LT1946A 2.7MHz Boost DC/DC Converter with 1.5A Switch and Soft-Start U FEATURES ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO 1.5A, 36V Internal Switch 2.7MHz Switching Frequency Integrated Soft-Start Function Adjustable Output from VIN to 35V Low VCESAT Switch: 300mV at 1.5A (Typical) 12V at 430mA from a 5V Input Small Thermally Enhanced 8-Lead MSOP Package U APPLICATIO S ■ ■ ■ ■ TFT-LCD Bias Supplies GPS Receivers DSL Modems Local Power Supply The LT®1946A is a fixed frequency step-up DC/DC converter containing an internal 1.5A, 36V switch. Capable of generating 12V at 430mA from a 5V input, the LT1946A is ideal for powering large TFT-LCD panels. The LT1946A switches at 2.7MHz, allowing the use of tiny, low profile inductors and low value ceramic capacitors. Loop compensation can be either internal or external, giving the user flexibility in setting loop compensation and allowing optimized transient response with low ESR ceramic output capacitors. Soft-start is controlled with an external capacitor which determines the input current ramp rate during start up. The 8-lead MSOP package and high switching frequency ensure a low profile overall solution less than 1.1mm high. , LTC and LT are registered trademarks of Linear Technology Corporation. U TYPICAL APPLICATIO L1 2.2µH VIN 5V 6 C1 2.2µF 3 1 RC 27.4k CC 270pF VIN 90 R1 182k 85 SHDN 80 2 LT1946A FB 7 COMP VC SS CSS 100nF 5 SW Efficiency VOUT 12V 430mA 8 GND* 4 C2 2.2µF R2 21k EFFICIENCY (%) OFF ON D1 75 70 65 60 C1: 2.2µF, X5R or X7R, 6.3V C2: 2.2µF, X5R or X7R, 16V D1: MICROSEMI UPS120 OR EQUIVALENT L1: SUMIDA CR43-2R2 * EXPOSED PAD MUST ALSO BE GROUNDED 1946A TA01 Figure 1. 5V to 12V, 430mA Step-Up DC/DC Converter 55 50 0 100 200 300 400 LOAD CURRENT (mA) 500 1946A TA01 sn1946a 1946afs 1 LT1946A W W W AXI U U ABSOLUTE RATI GS U U W PACKAGE/ORDER I FOR ATIO (Note 1) VIN Voltage .............................................................. 16V SW Voltage ................................................– 0.4V to 36V FB Voltage .............................................................. 2.5V Current into FB Pin ............................................... ±1mA SHDN Voltage .......................................................... 16V Maximum Junction Temperature .......................... 125°C Operating Temperature Range (Note 2) ....................................... – 40°C to 85°C Storage Temperature Range ................. – 65°C to 150°C Lead Temperature (Soldering, 10 sec).................. 300°C ORDER PART NUMBER TOP VIEW VC FB SHDN GND 1 2 3 4 8 7 6 5 SS COMP VIN SW LT1946AEMS8E MS8E PART MARKING MS8E PACKAGE 8-LEAD PLASTIC MSOP EXPOSED PAD IS GROUND (MUST BE SOLDERED TO PCB) LTYZ TJMAX = 125°C, θJA = 40°C/W, θJC = 10°C/W 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 = 3V, VSHDN = VIN unless otherwise noted. (Note 2) PARAMETER CONDITIONS MIN Minimum Operating Voltage TYP MAX 2.45 2.6 V 16 V 1.25 1.27 1.27 V V 20 120 Maximum Operating Voltage Feedback Voltage ● FB Pin Bias Current VFB = 1.25V (Note 3) Error Amp Transconductance ∆I = 2µA 1.23 1.22 ● Error Amp Voltage Gain Quiescent Current VSHDN = 2.5V, Not Switching Quiescent Current in Shutdown VSHDN = 0V, VIN = 3V Reference Line Regulation 2.6V ≤ VIN ≤ 16V Switching Frequency ● Switching Frequency in Foldback 2.4 2.3 VFB = 0V Maximum Duty Cycle Switch Current Limit (Note 4) Switch VCESAT ISW = 1A Switch Leakage Current VSW = 5V Soft-Start Charging Current VSS = 0.5V SHDN Input Voltage High µmhos 300 V/V 3.6 5 mA 0 1 µA 0.01 0.05 %/V 2.7 3 3.1 MHz MHz 0.85 MHz ● 73 80 ● 1.5 2.1 3.1 A 240 340 mV 0.01 1 µA 4 6 µA 2.5 % 2.4 VSHDN = 3V VSHDN = 0V Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: The LT1946AE is guaranteed to meet performance specifications from 0°C to 70°C. Specifications over the –40°C to 85°C operating nA 40 V SHDN Input Voltage Low SHDN Pin Bias Current UNITS 16 0 0.5 V 32 0.1 µA µA temperature range are assured by design, characterization and correlation with statistical process controls. Note 3: Current flows out of the FB pin. Note 4: Current limit guaranteed by design and/or correlation to static test. Current limit is independent of duty cycle and is guaranteed by design. sn1946a 1946afs 2 LT1946A U W TYPICAL PERFOR A CE CHARACTERISTICS Oscillator Frequency 3000 1.27 2700 1.26 1.25 1.24 1.23 1.22 1.21 2400 TA = –30°C 2100 TA = 100°C 1800 1500 TA = 25°C 1200 900 600 300 1.20 –50 –25 0 25 50 75 TEMPERATURE (°C) 100 0 125 0 0.2 0.4 0.6 0.8 FEEDBACK VOLTAGE (V) 1946A G01 1.2 –25 0 25 50 75 TEMPERATURE (°C) 100 125 1946A G03 Switching Waveforms for Figure 1 Circuit Quiescent Current 0.35 4.0 VOUT 100mV/DIV AC COUPLED 3.8 QUIESCENT CURRENT (mA) 0.30 0.25 VCESAT (V) 1 2.6 2.4 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 –50 1946A G02 Switch Saturation Voltage 0.20 0.15 0.10 0.05 0 Current Limit CURRENT LIMIT (A) 1.28 OSCILLATOR FREQUENCY (kHz) FEEDBACK VOLTAGE (V) Feedback Pin Voltage 3.6 VSW 10V/DIV 0V 3.4 3.2 3.0 ILI 0.5A/DIV 2.8 2.6 100ns/DIV 2.4 0 0.2 0.4 0.6 0.8 1 1.2 SWITCH CURRENT (A) 1.4 1.6 2.2 –50 1946A G04 –25 0 25 50 75 TEMPERATURE (°C) 100 125 1946A G05 Transient Response for Figure 1 Circuit Start-Up Waveforms for Figure 1 Circuit VOUT 100mV/DIV AC COUPLED VOUT 2V/DIV ILI 0.5A/DIV IIN 200mA/DIV 0A ILOAD 250mA 150mA VSHDN 5V 0V 50µs/DIV 1946A G06 1946A G07 RLOAD = 250Ω 1ms/DIV 1946A G08 sn1946a 1946afs 3 LT1946A U U U PI FU CTIO S VC (Pin 1): Error Amplifier Output Pin. Tie external compensation network to this pin or use the internal compensation network by shorting the VC pin to the COMP pin. External compensation consists of placing a resistor and capacitor in series from VC to GND. Typical capacitor range is from 90pF to 270pF. Typical resistor range is from 25k to 120k. FB (Pin 2): Feedback Pin. Reference voltage is 1.25V. Connect resistive divider tap here. Minimize trace area at FB. Set VOUT according to VOUT = 1.25 • (1+R1/R2). SHDN (Pin 3): Shutdown Pin. Tie to 2.4V or more to enable device. Ground to shut down. Do not float this pin. SW (Pin 5): Switch Pin. This is the collector of the internal NPN power switch. Minimize the metal trace area connected to this pin to minimize EMI. VIN (Pin 6): Input Supply