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LT3483 Inverting Micropower DC/DC Converter with Schottky in ThinSOT Package
FEATURES

DESCRIPTIO

Internal 40V Schottky Diode One Resistor Feedback (Other Resistor Inside) Internal 40V, 200mA Power Switch Generates Regulated Negative Outputs to -38V Low Quiescent Current: 40A in Active Mode <1A 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
APPLICATIO S

LCD Bias Handheld Computers Battery Backup Digital Cameras OLED Bias
The LT(R)3483 is a micropower inverting DC/DC converter with integrated Schottky and one resistor feedback. The small package size, high level of integration and use of tiny surface mount components yield a solution size as small as 40mm2. The device features a quiescent current of only 40A at no load, which further reduces to 0.1A in shutdown. A current limited, fixed off-time control scheme conserves operating current, resulting in high efficiency over a broad range of load current. A precisely trimmed 10A 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. The LT3483 is available in the low profile (1mm) SOT-23 (ThinSOTTM) package.
, LTC and LT are registered trademarks of Linear Technology Corporation. ThinSOT is a trademark of Linear Technology Corporation. Patent pending.
TYPICAL APPLICATIO
0.22F
3.6V to -8V DC/DC Converter
75 VIN 3.6V 10H
Efficiency and Power Loss
VIN = 3.6V EFFICIENCY 1000
10 VIN 4.7F LT3483 SHDN FB GND D 5pF 806k
EFFICIENCY (%)
70 VOUT -8V 25mA 2.2F
SW
65 POWER LOSS 60
3483 TA01a
55 0.1 1 10 LOAD CURRENT (mA)
U
100
POWER LOSS (mW)
U
U
10
1
0.1 100
3483 TA01b
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1
LT3483
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
ORDER PART NUMBER
TOP VIEW SW 1 GND 2 FB 3 6 VIN 5D 4 SHDN
VIN Voltage ............................................................. 16V SW Voltage ............................................................. 40V D Voltage .............................................................. -40V FB Voltage ............................................................. 2.5V SHDN Voltage ......................................................... 16V Operating Ambient Temperature Range (Note 2) .................................................. - 40C to 85C Junction Temperature .......................................... 125C Storage Temperature Range ................ - 65C to 150C Lead Temperature (Soldering, 10 sec)................. 300C
LT3483ES6
S6 PACKAGE 6-LEAD PLASTIC TSOT-23
TJMAX = 125C, JA = 256C/W IN FREE AIR JA = 120C/W ON BOARD OVER GROUND PLANE
S6 PART MARKING LTBKX
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 = 25C. VIN = 3.6V, VSHDN = 3.6V unless otherwise specified.
PARAMETER VIN Operating Range VIN Undervoltage Lockout FB Comparator Trip Voltage to GND (VFB) FB Output Current (Note 3) FB Comparator Hysteresis Quiescent Current in Shutdown Quiescent Current (Not Switching) IFB Line Regulation Switch Off-Time Switch Current Limit Switch VCESAT Switch Leakage Current Rectifier Leakage Current Rectifier Forward Drop SHDN Input Low Voltage SHDN Input High Voltage SHDN Pin Current Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: The LTC3483E is 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: Current flows out of the pin. 1.5 6 10 ISW = 150mA to GND SW = 40V D = - 40V ID = 150mA to GND 0.64 0.4 170 FB Falling FB = VFB - 5mV FB Rising VSHDN = GND FB = -0.05V 2.5V VIN 16V 300 200 200 1 4 230 40

CONDITIONS
MIN 2.5
TYP 2
MAX 16 2.4 12 -9.75 1 50 0.07
UNITS V V mV A mV A A %/V ns mA mV A A V V V A
0 -10.15
5 -10 10
2
U
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W
U
U
WW
W
LT3483 TYPICAL PERFOR A CE CHARACTERISTICS
VFB Current
10.2 12
SWITCH OFF TIME (ns)
10.1 VFB CURRENT (A) VFB VOLTAGE (mV)
10.0
9.9
9.8 -50
-20
40 10 TEMPERATURE (C)
Switch Current Limit
230 220 210 200 190 180 170 -50
QUIESCENT CURRENT (A)
40
SHDN PIN BIAS CURRENT (A)
SWITCH CURRENT LIMIT (mA)
-20
10 40 TEMPERATURE (C)
PI FU CTIO S
SW: Switch. Connect to external inductor L1 and positive terminal of transfer capacitor. GND: Ground. FB: Feedback. Place resistor to negative output here. Set resistor value R1 = VOUT/10A. SHDN: Shutdown. Connect to GND to turn device off. Connect to supply to turn device on. D: Anode Terminal of Integrated Schottky Diode. Connect to negative terminal of transfer capacitor and external inductor L2 (flyback configuration) or to cathode of external Schottky diode (inverting charge pump configuration). VIN: Input Supply. Must be locally bypassed with 1F or greater.
UW
70
3483 G01
VFB Voltage
400 350 9 300 250 200 150 100 50 100 0 -50 -20 40 10 TEMPERATURE (C) 70 100
3483 G02
Switch Off Time
6
3
0 -50
-20
10 40 TEMPERATURE (C)
70
100
3483 G03
Quiescent Current
50 10
SHDN Pin Bias Current
TA = 25C
8
30
6
20
4
10 NOT SWITCHING VFB = -0.05V
2
70
100
3483 G04
0 -50
-20
40 10 TEMPERATURE (C)
70
100
3483 G05
0
0
8 4 12 SHDN PIN VOLTAGE (V)
16
3483 G06
U
U
U
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3
LT3483
BLOCK DIAGRA W
L1A VIN L1B
*
CFLY
*
VOUT COUT
6 VIN 1.250V REFERENCE 125k R1 VOUT 3 FB 300ns DELAY S R Q Q
1 SW
5 D
Q1
D1 25mV
+
A3
+
A2
-
A1
+
0.1 0.1
-
20mV
-
GND 2 OPTIONAL CHARGE PUMP CONFIGURATION. L1B REPLACED WITH: D2 D R2 VOUT
3483 BD
OPERATIO
The LT3483 uses a constant off-time control scheme to provide high efficiency over a wide range of output currents. Operation can be best understood by referring to the Block Diagram. When the voltage at the FB pin is approximately 0V, comparator A3 disables most of the internal circuitry. Output current is then provided by external capacitor COUT, which slowly discharges until the voltage at the FB pin goes above the hysteresis point of A3. Typical hysteresis at the FB pin is 10mV. A3 then enables the internal circuitry, turns on power switch Q1, and the currents in external inductors L1A and L1B begin to ramp up. Once the
4
U
switch current reaches 200mA, comparator A1 resets the latch, which turns off Q1 after about 80ns. Inductor current flows through the internal Schottky D1 to GND, charging 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 the output capacitor charge is replenished (until the FB pin decreases to 0V), then A3 turns off the internal circuitry and the cycle repeats. The inverting charge pump topology replaces L1B with the series combination D2 and R2.
3483f
LT3483
APPLICATIO S I FOR ATIO
CHOOSING A REGULATOR TOPOLOGY Inverting Charge Pump
The inverting charge pump regulator combines an inductor-based step-up with an inverting charge pump. This configuration usually provides the best size, efficiency and output ripple and is applicable where the magnitude of VOUT 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 of this resistor is to smooth/reduce the current spike in the flying capacitor when the switch turns on. A 10 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. Inverting Flyback The inverting flyback regulator, shown in the -5V application 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 occupies more board space compared with the inverting charge 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 0.47F capacitor may be added between terminals D and SW of LT3483 to suppress ringing at SW.
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Inductor Selection Several recommended inductors that work well with the LT3483 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. For inverting charge pump regulators with input and output voltages below 7V, a 4.7H or 6.8H 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 10H 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 recommended, as too large of an inductance will increase the output voltage ripple without providing much additional output current.
Table 1. Recommended Inductors
L PART (H) LQH2MCN4R7M02L 4.7 LQH2MCN6R8M02L 6.8 LQH2MCN100M02L 10 SDQ12 10 Coupled 15 Inductor 744876 10 Coupled Inductor MAX IDC (mA) 300 255 225 980 780 550 DCR () 0.84 1.0 1.2 0.72 1.15 0.46 HEIGHT (mm) MANUFACTURER 0.95 Murata www.murata.com 1.2 Cooper Electronics Tech www.cooperet.com Wurth Elektronik www.we-online.com 1.2
W
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Capacitor Selection The small size and low ESR of ceramic capacitors make them ideal for LT3483 applications. Use of X5R and X7R types is recommended because they retain their capacitance over wider voltage and temperature ranges than other dielectric types. Always verify the proper voltage rating. 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 4.7F 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 1F is adequate.
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5
LT3483
APPLICATIO S I FOR ATIO
A capacitor in parallel with feedback resistor R1 is recommended 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 configurations. Output voltage ripple can be reduced to 20mV in some cases using this capacitor in combination with an appropriately selected output capacitor. The output capacitor is selected based on desired output voltage ripple. For low output voltage ripple in the inverting flyback configuration, use a 4.7F to 10F capacitor. The inverting charge pump utilizes values ranging from 0.22F to 4.7F. The following formula is useful to estimate the output capacitor value needed:
COUT L * ISW2 = - VOUT * VOUT
where ISW = 0.25A and VOUT = 30mV. The flying capacitor in the inverting charge pump configuration ranges from 0.1F to 0.47F. 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 Kemet Murata Taiyo Yuden URL www.avxcorp.com www.kemet.com www.murata.com www.tyuden.com
Setting the Output Voltage The output voltage is programmed using one feedback resistor according to the following formula:
V R1 = - OUT 10A
Inrush Current 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.
VOUT
6
U
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. While the internal diode is designed to handle such events, the inrush current should not be allowed to exceed 1.5A. For circuits that use flying capacitors within the recommended 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 current should be measured to ensure operation within the limits of the device. 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 capacitor switches directions within a cycle. Always use a ground plane under the switching regulator to minimize interplane coupling.
Suggested Layout (SOT-23) for Inverting Charge Pump
W
UU
+
GND CIN L1 CFLY VIN 1 2 3 COUT R1 SHDN 6 5 4
3483 AI01
3483f
LT3483
TYPICAL APPLICATIO
3.6V to -8V DC/DC Converter Low Profile, Small Footprint
L1 10H C2 0.22F
VIN 3.6V
SW VIN C1 4.7F LT3483 SHDN FB GND D 5pF R1 806k
C1: MURATA GRM219R61A475KE34B C2: TAIYO YUDEN LMK107BJ224 C3: MURATA GRM219R61C225KA88B D1: PHILIPS PMEG2005EB L1: MURATA LQH2MCN100K02L
PACKAGE DESCRIPTIO
0.62 MAX
0.95 REF
3.85 MAX 2.62 REF
RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR
0.20 BSC 1.00 MAX DATUM `A'
0.30 - 0.50 REF
NOTE: 1. DIMENSIONS ARE IN MILLIMETERS 2. DRAWING NOT TO SCALE 3. DIMENSIONS ARE INCLUSIVE OF PLATING
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.
U
U
Switching Waveform
D1 10 VOUT 20mV/DIV VOUT -8V 25mA C3 2.2F ISW 100mA/DIV 2s/DIV
3483 TA04a 3483 TA04b
S6 Package 6-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1636)
2.90 BSC (NOTE 4)
1.22 REF
1.4 MIN
2.80 BSC
1.50 - 1.75 (NOTE 4) PIN ONE ID
0.95 BSC
0.30 - 0.45 6 PLCS (NOTE 3)
0.80 - 0.90 0.01 - 0.10
0.09 - 0.20 (NOTE 3)
1.90 BSC
S6 TSOT-23 0302
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
3483f
7
LT3483
TYPICAL APPLICATIO S
3.6V to -22V DC/DC Converter
L1 10H C2 0.1F D1 RS 30 D 5pF R1 2.2M C3 1F
VIN 3.6V
VIN C1 4.7F LT3483
EFFICIENCY (%)
SW
SHDN FB GND
C1: TAIYO YUDEN LMK316BJ475MD C2: TAIYO YUDEN TMK107BJ104 (X5R) C3: TAIYO YUDEN TMK316BJ105MD D1: PHILIPS PMEG3002AEB L1: MURATA LQH2MCN100K02L
-5V DC/DC Converter
L1A 10H VIN 1nF 10 L1B 10H
*
SW VIN D
*
70
EFFICIENCY (%)
VOUT -5V 22pF 511k C2 10F
C1 4.7F
LT3483 SHDN FB GND
C1: TAIYO YUDEN EMK316BJ475ML C2: TAIYO YUDEN JMK316BJ106ML L1A, L1B: WURTH 744876100
RELATED PARTS
PART NUMBER LT1617/LT1617-1 LT1931/LT1931A LT1945 LT3463 DESCRIPTION 350mA/100mA (ISW) High Efficiency Micropower Inverting DC/DC Converter 1A (ISW), 1.2MHz/2.2MHz, High Efficiency Micropower Inverting DC/DC Converter Dual Output, Boost/Inverter, 350mA (ISW), Constant Off-Time, High Efficiency Step-Up DC/DC Converter Dual Output, Boost/Inverter, 250mA (ISW), Constant Off-Time, High Efficiency Step-Up DC/DC Converter with Integrated Schottky Diodes 85mA (ISW), High Efficiency Step-Up DC/DC Converter with Integrated Schottky and PNP Disconnect Boost (350mA) and Inverting (400mA) DC/DC Converter for CCD Bias with Integrated Schottkys COMMENTS VIN: 1.2V to 15V, VOUT(MAX) = -34V, IQ = 20A, ISD < 1A ThinSOT Package VIN: 2.6V to 16V, VOUT(MAX) = -34V, IQ = 5.8mA, ISD < 1A ThinSOT Package VIN: 1.2V to 15V, VOUT(MAX) = 34V, IQ = 40A, ISD < 1A, MS10 Package VIN: 2.3V to 15V, VOUT(MAX) = 40V, IQ = 40A, ISD < 1A DFN Package VIN: 2.3V to 10V, VOUT(MAX) = 34V, IQ = 25A, ISD < 1A ThinSOT Package VIN: 2.3V to 15V, VOUT(MAX) = 40V, IQ = 2.8mA, ISD < 1A DFN Package
3483f
LT3464 LT3472
8
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 FAX: (408) 434-0507
U
3.6V to -22V Converter Efficiency and Power Loss
75 EFFICIENCY 70
VOUT -22V 8mA
1000
100 POWER LOSS (mW)
65 POWER LOSS 60
10
1
3483 TA02a
55 0.1
1 LOAD CURRENT (mA)
0.1 10
3483 TA02b
- 5V Efficiency
75
VIN = 5V 65 VIN = 12V 60
3483 TA03a
55 0.1 1 10 LOAD CURRENT (mA) 100
3483 TA03b
LT/TP 1004 1K * PRINTED IN THE USA
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2004

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