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LT3463/LT3463A Dual Micropower DC/DC Converters with Schottky Diodes
FEATURES
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DESCRIPTIO
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Generates Well-Regulated Positive and Negative Outputs Low Quiescent Current: 20A (per Converter) in Active Mode <1A in Shutdown Mode Internal 42V Power Switches Internal 42V Schottky Diodes Low VCESAT Switch: 180mV at 150mA Input Voltage Range: 2.4V to 15V High Output Voltages: Up to 40V Low Profile (0.8mm) 3mm x 3mm DFN Package
APPLICATIO S
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CCD Bias LCD Bias Handheld Computers Digital Cameras
The LT(R)3463/LT3463A are dual micropower DC/DC converters with internal Schottky diodes in a 10-lead 3mm x 3mm DFN package. Negative and positive LT3463 converters have a 250mA current limit. The LT3463A positive converter also has a 250mA limit, while the negative converter has a 400mA limit. Both devices have an input voltage range of 2.4V to 15V, making them ideal for a wide variety of applications. Each converter features a quiescent current of only 20A, which drops to under 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. The 42V switch enables high voltage outputs up to 40V to be easily generated without the use of costly transformers. The low 300ns offtime 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 APPLICATIO
VIN 2.7V TO 5V 4.7F VIN SHDN1 LT3463A SHDN2 GND SW2 SW1 VOUT1 FB1 VREF FB2 D2 10H
CCD Bias Supply (15V, -8V)
VOUT1 15V 10mA 2.2F
EFFICIENCY (%)
Efficiency and Power Loss
80 15V EFFICIENCY 75 70 65 60 15V LOSS 55 40 -8V LOSS 0 100
3463 TA01b
1M
90.9k
154k
10H
1F
1M
10pF VOUT2 -8V 50mA
3463 TA01a
50 0.1 1 10 LOAD CURRENT (mA)
4.7F
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VIN = 3.6V 240 200
POWER LOSS (mW)
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-8V EFFICIENCY
160 120 80
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LT3463/LT3463A
ABSOLUTE
(Note 1)
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PACKAGE/ORDER I FOR ATIO
TOP VIEW VOUT1 SW1 VIN SW2 D2 1 2 3 4 5 11 10 FB1 9 SHDN1 8 SHDN2 7 VREF 6 FB2
VIN, SHDN1, SHDN2 Voltage ................................... 15V SW1, SW2, VOUT1 Voltage ....................................... 42V D2 Voltage ............................................................. -42V FB1, FB2 Voltage Range .............................. -0.3V to 2V Junction Temperature ........................................... 125C Operating Ambient Temperature Range (Note 2) .............................................. - 40C to 85C Storage Temperature Range ................. - 65C to 125C
ORDER PART NUMBER LT3463EDD LT3463AEDD DD PART MARKING LAFC LBJK
DD PACKAGE 10-LEAD (3mm x 3mm) PLASTIC DFN TJMAX = 125C, JA = 43C/W, JC = 3C/W EXPOSED PAD (PIN 11) IS GND AND MUST BE SOLDERED TO PCB
Consult LTC Marketing for parts specified with wider operating temperature ranges.
The q denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = 2.5V, VSHDN = 2.5V unless otherwise noted.
PARAMETER Minimum Input Voltage Total Quiescent Current Shutdown Current VREF Pin Voltage VREF Pin Voltage Line Regulation FB1 Comparator Trip Voltage FB1 Comparator Hysteresis FB1 Line Regulation FB1 Pin Bias Current (Note 3) FB2 Comparator Trip Voltage FB2 Comparator Hysteresis FB2 Line Regulation (VREF - VFB2) FB2 Pin Bias Current (Note 4) SW1 Switch Off Time SW2 Switch Off Time Switch VCESAT (SW1, SW2) Switch Current Limit (SW1) Switch Current Limit (SW2) Swith Leakage Current (SW1, SW2) Schottky Forward Voltage (VOUT1, D2) Schottky Reverse Leakage Current SHDN1 Pin Current SHDN2 Pin Current SHDN1/SHDN2 Start-Up Threshold CONDITIONS For Both Switchers, Not Switching VSHDN1 = VSHDN2 = 0V With 124k to GND With 124k to GND High to Low Transition 2.5V < VIN < 15V VFB1 = 1.3V Low to High Transition 2.5V < VIN < 15V VFB2 = -0.1V VOUT1 - VIN = 4V VOUT1 - VIN = 0V VFB2 < 0.1V VFB2 = 1V ISW = 150mA LT3463 LT3463A Switch Off, VSW = 42V ID = 150mA VOUT1 - VSW = 42V VD2 = -42V VSHDN1 = 2.5V VSHDN2 = 2.5V MIN TYP 2.2 40 0.1 1.25 0.05 1.25 8 0.05 20 3 8 0.05 20 300 1.5 300 1.5 180 250 250 400 0.01 750 1 1 4 4 1 MAX 2.4 60 1 1.27 0.10 1.275 0.10 50 12 0.10 50 UNITS V A A V %/V V mV %/V nA mV mV %/V nA ns s ns s mV mA mA mA A mV A A A A V
ELECTRICAL CHARACTERISTICS
q q
1.23 1.225
q q
0
q
180 180 320
320 320 460 1 5 5 10 10 1.5
0.3
Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: The LT3463/LT3463A are guaranteed to meet performance specifications from 0C to 70C. Specifications over the -40C to 85C
operating ambient temperature range are assured by design, characterization and correlation with statistical process controls. Note 3: Bias current flows into the FB1 pin. Note 4: Bias current flows out of the FB2 pin.
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LT3463/LT3463A TYPICAL PERFOR A CE CHARACTERISTICS
VCESAT and VDIODE Voltage
900 800 VCESAT AND VDIODE VOLTAGE (V) 700 600 500 400 300 200 100 ISWITCH = 150mA 0 25 50 75 100 125 FOR BOTH SWITCHERS IDIODE = 150mA
VREF AND VFB1 VOLTAGE (V)
1.25 VFB1
VREF
VFB2 VOLTAGE (mV)
0 -50 -25
TEMPERATURE (C)
3463 G01
Switch Off Time
400 350 450 400
SWITCH CURRENT LIMIT (mA)
SWITCH OFF TIME (ns)
300 250 200 150 100 50 0 -50 -25 0 25 50 75 100 125
300 250 200 150 100 50 0 -50 -25 0 25 50 75 100 125 LT3463 SW1, SW2 LT3463A SW1
QUIESCENT CURRENT (A)
TEMPERATURE (C)
3463 G04
PI FU CTIO S
VOUT1 (Pin 1): Output Voltage Switcher 1. This is the cathode of an internal Schottky diode whose anode is connected to the SW1 pin. SW1 (Pin 2): Switch Pin for Switcher 1. This is the collector of the internal NPN switch. Minimize the metal trace area connected to this pin to minimize EMI. VIN (Pin 3): Input Supply Pin. Bypass this pin with a capacitor as close to the device as possible. SW2 (Pin 4): Switch Pin for Switcher 2. This is the collector of the internal NPN switch. Minimize the metal trace area connected to this pin to minimize EMI. D2 (Pin 5): Diode for Switcher 2. This is the anode of an internal Schottky diode whose cathode connected to the GND pin. FB2 (Pin 6): Feedback Pin for Switcher 2. Set the output voltage by selecting values for R3 and R4. VREF (Pin 7): Voltage Reference Pin (1.25V). This pin is used along with FB2 to set the negative output voltage for Switcher 2. SHDN2 (Pin 8): Shutdown Pin for Switcher 2. Pull this pin above 1.5V to enable Switcher 2. Pull below 0.3V to turn it off. Do not leave this pin floating.
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VREF and VFB1 Voltage
1.27 10
VFB2 Voltage
1.26
8
6
1.24
4
1.23
2
1.22 -50 -25
0
25
50
75
100
125
0 -50 -25
TEMPERATURE (C)
3463 G02
50 25 75 0 TEMPERATURE (C)
100
125
3463 G03
Switch Current Limit
60
Quiescent Current
LT3463A SW2 350
50 40 30 20 10 NOT SWITCHING VFB1 = 1.3V VFB2 = -0.1V 50 25 75 0 TEMPERATURE (C) 100 125
0 -50 -25
TEMPERATURE (C)
3463 G05
3463 G06
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LT3463/LT3463A
PI FU CTIO S
SHDN1 (Pin 9): Shutdown Pin for Switcher 1. Pull this pin above 1.5V to enable Switcher 1. Pull below 0.3V to turn it off. Do not leave this pin floating. FB1 (Pin 10): Feedback Pin for Switcher 1. Set the output voltage by selecting values for R1 and R2. GND (Pin 11): Exposed Pad. Solder this exposed pad directly to the local ground plane. This pad must be electrically connected for proper operation.
BLOCK DIAGRA
VIN C1
3 VIN SHDN1 9 SHDN1
VOUT1 R2 10 R1 1.25V FB1
- +
A1 SWITCHER 1 A2
LT3463: RS1 = RS2 = 0.1 LT3463A: RS1 = 0.1, RS2 = 0.063
OPERATIO
The LT3463 uses a constant off-time control scheme to provide high efficiency over a wide range of output current. Operation can be best understood by referring to the block diagram in Figure 1. When the voltage at the FB1 pin is slightly above 1.25V, comparator A1 disables most of the internal circuitry. Output current is then provided by capacitor C2, which slowly discharges until the voltage at the FB1 pin goes below the hysteresis point of A1 (typical hysteresis at the FB1 pin is 8mV). A1 then enables the internal circuitry, turns on power switch Q1, and the
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L1
VOUT1
VOUT2
D3
C4
L2 VIN
C2
C3
2 SW1
1 VOUT1 D1
5 D2 D2
4 SW2 SHDN2 8 SHDN2
300ns ONE-SHOT
Q1
Q2
300ns ONE-SHOT
1.25V
VREF
7 R3
+
RS1 RS2 25mV
+
25mV
+ -
FB2
6 R4
-
-
A4 SWITCHER 2
A3
VOUT2
GND 11
3463 F01
Figure 1. Block Diagram
current in inductor L1 begins ramping up. Once the switch current reaches 250mA, comparator A2 resets the oneshot, which turns off Q1 for 300ns. Q1 turns on again and the inductor currents ramp back up to 250mA, then A2 again resets the one-shot. This switching action continues until the output voltage is charged up (until the FB1 pin reaches 1.25V), then A1 turns off the internal circuitry and the cycle repeats. The second switching regulator is an inverting converter (which generates a negative output) but the basic operation is the same.