Pin. Must be locally bypassed. COMP (Pin 7): Internal Compensation Pin. Provides an internal compensation network. Tie directly to the VC pin for internal compensation. Tie to GND if not used. SS (Pin 8): Soft-Start Pin. Place a soft-start capacitor here. Upon start-up, 4µA of current charges the capacitor to 1.5V. Use a larger capacitor for slower start-up. Leave floating if not in use. GND (Pin 4, Exposed Pad): Ground. Tie both Pin 4 and the exposed pad directly to local ground plane. The ground metal to the exposed pad should be wide for better heat dissipation. Multiple vias (local ground plane ↔ ground backplane) placed close to the exposed pad can further aid in reducing thermal resistance. sn1946a 1946afs 4 LT1946A W BLOCK DIAGRA SS VC COMP 8 1 7 4µA 120k 90pF – DRIVER A2 VIN 6 1.25V REFERENCE + + A1 FB 0.5V Q1 + 0.01Ω – + R2 (EXTERNAL) 4 GND A3 ÷3 2.7MHz OSCILLATOR – SHDN S Q RAMP GENERATOR R1 (EXTERNAL) SHUTDOWN R Σ – VOUT 5 SW COMPARATOR 3 2 EXPOSED PAD 1946A F02 FB Figure 2. Block Diagram sn1946a 1946afs 5 LT1946A U OPERATIO The LT1946A uses a constant frequency, current mode control scheme to provide excellent line and load regulation. Please refer to Figure 2 for the following description of the part’s operation. At the start of the oscillator cycle, the SR latch is set, turning on the power switch Q1. The switch current flows through the internal current sense resistor generating a voltage. This voltage is added to a stabilizing ramp and the resulting sum is fed into the positive terminal of the PWM comparator A2. When this voltage exceeds the level at the negative input of A2, the SR latch is reset, turning off the power switch. The level at the negative input of A2 (VC pin) is set by the error amplifier (A1) and is simply an amplified version of the difference between the feedback voltage and the reference voltage of 1.250V. In this manner, the error amplifier sets the correct peak current level to keep the output in regulation. Two functions are provided to enable a very clean start-up for the LT1946A. Frequency foldback is used to reduce the oscillator frequency by one-third when the FB pin is below a nominal value of 0.5V. This is accomplished via comparator A3. This feature reduces the minimum duty cycle that the part can achieve thus allowing better control of the switch current during start-up. When the FB pin voltage goes above 0.5V, the oscillator returns to the normal frequency of 2.7MHz. A soft-start function is also provided by the LT1946A. When the part is brought out of shutdown, 4µA of current is sourced out of the SS pin. By connecting an external capacitor to the SS pin, the rate of voltage rise on the pin can be set. Typical values for the soft-start capacitor range from 10nF to 200nF. The SS pin directly limits the rate of rise on the VC pin, which in turn limits the peak switch current. Current limit is not shown in Figure 2. The switch current is constantly monitored and not allowed to exceed the nominal value of 2.1A. If the switch current reaches 2.1A, the SR latch is reset regardless of the output of comparator A2. This current limit protects the power switch as well as various external components connected to the LT1946A. U W U U APPLICATIO S I FOR ATIO Inductor Selection Several inductors that work well with the LT1946A are listed in Table 1. This table is not complete, and 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, as many different sizes and shapes are available. Ferrite core inductors should be used to obtain the best efficiency, as core losses at 2.7MHz are much lower for ferrite cores than for the cheaper powdered-iron ones. Choose an inductor that can handle at least 1.5A without saturating, and ensure that the inductor has a low DCR (copper-wire resistance) to minimize I2R power losses. A 1.5µH to 4.7µH inductor will be the best choice for most LT1946A designs. Note that in some applications, the current handling requirements of the inductor can be lower, such as in the SEPIC topology where each inductor only carries one-half of the total switch current. The inductors shown in Table 1 were chosen for small size. For better efficiency, use similar valued inductors with a larger volume. Table 1. Recommended Inductors - LT1946A PART L (µH) MAX DCR (mΩ) Size LxWxH (mm) RLF5018-1R5M2R1 RLF5018-2R7M1R8 RLF5018-4R7M1R4 RLF5018-100MR94 1.5 2.7 4.7 10.0 25 33 45 67 5.2x5.6x1.8 TDK (847) 803-6100 www.tdk.com LPO1704-122MC LPO1704-222MC 1.2 2.2 80 120 5.5x6.6x1.0 Coilcraft (800) 322-2645 www.coilcraft.com CR43-2R2 CR43-3R3 2.2 3.3 71 86 4.5x4.0x3.2 Sumida (847) 956-0666 www.sumida.com VENDOR Capacitor Selection Low ESR (equivalent series resistance) capacitors should be used at the output to minimize the output ripple voltage. Multilayer ceramic capacitors are an excellent choice, as they have an extremely low ESR and are available in very small packages. X5R dielectrics are preferred, followed by X7R, as these materials retain the capacitance over wide voltage and temperature ranges. A 2.2µF to 20µF output sn1946a 1946afs 6 LT1946A U W U U APPLICATIO S I FOR ATIO capacitor is sufficient for most applications, but systems with very low output currents may need only a 1µF or smaller output capacitor. Solid tantalum or OSCON 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 LT1946A. A 2.2µF to 4.7µF input capacitor is sufficient for most applications. Table 2 shows a list of several ceramic capacitor manufacturers. Consult the manufacturers for detailed information on their entire selection of ceramic parts. Table 2. Ceramic Capacitor Manufacturers Taiyo Yuden (408) 573-4150 www.t-yuden.com AVX (803) 448-9411 www.avxcorp.com Murata (714) 852-2001 www.murata.com Compensation To compensate the feedback loop of the LT1946A, a series resistor-capacitor network should be connected from the COMP pin to GND. For most applications, a capacitor in the range of 90pF to 470pF will suffice. A good starting value for the compensation capacitor, CC, is 270pF. The compensation resistor, RC, is usually in the range of 20k to 100k. A good technique to compensate a new application is to use a 100k potentiometer in place of RC, and use a 270pF capacitor for CC. By adjusting the potentiometer while observing the transient response, the optimum value for RC can be found. Figures 3a-3c illustrate this process for the circuit of Figure 1. Figure 3a shows the transient response with RC equal to 2.5k. The phase margin is poor as evidenced by the excessive ringing in the output voltage and inductor current. In Figure 3b the value of RC is increased to 6.5k, which results in a more damped response. Figure 3c shows the results when RC is increased further to 27.4k. The transient response is nicely damped and the compensation procedure is complete. The COMP pin provides access to an internal resistor (120k) and capacitor (90pF). For some applications, these values will suffice and no external RC and CC will be needed. VOUT 200mV/DIV AC COUPLED IL1 0.5A/DIV RC = 2.5k 50µs/DIV 1946A F03a Figure 3a. Transient Response Shows Excessive Ringing VOUT 200mV/DIV AC COUPLED IL1 0.5A/DIV RC = 6.5k 50µs/DIV 1946A F03b Figure 3b. Transient Response is Better VOUT 200mV/DIV AC COUPLED IL1 0.5A/DIV RC = 27.4k 50µs/DIV 1946A F03c Figure 3c. Transient Response is Well Damped Compensation-Theory Like all other current mode switching regulators, the LT1946A needs to be compensated for stable and efficient operation. Two feedback loops are used in the LT1946A: a fast current loop which does not require compensation, and a slower voltage loop which does. Standard bode plot analysis can be used to understand and adjust the voltage feedback loop. sn1946a 1946afs 7 LT1946A U W U U APPLICATIO S I FOR ATIO 1 2 • π • ESR • C OUT As with any feedback loop, identifying the gain and phase contribution of the various elements in the loop is critical. Figure 4 shows the key equivalent elements of a boost converter. Because of the fast current control loop, the power stage of the IC, inductor, and diode have been replaced by the equivalent transconductance amplifier GMP. GMP acts as a current source where the output current is proportional to the VC voltage. Note that the maximum output current of GMP is finite due to the current limit in the IC. ESR Zero: Z2 = From Figure 4, the DC gain, poles and zeroes can be calculated as follows: Using the circuit of Figure 1 as an example, Table 3 shows the parameters used to generate the bode plot shown in Figure 5. Output Pole: P1 = 2 2 • π • RL • C OUT Error Amp Pole: P2 = Error Amp Zero: Z1 = DC Gain: A = 1 2 • π • RO • C C 1 2 • π • RC • C C GMP FS 3 Value Units RL 28 Ω Application Specific Comment COUT 2.2 µF Application Specific RO 10 MΩ Not Adjustable CC 270 pF Adjustable RC 27.4 kΩ Adjustable VOUT 12 V Application Specific VIN 5 V Application Specific GMA 40 µmho GMP Not Adjustable 5 mho L 2.2 µH Not Adjustable FS 2.7 MHz Not Adjustable ESR 10 mΩ Not Adjustable Application Specific VOUT + ESR + GMA 1.250V REFERENCE COUT R1 – CC 2 2 • π • VOUT • L High Frequency Pole: P3 > Parameter – RC RHP Zero: Z3 = Table 3. Bode Plot Parameters 1.25 • G MA • RO • G MP • RL VOUT VC 2 VIN • RL RO R2 RL From Figure 5, the phase when the gain reaches 0dB is 122° giving a phase margin of 58°. This is more than