DESCRIPTIO
2.60 - 3.00 (0.102 - 0.118) 1.50 - 1.75 (0.059 - 0.069) 0.00 - 0.15 (0.00 - 0.006) 0.90 - 1.45 (0.035 - 0.057) 2.80 - 3.00 (0.110 - 0.118) (NOTE 3)
0.10 - 0.60 (0.004 - 0.024) REF
0.09 - 0.20 (0.004 - 0.008) (NOTE 2)
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)
RELATED PARTS
PART NUMBER LT1307 LT1316 LT1317 LT1610 LT1611 LT1613 LT1615 DESCRIPTION Single-Cell Micropower 600kHz PWM DC/DC Converter Burst Mode 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 SOT-23 1.4MHz Switching Regulator in 5-Lead SOT-23 Micropower DC/DC Converter in 5-Lead SOT-23
TM
Burst Mode is a trademark of Linear Technology Corporation
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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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C5 1F L1 10H 5 VIN LT1617 4 C1 4.7F SHDN GND 2 NFB 3 1 SW
D2 C4 1F
D1 -20V 4mA 100pF D4 267k C2 1F 24.9k (408) 573-4150 (408) 573-4150 (408) 573-4150 (814) 237-1431 (800) 441-2447
C1: TAIYO YUDEN LMK316BJ475 C2, C3, C4: TAIYO YUDEN TMK316BJ105 C5: TAIYO YUDEN LMK212BJ105 L1: MURATA LQH3C100K24 D1, D2, D3, D4: MOTOROLA MBR0530
1617/-1 TA04
Dimensions in millimeters (inches) unless otherwise noted. S5 Package 5-Lead Plastic SOT-23
(LTC DWG # 05-08-1633)
0.35 - 0.50 0.90 - 1.30 (0.014 - 0.020) (0.035 - 0.051) FIVE PLACES (NOTE 2) S5 SOT-23 0797
1.90 (0.074) REF
0.95 (0.037) REF
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 fro 1V, 1.7MHz Fixed Frequency - 5V at 150mA from 5V Input, Tiny SOT-23 Package 5V at 200mA from 3.3V Input, Tiny SOT-23 Package 20V at 12mA from 2.5V Input, Tiny SOT-23 Package
16171f LT/TP 0200 4K * PRINTED IN USA
(c) LINEAR TECHNOLOGY CORPORATION 1999

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