LT1935ES5#TRMPBF

LT1935 1.2MHz Boost DC/DC Converter in ThinSOT with 2A Switch U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO 1.2MHz Switching Frequency High Output Voltage: Up to 38V Wide Input Range: 2.3V to 16V Low VCESAT Switch: 180mV at 2A Soft-Start Uses Small Surface Mount Components 5V at 1A from 3.3V Input 12V at 600mA from 5V Input Low Shutdown Current: < 1µA Pin-for-Pin Compatible with the LT1613 and LT1930 Low Profile (1mm) SOT-23 (ThinSOTTM) Package U APPLICATIO S ■ ■ ■ ■ ■ ■ ■ Digital Cameras Battery Backup LCD Bias Local 5V or 12V Supply PC Cards xDSL Power Supply TFT-LCD Bias Supply The LT®1935 is the industry’s highest power SOT-23 switching regulator. Its unprecedented 2A, 40V internal switch allows high output currents to be generated in a small footprint. Intended for space-conscious applications, the LT1935 switches at 1.2MHz, allowing the use of tiny, low profile inductors and capacitors 2mm or less in height. The NPN switch achieves a VCESAT of just 180mV at 2A independent of supply voltage, resulting in high efficiency even at maximum power levels from a 3V input. A constant frequency, internally compensated, current mode PWM architecture results in low, predictable output noise that is easy to filter. Low ESR ceramic capacitors can be used on the output, further reducing noise to the millivolt level. The high voltage switch on the LT1935 is rated at 40V, making the device ideal for boost converters up to 38V as well as for single-ended primary inductance converter (SEPIC) and flyback designs. The device can generate 5V at up to 1A from a 3.3V supply or 5V at 550mA from four alkaline cells in a SEPIC design. The LT1935 is available in a 5-lead SOT-23 package. , LTC and LT are registered trademarks of Linear Technology Corporation. ThinSOT is a trademark of Linear Technology Corporation. U TYPICAL APPLICATIO 4.7µF VIN D1 SW VOUT 12V 600mA 80 84.5k LT1935 10µF ON OFF SHDN FB GND VIN = 5V 85 10k EFFICIENCY (%) L1 4.2µH VIN 5V Efficiency, VOUT = 12V 90 VIN = 3.3V 75 70 65 60 D1: ON SEMI MBRM120 L1: SUMIDA CDRH5D28-4R2 1935 F01 Figure 1. 5V to 12V, 600mA Step-Up DC/DC Converter 55 50 0 100 200 300 400 500 600 700 LOAD CURRENT (mA) 1935 F01b 1935f 1 LT1935 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 40V FB Voltage ................................................................. 6V Current Into FB Pin .............................................. ±1mA SHDN Voltage ......................................................... 16V Maximum Junction Temperature ......................... 125°C Operating Ambient Temperature Range (Note 2) .............................................. – 40°C to 85°C Storage Temperature Range ................. – 65°C to 150°C Strict adherence to JDEC 020B solder attach and rework for assemblies containing lead is recommended. ORDER PART NUMBER TOP VIEW SW 1 LT1935ES5 5 VIN GND 2 FB 3 4 SHDN S5 PART MARKING S5 PACKAGE 5-LEAD PLASTIC TSOT-23 LTRX TJMAX = 125°C, θJA = 113°C/ W, 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 = 25°C. VIN = 3V, VSHDN = VIN unless otherwise noted. (Note 2) PARAMETER CONDITIONS Feedback Voltage Measured at the FB Pin Feedback Voltage Line Regulation 2.5V ≤ VIN ≤ 16V FB Pin Bias Current VFB = VREF ● MIN TYP MAX UNITS 1.240 1.265 1.280 V 0.01 ● Undervoltage Lockout Threshold 12 60 nA 2.1 2.3 V 16 V 1.4 MHz Maximum Input Voltage Switching Frequency ● Maximum Duty Cycle Switch Current Limit (Note 3) Switch Saturating Voltage ISW = 2A Switch Leakage Current VSW = 5V SHDN Pin Input Current VSHDN = 1.8V 1 1.2 85 93 % 2 3.2 A ● 180 280 mV 0.01 1 µA 14 40 µA VSHDN = 0V 0.1 Operating Supply Current VFB = 1.5V 3 SHDN Supply Current VSHDN = 0V 0.1 SHDN Input High Voltage SHDN Input Low Voltage Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: The LT1935ES5 is guaranteed to meet performance specifications from 0°C to 70°C. Specifications over the – 40°C to 85°C operating %/V µA mA 1 1.8 µA V 0.5 V temperature range are assured by design, characterization and correlation with statistical process controls. Note 3: Current limit guaranteed by design and/or correlation to static test. 1935f 2 LT1935 U W TYPICAL PERFOR A CE CHARACTERISTICS FB Pin Voltage Undervoltage Lockout Oscillator Frequency 1.6 1.28 2.4 1.4 1.26 2.2 1.0 UVLO (V) FREQUENCY (MHz) VFB (V) 2.3 1.2 1.27 0.8 0.6 2.0 0.4 1.25 1.9 0.2 1.24 –50 –25 0 25 50 75 100 0 –50 –25 125 0 25 50 75 100 Current Limit TYP MIN 2 1 400 4 300 3 TA = 85°C 200 TA = 25°C 80 100 0.5 0 1.0 1.5 2.0 SWITCH CURRENT (A) 2.5 SHDN Pin Current 3.0 0 0 0.5 1.0 1.5 2.0 SHDN VOLTAGE (V) 1935 G06 Frequency Foldback 1.4 SWITCHING FREQUENCY (MHz) TA = 25°C 60 40 20 0 2 1935 G05 1935 G04 80 50% DUTY CYCLE TA = 25°C 1 100 0 60 40 DUTY CYCLE (%) SHDN PIN CURRENT (µA) CURRENT LIMIT (A) 3 125 Peak Switch Current vs SHDN Pin Voltage (Soft-Start) CURRENT LIMIT (A) SWITCH SATURATION VOLTAGE (mV) TA = 25°C 100 1935 G03 Switch Saturation Voltage 4 20 50 25 75 0 TEMPERATURE (°C) 1935 G02 1935 G01 0 1.8 –50 –25 125 TEMPERATURE (°C) TEMPERATURE (°C) 0 2.1 TA = 25°C 1.2 1.0 0.8 0.6 0.4 0.2 0 0 2 10 12 4 8 6 SHDN PIN VOLTAGE (V) 14 16 1935 G07 0 0.2 1.0 0.4 0.6 0.8 FEEDBACK VOLTAGE (V) 1.2 1.4 1935 G08 1935f 3 LT1935 U U U PI FU CTIO S SW (Pin 1): Switch Pin. Connect inductor/diode here. Minimize trace area at this pin to reduce EMI. SHDN (Pin 4): Shutdown Pin. Tie to 1.8V or more to enable device. Ground to shut down. This pin also provides a softstart function; see Applications Information section. GND (Pin 2): Ground. Tie directly to local ground plane. VIN (Pin 5): Input Supply Pin. Must be locally bypassed. FB (Pin 3): Feedback Pin. Reference voltage is 1.265V. Connect resistive divider tap here. Minimize trace area at FB. Set VOUT according to VOUT = 1.265V(1 + R1/R2). W BLOCK DIAGRA 1.265V REFERENCE VIN 5 – A1 – FB 3 1 SW COMPARATOR + RC + DRIVER A2 R Q1 Q S CC SHDN 4 + Σ 0.01Ω x15 – VOUT RAMP GENERATOR R1 (EXTERNAL) 2 GND FB 1.2MHz OSCILLATOR R2 (EXTERNAL) 1935 BD Figure 2. Block Diagram U OPERATIO The LT1935 uses a constant frequency, current mode control scheme to provide excellent line and load regulation. Operation can be best understood by referring to the Block Diagram in Figure 2. At the start of each oscillator cycle, the SR latch is set, turning on the power switch Q1. A voltage proportional to the switch current 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 is set by error amplifier A1, and is simply an amplified version of the difference between the feedback voltage and the reference voltage of 1.265V. In this manner, the error amplifier sets the correct peak current level to keep the output in regulation. If the error amplifier’s output increases, more current is delivered to the output; if it decreases, less current is delivered. A clamp on the output of