adequate. The cross-over frequency is 90kHz, which is about 30 times lower than the frequency of the right half plane zero Z2. It is important that the cross-over frequency be at least 3 times lower than the frequency of the RHP zero to achieve adequate phase margin. GMA: TRANSCONDUCTANCE AMPLIFIER INSIDE IC GMP: POWER STAGE TRANSCONDUCTANCE AMPLIFIER COUT: OUTPUT CAPACITOR RL: OUTPUT RESISTANCE DEFINED AS VOUT DIVIDED BY ILOAD (MAX) R1, R2: FEEDBACK RESISTOR DIVIDER NETWORK RO: OUTPUT RESISTANCE OF GMA RC: COMPENSATION RESISTOR CC: COMPENSATION CAPACITOR Figure 4. Boost Converter Equivalent Model sn1946a 1946afs 8 LT1946A U W U U APPLICATIO S I FOR ATIO Setting Output Voltage 100 To set the output voltage, select the values of R1 and R2 (see Figure 1) according to the following equation: GAIN (f) 50 V R1 = R2 OUT – 1 1.25V 0 A good range for R2 is from 5k to 30k. –50 100 1k 10k 100k FREQUENCY (Hz) 1M 1946A FO5a PHASE (f) 0 –100 Layout Hints The high speed operation of the LT1946A demands careful attention to board layout. You will not get advertised performance with careless layouts. Figure 6 shows the recommended component placement for a boost converter. GROUND PLANE CSS C1 58° CC VIN RC –180 –200 100 + 1 1k 10k 100k FREQUENCY (Hz) 1M 2 1946A FO5b R2 SHUTDOWN Figure 5. Gain and Phase Plots of Figure 1 Circuit Diode Selection A Schottky diode is recommended for use with the LT1946A. The Microsemi UPS120 is a very good choice. Where the input to output voltage differential exceeds 20V, use the UPS140 (a 40V diode). These diodes are rated to handle an average forward current of 1A. For applications where the average forward current of the diode is less than 0.5A, an ON Semiconductor MBR0520 diode can be used. 8 R1 LT1946A 7 3 6 4 5 L1 MULTIPLE VIAs GND C2 VOUT 19949 F04 NOTE: DIRECT HIGH CURRENT PATHS USING WIDE PC TRACES. MINIMIZE TRACE AREA AT PIN 1(VC) AND PIN 2(FB). USE MULTIPLE VIAS TO TIE PIN 4 COPPER TO GROUND PLANE. USE VIAS AT ONE LOCATION ONLY TO AVOID INTRODUCING SWITCHING CURRENTS INTO THE GROUND PLANE. Figure 6. Recommended Component Placement for Boost Converter sn1946a 1946afs 9 LT1946A U TYPICAL APPLICATIO S Low Profile (< 1.1mm Tall) Triple Output TFT Supply (10V, –10V, 20V) D2 D3 VON 20V 5mA C5 0.1µF L1 1.5µH VIN 5V OFF ON 3 8 + C1 4.7µF 7 CSS 100nF D1 6 VIN 5 SW R1 75k SHDN SS LT1946A COMP VC FB AVDD 10V 475mA 2 C2 20µF GND* 1 RC 59k CC 150pF 4 C1–C6: X5R or X7R C1: 4.7µF, 6.3V C2: 2× 10µF, 10V C3: 1µF, 25V C4: 2.2µF, 10V C5–C6: 0.1µF, 10V D1: MICROSEMI UPS120 OR EQUIVALENT D2–D5: ZETEX BAT54S OR EQUIVALENT L1: COILCRAFT LP01704-152MC * EXPOSED PAD MUST ALSO BE GROUNDED C3 1µF R2 10.5k C6 0.1µF D4 C4 2.2µF D5 VOFF –10V 10mA 1946A TA02 Transient Response Efficiency 90 85 AVDD 50mV/DIV AC COUPLED EFFICIENCY (%) 80 ILI 0.5A/DIV 75 70 65 60 VON LOAD = 5mA VOFF LOAD = 10mA 55 AVDD LOAD 350mA 200mA 50 100µs/DIV 1946A TA03 0 100 200 300 400 AVDD LOAD CURRENT (mA) 500 1946A TA04 sn1946a 1946afs 10 LT1946A U TYPICAL APPLICATIO S Triple Output TFT Supply Uses SEPIC Topology for Output Disconnect D2 VON 23V 10mA C4 0.22µF D3 VOFF –12V 10mA C5 0.22µF L1 10µH VIN 12V ± 10% 3 OFF ON 8 + 1 C1 2.2µF D1 6 VIN 5 SW C1–C5: X5R or X7R C1: 2.2µF, 6.3V C2: 2× 10µF, 16V C3: 1µF, 25V C4: 0.22µF, 25V C5: 0.22µF, 16V L2 10µH SHDN SS LT1946A FB R1 84.5k 2 C2 20µF VC COMP GND* 4 7 CSS 100nF C3 1µF AVDD 12V 250mA R2 9.76k D1: MICROSEMI UPS120 OR EQUIVALENT D2–D3: CENTRAL SEMI CMDSH-3 L1–L2: TDK RLF5018-100MR94 * EXPOSED PAD MUST ALSO BE GROUNDED 1946A TA09 MS8E Package 8-Lead Plastic MSOP (Reference LTC DWG # 05-08-1662) 0.889 ± 0.127 (.035 ± .005) 2.794 ± 0.102 (.110 ± .004) 5.23 (.206) MIN 0.42 ± 0.04 (.0165 ± .0015) TYP 2.083 ± 0.102 3.2 – 3.45 (.082 ± .004) (.126 – .136) 0.65 (.0256) BSC BOTTOM VIEW OF EXPOSED PAD OPTION 3.00 ± 0.102 (.118 ± .004) (NOTE 3) 0.254 (.010) 8 1 2.06 ± 0.102 (.080 ± .004) 1.83 ± 0.102 (.072 ± .004) 3.00 ± 0.102 (.118 ± .004) NOTE 4 4.88 ± 0.1 (.192 ± .004) DETAIL “A” 0.52 (.206) REF 7 6 5 0° – 6° TYP GAUGE PLANE 0.53 ± 0.015 (.021 ± .006) RECOMMENDED SOLDER PAD LAYOUT DETAIL “A” 1 2 3 4 1.10 (.043) MAX 8 0.86 (.34) REF 0.18 (.077) NOTE: 1. DIMENSIONS IN MILLIMETER/(INCH) 2. DRAWING NOT TO SCALE 3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX SEATING PLANE 0.22 – 0.38 (.009 – .015) 0.65 (.0256) BCS 0.13 ± 0.05 (.005 ± .002) MSOP (MS8E) 1001 sn1946a 1946afs 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. 11 LT1946A U TYPICAL APPLICATIO S Low Profile (< 1.1mm Tall) Triple Output TFT Supply (8V, – 8V, 24V) D2 D4 D3 C6 0.1µF C5 0.1µF D5 VON 23V 5mA C7 0.1µF Efficiency OFF ON 3 8 + C1 4.7µF 7 6 5 VIN SW LT1946A COMP VC 1 FB AVDD 8V 375mA 2 C2 20µF GND* 4 C4 1µF R3 5.23k CSS 100nF 85 80 R2 28.7k SHDN SS 90 D1 EFFICIENCY (%) L1 1.2µH VIN 3.3V 75 70 65 60 VON LOAD = 5mA VOFF LOAD = 10mA 55 C1–C8: X5R or X7R C1: 4.7µF, 6.3V C2: 2× 10µF, 10V C3: 2.2µF, 10V C4: 1µF, 25V C5, C6, C8: 0.1µF, 10V C7: 0.1µF, 16V D1: MICROSEMI UPS120 OR EQUIVALENT D2–D7: ZETEX BAT54S OR EQUIVALENT L1: COILCRAFT LP01704-122MC * EXPOSED PAD MUST ALSO BE GROUNDED C8 0.1µF 50 D7 C3 2.2µF 0 100 200 300 AVDD LOAD CURRENT (mA) 400 D6 1946A TA06 VOFF –8V 10mA 1946A TA05 Start-Up Waveforms Transient Response AVDD 5V/DIV AVDD 50mV/DIV AC COUPLED VON 10V/DIV ILI 0.5A/DIV VOFF 5V/DIV ILOAD 350mA 200mA IIN 0.5A/DIV 50µs/DIV 1946A TA07 1ms/DIV 1946A TA08 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1613 550mA (ISW), 1.4MHz, Step-Up DC/DC Converter VIN = 0.9V to 10V, VOUT to 34V, IQ = 3mA, ISD < 1µA, ThinSOTTM LT1615/LT1615-1 300mA/0.75mA (ISW), Constant Off-Time Step-Up DC/DC Converter VIN = 1V to 15V, VOUT to 34V, IQ = 20µA, ISD < 1µA, ThinSOT LT1930/LT1930A 1A (ISW), 1.2MHz/2.2MHz, Step-Up DC/DC Converter VIN = 2.6V to 16V, VOUT to 34V, IQ = 4.2mA/5.5mA, ISD < 1µA, ThinSOT LT1946 1.5A (ISW), 1.2MHz, Step-Up DC/DC Converter VIN = 2.45V to 16V, VOUT to 34V, IQ = 3.2mA, ISD < 1µA, MS8 LT1961 1.5A (ISW), 1.25MHz, Step-Up DC/DC Converter VIN = 3V to 25V, VOUT to 35V, IQ = 0.9mA, ISD < 6µA, MS8E ThinSOT is a trademark of Linear Technology Corporation. sn1946a 1946afs 12 Linear Technology Corporation LT/TP 1102 2K • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com LINEAR TECHNOLOGY CORPORATION 2001