LT3463/LT3463A Dual Micropower DC/DC Converters with Schottky Diodes U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO The LT®3463/LT3463A are dual micropower DC/DC converters with internal Schottky diodes in a 10-lead 3mm × 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 20µA, which drops to under 1µA 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. Generates Well-Regulated Positive and Negative Outputs Low Quiescent Current: 20µA (per Converter) in Active Mode <1µA 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 U APPLICATIO S ■ ■ ■ ■ CCD Bias LCD Bias Handheld Computers Digital Cameras , LTC and LT are registered trademarks of Linear Technology Corporation. U TYPICAL APPLICATIO CCD Bias Supply (15V, –8V) Efficiency and Power Loss 10µH VIN 2.7V TO 5V 1M SW1 VOUT1 SHDN2 GND 90.9k VREF FB2 SW2 15V EFFICIENCY 200 2.2µF FB1 LT3463A 154k 70 160 –8V EFFICIENCY 65 120 60 80 D2 15V LOSS 55 10µH 1µF 240 POWER LOSS (mW) VIN SHDN1 VIN = 3.6V 75 EFFICIENCY (%) 4.7µF 80 VOUT1 15V 10mA 1M 4.7µF 40 –8V LOSS 10pF VOUT2 –8V 50mA 50 0.1 1 10 LOAD CURRENT (mA) 0 100 3463 TA01b 3463 TA01a 3463f 1 LT3463/LT3463A U W W W ABSOLUTE AXI U RATI GS U W U PACKAGE/ORDER I FOR ATIO (Note 1) VIN, SHDN1, SHDN2 Voltage ................................... 15V SW1, SW2, VOUT1 Voltage ....................................... 42V D2 Voltage ............................................................. –42V FB1, FB2 Voltage Range .............................. –0.3V to 2V Junction Temperature ........................................... 125°C Operating Ambient Temperature Range (Note 2) .............................................. – 40°C to 85°C Storage Temperature Range ................. – 65°C to 125°C TOP VIEW ORDER PART NUMBER 10 FB1 VOUT1 1 SW1 2 VIN 3 SW2 4 7 VREF D2 5 6 FB2 9 SHDN1 11 8 SHDN2 DD PACKAGE 10-LEAD (3mm × 3mm) PLASTIC DFN TJMAX = 125°C, θJA = 43°C/W, θJC = 3°C/W EXPOSED PAD (PIN 11) IS GND AND MUST BE SOLDERED TO PCB LT3463EDD LT3463AEDD DD PART MARKING LAFC LBJK 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 = 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 MIN For Both Switchers, Not Switching VSHDN1 = VSHDN2 = 0V With 124kΩ to GND With 124kΩ to GND High to Low Transition ● 1.23 ● 1.225 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 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 0°C to 70°C. Specifications over the –40°C to 85°C ● 0 ● 180 180 320 0.3 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 50 320 320 460 1 5 5 10 10 1.5 UNITS V µA µA V %/V V mV %/V nA mV mV %/V nA ns µs ns µs mV mA mA mA µA mV µA µA µA µA V 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. 3463f 2 LT3463/LT3463A U W TYPICAL PERFOR A CE CHARACTERISTICS VCESAT and VDIODE Voltage 900 VREF and VFB1 Voltage FOR BOTH SWITCHERS VFB2 Voltage 1.27 10 1.26 8 600 VREF 1.25 500 400 VFB1 1.24 300 200 6 4 2 1.23 ISWITCH = 150mA 0 –50 –25 0 25 50 75 100 1.22 –50 –25 125 TEMPERATURE (°C) 0 25 50 75 100 TEMPERATURE (°C) Switch Off Time 450 350 400 SWITCH CURRENT LIMIT (mA) 400 250 200 150 100 50 60 50 LT3463A SW2 300 250 LT3463 SW1, SW2 LT3463A SW1 150 100 25 50 75 100 125 TEMPERATURE (°C) 0 –50 –25 40 30 20 10 50 0 125 Quiescent Current 350 200 100 3463 G03 Switch Current Limit 300 50 25 75 0 TEMPERATURE (°C) 3463 G02 3463 G01 0 –50 –25 0 –50 –25 125 QUIESCENT CURRENT (µA) 100 SWITCH OFF TIME (ns) VFB2 VOLTAGE (mV) IDIODE = 150mA 700 VREF AND VFB1 VOLTAGE (V) VCESAT AND VDIODE VOLTAGE (V) 800 0 25 50 75 100 125 TEMPERATURE (°C) 3463 G04 3463 G05 NOT SWITCHING VFB1 = 1.3V VFB2 = –0.1V 0 –50 –25 50 25 75 0 TEMPERATURE (°C) 100 125 3463 G06 U U U 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. D2 (Pin 5): Diode for Switcher 2. This is the anode of an internal Schottky diode whose cathode connected to the GND 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. FB2 (Pin 6): Feedback Pin for Switcher 2. Set the output voltage by selecting values for R3 and R4. VIN (Pin 3): Input Supply Pin. Bypass this pin with a capacitor as close to the device as possible. VREF (Pin 7): Voltage Reference Pin (1.25V). This pin is used along with FB2 to set the negative output voltage for Switcher 2. 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. 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. 3463f 3 LT3463/LT3463A U U U 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. GND (Pin 11): Exposed Pad. Solder this exposed pad directly to the local ground plane. This pad must be electrically connected for proper operation. FB1 (Pin 10): Feedback Pin for Switcher 1. Set the output voltage by selecting values for R1 and R2. W BLOCK DIAGRA VOUT1 L1 VOUT2 C4 D3 L2 VIN VIN C2 C1 3 2 VIN 9 SHDN1 C3 1 5 VOUT1 SW1 300ns ONE-SHOT VOUT1 SW2 D2 D1 SHDN1 4 D2 SHDN2 8 300ns ONE-SHOT Q2 Q1 1.25V VREF SHDN2 7 R3 R2 10 FB1 RS1 1.25V + A1 A2 – + + + – R1 FB2 6 R4 RS2 25mV 25mV SWITCHER 1 – A4 A3 – VOUT2 SWITCHER 2 GND 11 3463 F01 LT3463: RS1 = RS2 = 0.1Ω LT3463A: RS1 = 0.1Ω, RS2 = 0.063Ω Figure 1. Block Diagram U 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 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. 3463f 4 LT3463/LT3463A U U W U 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 CDRH3D16 LPO4812 LQH32C LQH31C MAX MAX HEIGHT L (µH) IDC (mA) DCR(Ω) (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 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 such as battery powered applications, use the minimum VIN value in the above equation. For most regulators with output voltages below 7V, a 4.7µH 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 21µH inductor is called for with the above equation, but a 10µH 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: 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 49µH inductor is called for with the above equation, but a 10µH or 22µH 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 3463f 5 LT3463/LT3463A U U W U 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 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 1µF input capacitor and a 0.22µF or 0.47µF 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 AVX PHONE 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: tOFF Capacitor Selection MANUFACTURER 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. URL 843-448-9411 www.avxcorp.com Kemet 408-986-0424 www.kemet.com Murata 814-237-1431 www.murata.com Taiyo Yuden 408-573-4150 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 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. 3463f 6 LT3463/LT3463A U TYPICAL APPLICATIO Dual Output ±20V Converter VIN 2.7V TO 5V L1 10µH C1 1µF 3 2 9 SHDN1 FB1 LT3463 8 SHDN2 GND R2 1M 1 SW1 VOUT1 VIN VREF FB2 SW2 D2 4 5 11 C4 0.1µF L2 10µH VOUT1 20V 9mA R1 66.5k 10 C2 0.47µF 7 6 R3 61.9k R4 1M D1 VOUT2 –20V 9mA C3 0.47µF 3463 TA02 U PACKAGE DESCRIPTIO DD Package 10-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1699) R = 0.115 TYP 6 0.38 ± 0.10 10 0.675 ±0.05 3.50 ±0.05 1.65 ±0.05 2.15 ±0.05 (2 SIDES) 3.00 ±0.10 (4 SIDES) PACKAGE OUTLINE 1.65 ± 0.10 (2 SIDES) PIN 1 TOP MARK (SEE NOTE 6) (DD10) DFN 1103 5 0.25 ± 0.05 0.200 REF 0.50 BSC 2.38 ±0.05 (2 SIDES) 1 0.75 ±0.05 0.00 – 0.05 0.25 ± 0.05 0.50 BSC 2.38 ±0.10 (2 SIDES) BOTTOM VIEW—EXPOSED PAD 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 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 3463f 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 LT3463/LT3463A U TYPICAL APPLICATIO CCD Bias Supply VIN 2.7V TO 5V L1 10µH C1 4.7µF 3 VIN 9 2 FB1 LT3463A 8 SHDN2 GND 11 R2 1M 1 SW1 VOUT1 SHDN1 VREF FB2 SW2 10 R1 90.9k C2 2.2µF 7 6 R3 154k D2 4 L2 10µH VOUT1 15V 10mA 5 C4 1µF D1 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 15V Output C5 10pF R4 1M C3 4.7µF VOUT2 –8V 50mA 3463 TA01a Typical Waveforms for –8V Output VSW2 5V/DIV VSW1 10V/DIV VOUT1 AC-COUPLED 50mV/DIV VOUT2 AC-COUPLED 50mV/DIV IL1 200mA/DIV IL2 200mA/DIV 2µs/DIV 3463 TA04 2µs/DIV 3463 TA05 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1615/LT1615-1 300mA/80mA (ISW), High Efficiency Step-Up DC/DC Converters VIN: 1V to 15V, VOUT(MAX): 34V, IQ: 20µA, ISD: <1µA, ThinSOT Package LT1944 Dual Output 350mA (ISW), Constant Off-Time, High Efficiency Step-Up DC/DC Converter VIN: 1.2V to 15V, VOUT(MAX): 34V, IQ: 20µA, ISD: <1µA, MS Package LT1944-1 Dual Output 150mA (ISW), Constant Off-Time, High Efficiency Step-Up DC/DC Converter VIN: 1.2V to 15V, VOUT(MAX): 34V, IQ: 20µA, ISD: <1µA, MS Package LT1945 Dual Output, Pos/Neg, 350mA (ISW), Constant Off-Time, High Efficiency Step-Up DC/DC Converter VIN: 1.2V to 15V, VOUT(MAX): ±34V, IQ: 20µA, ISD: <1µA, MS Package LT3464 85mA (ISW), High Efficiency Step-Up DC/DC Converter with Integrated Schottky and PNP Disconnect VIN: 2.3V to 10V, VOUT(MAX): 34V, IQ: 25µA, ISD: <1µA, ThinSOT Package 3463f 8 Linear Technology Corporation LT/TP 0404 1K • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com LINEAR TECHNOLOGY CORPORATION 2003