A1 (not shown) limits the switch current to 3A. A1’s output is also clamped to the voltage on the SHDN pin, providing a soft-start function by controlling the peak switch current during start-up. 1935f 4 LT1935 U W U U APPLICATIONS INFORMATION Inductor Selection Use inductors that are intended for high frequency power applications. The saturation current rating should be at least 2A. The RMS current rating, which is usually based on heating of the inductor, should be higher than the average current in the inductor in your application. For best efficiency, the DC resistance should be less than 100mΩ. A good first choice for the inductor value results in a ripple current that is 1/3 of the maximum switch current: L = 3 (VIN/VOUT) (VOUT – VIN)/(IMAX • f) IMAX is the maximum switch current of 2A and f is the switching frequency. At lower duty cycles (less than 70%), this value can be lowered somewhat in order to use a physically smaller inductor. Table 1 lists several inductor manufacturers, along with part numbers for inductors that are a good match to the LT1935. Table 1. Inductor Suppliers Supplier Model Prefix Sumida CDRH4D18, CDRH4D28, CDRH5D18, CDRH5D28, CR43 Coiltronics/Cooper SD10, SD12, SD18, SD20 .. Wurth Elektronik WE-PD2S, WE-PD3S, WE-PD4S Coilcraft MSS5131, MSS6132, DO1608 Use a 4.7µF ceramic capacitor to bypass the input of the LT1935. Be aware that the switching regulators require a low impedance input supply. Additional bulk capacitance may be required if the LT1935 circuit is more than a few inches away from the power source. If there are low ESR capacitors nearby, the input bypass capacitor can be reduced to 2.2µF. The output capacitor supports the output under transient loads and stabilizes the control loop of the LT1935. Look at the typical application circuits as a starting point to choose a value. Generally, a higher output capacitance is required at higher load currents and lower input voltages. Figure 3 shows transient response of the circuit in Figure 1. The load is stepped from 200mA to 400mA and back to 200mA. The transient performance can be improved by increasing the output capacitance, but may require a phase lead capacitor between the output and the FB pin. Figure 4 shows the transient response with the output capacitor increased to 20µF. Figure 5 shows the additional improvement resulting from the phase lead capacitor. VOUT 100mV/DIV ILOAD 200mA/DIV Diode Selection Use a Schottky rectifier with a 1A or higher current rating, such as the On Semiconductor MBRM120. Its 20V reverse voltage rating is adequate for most applications. Higher output voltages may require a 30V of 40V diode. 0 50µs/DIV 1935 F03 Figure 3. Transient Response of the Circuit in Figure 1, COUT = 10µF Capacitor Selection Use capacitors with low ESR (equivalent series resistance). In most cases, multilayer ceramic capacitors are the best choice. They offer high performance (very low ESR) in a small package. Use only X5R or X7R types; they maintain their capacitance over temperature and applied voltage. Other suitable capacitor types include low-ESR tantalum capacitors that are specified for power applications, and newer types of capacitors such as Sanyo’s POSCAP and Panasonic’s SP CAP. VOUT 100mV/DIV ILOAD 200mA/DIV 50µs/DIV 1935 F04 Figure 4. Transient Response with COUT = 20µF 1935f 5 LT1935 U U W U APPLICATIONS INFORMATION Soft Start The SHDN