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LT3463/LT3463A
APPLICATIO S I FOR ATIO
Choosing an Inductor
Several recommended inductors that work well with the LT3463 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 CMD4D06 MAX MAX HEIGHT L (H) IDC (mA) DCR() (mm) MANUFACTURER 4.7 750 0.22 0.8 Sumida 10 500 0.46 (847) 956-0666 22 310 1.07 www.sumida.com 10 500 0.19 1.8 Sumida 22 310 0.36 4.7 600 0.16 1.2 Coilcraft 10 400 0.30 (847) 639-6400 22 280 0.64 www.coilcraft.com 10 450 0.39 1.8 Murata 15 300 0.75 (714) 852-2001 22 250 0.92 www.murata.com 4.7 340 0.85 1.8 Murata
CDRH3D16 LPO4812
LQH32C
LQH31C
Inductor Selection--Boost Regulator The formula below calculates the appropriate inductor value to be used for a boost regulator using the LT3463 (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 = 0.5V (Schottky diode voltage), ILIM = 250mA (or 400mA) and tOFF = 300ns; for designs with varying VIN
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such as battery powered applications, use the minimum VIN value in the above equation. For most regulators with output voltages below 7V, a 4.7H inductor is the best choice, even though the equation above might specify a smaller value. For higher output voltages, the formula above will give large inductance values. For a 3V 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 much reduction in the maximum output current. Inductor Selection--Inverting Regulator The formula below calculates the appropriate inductor value to be used for an inverting regulator using the LT3463 (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:
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VOUT + VD L = 2 ILIM
tOFF
where VD = 0.5V (Schottky diode voltage), ILIM = 250mA (or 400mA) and tOFF = 300ns. For higher output voltages, the formula above will give large inductance values. For a 3V to 20V converter (typical LCD bias application), a 49H inductor is called for with the above equation, but a 10H or 22H inductor could be used without much reduction in the 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
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LT3463/LT3463A
APPLICATIO S I FOR ATIO
output voltages from a high input voltage source will often exceed the 50V maximum switch rating. For instance, a 12V to - 40V converter using the inverting topology would generate 52V on the SW pin, exceeding its maximum rating. For this application, 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 LT3463. 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
Capacitor Selection The small size and low ESR of ceramic capacitors makes them ideal for LT3463 applications. Use only X5R and X7R types because they retain their capacitance over wider voltage and temperature ranges than other ceramic types. A 1F input capacitor and a 0.22F or 0.47F output capacitor are sufficient for most applications. Table 2 shows a list of several ceramic capacitor manufacturers. Consult the manufacturers for more detailed information on their entire selection of ceramic capacitors. For applications needing very low output voltage ripple, larger output capacitor values can be used.
Table 2. Recommended Ceramic Capacitor Manufacturers
MANUFACTURER AVX Kemet Murata Taiyo Yuden PHONE 843-448-9411 408-986-0424 814-237-1431 408-573-4150 URL www.avxcorp.com www.kemet.com www.murata.com www.t-yuden.com
Inrush Current When VIN is increased from ground to operating voltage while the output capacitor is discharged, an inrush current will flow through the inductor and integrated Schottky diode into the output capacitor. Conditions that increase
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inrush current include a larger more abrupt voltage step at VIN, a larger output capacitor tied to the outputs, 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 amp. For circuits that use output capacitor values within the recommended range and have input voltages of less than 5V, inrush current remains low, posing no hazard to the device. In cases where there are large steps at VIN and/or a large capacitor is used at the outputs, inrush current should be measured to ensure safe operation. Setting the Output Voltages The output voltages are programmed using two feedback resistors. As shown in Figure 1, resistors R1 and R2 program the positive output voltage (for Switcher 1), and resistors R3 and R4 program the negative output voltage (for Switcher 2) according to the following formulas:
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R2 VOUT 1 = 1.25V 1 + R1 R4 VOUT 2 = -1.25V R3
R1 and R3 are typically 1% resistors with values in the range of 50k to 250k. Board Layout Considerations As with all switching regulators, careful attention must be paid to the PCB board layout and component placement. To maximize efficiency, switch rise and fall times are made as short as possible. To prevent electromagnetic interference (EMI) problems, proper layout of the high frequency switching path is essential. The voltage signal of the SW pin has sharp rising and falling edges. Minimize the length and area of all traces connected to the SW pin and always use a ground plane under the switching regulator to minimize interplane coupling. In addition, the ground connection for the feedback resistor R1 should be tied directly to the GND pin and not shared with any other component, ensuring a clean, noise-free connection.
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LT3463/LT3463A
TYPICAL APPLICATIO
VIN 2.7V TO 5V
PACKAGE DESCRIPTIO
0.675 0.05
3.50 0.05 1.65 0.05 2.15 0.05 (2 SIDES) PACKAGE OUTLINE 0.25 0.05 0.50 BSC 2.38 0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS NOTE: 1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-2). CHECK THE LTC WEBSITE DATA SHEET FOR CURRENT STATUS OF VARIATION ASSIGNMENT 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE PIN 1 TOP MARK (SEE NOTE 6)
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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Dual Output 20V Converter
L1 10H C1 1F R2 1M R1 66.5k VOUT1 20V 9mA C2 0.47F 3 VIN 9 SHDN1 LT3463 8 SHDN2 GND 11 L2 10H SW2 4 C4 0.1F 2 1 10 7 6 R3 61.9k SW1 VOUT1 FB1 VREF FB2 D2 5 D1 C3 0.47F R4 1M VOUT2 -20V 9mA
3463 TA02
DD Package 10-Lead Plastic DFN (3mm x 3mm)
(Reference LTC DWG # 05-08-1699)
R = 0.115 TYP 6 0.38 0.10 10
3.00 0.10 (4 SIDES)
1.65 0.10 (2 SIDES)
(DD10) DFN 1103
5 0.200 REF 0.75 0.05 2.38 0.10 (2 SIDES)
1
0.25 0.05 0.50 BSC
0.00 - 0.05
BOTTOM VIEW--EXPOSED PAD
5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE
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LT3463/LT3463A
TYPICAL APPLICATIO
VIN 2.7V TO 5V
Typical Waveforms for 15V Output
VSW1 10V/DIV VOUT1 AC-COUPLED 50mV/DIV IL1 200mA/DIV 2s/DIV
RELATED PARTS
PART NUMBER DESCRIPTION COMMENTS VIN: 1V to 15V, VOUT(MAX): 34V, IQ: 20A, ISD: <1A, ThinSOT Package VIN: 1.2V to 15V, VOUT(MAX): 34V, IQ: 20A, ISD: <1A, MS Package VIN: 1.2V to 15V, VOUT(MAX): 34V, IQ: 20A, ISD: <1A, MS Package VIN: 1.2V to 15V, VOUT(MAX): 34V, IQ: 20A, ISD: <1A, MS Package VIN: 2.3V to 10V, VOUT(MAX): 34V, IQ: 25A, ISD: <1A, ThinSOT Package LT1615/LT1615-1 300mA/80mA (ISW), High Efficiency Step-Up DC/DC Converters LT1944 LT1944-1 LT1945 LT3464 Dual Output 350mA (ISW), Constant Off-Time, High Efficiency Step-Up DC/DC Converter Dual Output 150mA (ISW), Constant Off-Time, High Efficiency Step-Up DC/DC Converter Dual Output, Pos/Neg, 350mA (ISW), Constant Off-Time, High Efficiency Step-Up DC/DC Converter 85mA (ISW), High Efficiency Step-Up DC/DC Converter with Integrated Schottky and PNP Disconnect
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Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 q FAX: (408) 434-0507
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CCD Bias Supply
L1 10H C1 4.7F 9 R2 1M R1 90.9k VOUT1 15V 10mA C2 2.2F 3 VIN SHDN1 LT3463A 8 SHDN2 GND 11 L2 10H SW2 4 C4 1F 2 1 10 7 6 R3 154k SW1 VOUT1 FB1 VREF FB2 D2 5 D1 R4 1M C3 4.7F C5 10pF VOUT2 -8V 50mA
3463 TA01a
C1: TAIYO YUDEN JMK212BJ475MG C2: TAIYO YUDEN EMK316BJ225ML C3: TAIYO YUDEN LMK316BJ475ML C4: TAIYO YUDEN EMK212BJ105MG C5: AVX 06035A100KAT2A D1: DIODES, INC B0540W L1, L2: MURATA LQH32CN100K53
Typical Waveforms for -8V Output
VSW2 5V/DIV VOUT2 AC-COUPLED 50mV/DIV IL2 200mA/DIV
3463 TA04
2s/DIV
3463 TA05
3463f LT/TP 0404 1K * PRINTED IN USA
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2003

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