pin can be used to soft start the LT1935, reducing the maximum input current during start up. The SHDN pin is driven through an external RC filter to create a ramp at this pin. Figure 6 shows the start-up waveforms with and without the soft start circuit. Without soft start, the input current peaks at ~3A. With soft start, the peak current is reduced to 1A. By choosing a large RC time constant, the peak start-up current can be reduced to the current that is required to regulate the output, with no overshoot. Choose the value of the resistor so that it can supply 100µA when the SHDN pin reaches 1.8V. VOUT 100mV/DIV ILOAD 200mA/DIV 1935 F05 50µs/DIV OUT 84.5k 68pF 20µF FB 10k Figure 5. Transient Response with a 68pF Phase-Lead Capacitor RUN 5V/DIV RUN 5V/DIV VOUT 2V/DIV VOUT 2V/DIV IIN 1A/DIV IIN 1A/DIV 1935 F06a 20µs/DIV 200µs/DIV 1935 F06b 10k RUN SHDN SHDN RUN GND 0.22µF GND Figure 6. Adding a Resistor and Capacitor to the SHDN Pin Reduces the Peak Input Current During Start-Up. VIN = 3.3V, VOUT = 5V, C2 = 20µF, Output Load = 10Ω. Layout Hints L1 D1 The high speed operation of the LT1935 demands careful attention to board layout. You will not get advertised performance with careless layout. Figure 7 shows the recommended component placement. Make the ground pin copper area large. This helps to lower the die temperature. C1 + VIN VOUT + C2 SHDN R2 GND R1 C3 1935 F03 Figure 7. Suggested Layout 1935f 6 LT1935 U TYPICAL APPLICATIO S Efficiency, VOUT = 5V 5V Boost Converter C1 4.7µF ON OFF VIN SW LT1935 SHDN C3 150pF R1 29.4k 85 VOUT 5V 1A, VIN = 3.3V 0.6A, VIN = 2.5V D1 C2 20µF FB R2 10k GND VIN = 3.3V 80 EFFICIENCY (%) L1 1.8µH VIN 2.3V TO 4.8V 90 VIN = 2.5V 75 70 65 60 55 C1, C2: X5R OR X7R 6.3V D1: ON SEMI MBRM120 L1: SUMIDA CR43-1R8 1935 TA01 50 0 200 400 600 800 1000 1200 LOAD CURRENT (mA) 3.3V to 12V Boost Converter L1 4.2µH VIN 3.3V VIN C1 4.7µF D1 SW 47pF LT1935 ON OFF VOUT 12V 320mA SHDN R1 84.5k FB C2 22µF R2 10k GND D1: ON SEMI MBRM120 L1: SUMIDA CDRH5D28-4R2 1935 TA02 U PACKAGE DESCRIPTIO S5 Package 5-Lead Plastic TSOT-23 (Reference LTC DWG # 05-08-1635) 0.62 MAX 0.95 REF 2.90 BSC (NOTE 4) 1.22 REF 1.4 MIN 3.85 MAX 2.62 REF 2.80 BSC 1.50 – 1.75 (NOTE 4) PIN ONE RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR 0.95 BSC 0.30 – 0.45 TYP 5 PLCS (NOTE 3) 0.80 – 0.90 0.20 BSC 0.01 – 0.10 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 1.90 BSC 0.09 – 0.20 (NOTE 3) 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 S5 TSOT-23 0302 1935f 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 LT1935 U TYPICAL APPLICATIO S 8V, 16V and –8V TFT LCD Power Supply VIN 3.3V D2B D2A C5 0.1µF L1 2.2µH C3 1µF 16V 10mA 8V 450mA D1 VIN C1 4.7µF SW R1 100k LT1935 ON OFF SHDN C2 10µF FB R2 18.7k GND C1: X5R OR X7R 6.3V C2, C4, C5, C6: X5R OR X7R 10V C3: X5R OR X7R 25V D1: MBRM120 OR EQUIVALENT D2, D3: BAT-54S OR EQUIVALENT L1: SUMIDA CDRH4D28-2R2 C6 0.1µF D3A D3B C4 1µF –8V 10mA 1935 TA03 5V SEPIC Converter C3 2.2µF L1 4.7µH VIN 3.2V TO 9V C1 4.7µF ON OFF SW VIN LT1935 SHDN R1 29.4k D1 VOUT 5V 425mA, VIN >3.2V 500mA, VIN >3.6V 550mA, VIN >4V 47pF C2 47µF FB GND C1, C3: X5R OR X7R 10V C2: X5R OR X7R 6.3V R2 10k L2 4.7µH D1: ON SEMI MBRM120 L1, L2: SUMIDA CDRH4D18-4R7 1935 TA04 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1618 1.5A (ISW), 1.25MHz, High Efficiency Step-Up DC/DC Converter VIN: 1.6V to 18V, VOUT(MAX): 35V, IQ: 1.8mA, ISD: