LT1931/LT1931A 1.2MHz/2.2MHz Inverting DC/DC Converters in ThinSOT U FEATURES DESCRIPTIO ■ The LT®1931/LT1931A are the industry’s highest power inverting SOT-23 current mode DC/DC converters. Both parts include a 1A integrated switch allowing high current outputs to be generated in a small footprint. The LT1931 switches at 1.2MHz while the LT1931A switches at 2.2MHz. These high speeds enable the use of tiny, low cost capacitors and inductors 2mm or less in height. The LT1931 is capable of generating – 5V at 350mA or –12V at 150mA from a 5V supply, while the LT1931A can generate –5V at 300mA using significantly smaller inductors. Both parts are easy pin-for-pin upgrades for higher power LT1611 applications. ■ ■ ■ ■ ■ ■ ■ ■ ■ Fixed Frequency 1.2MHz/2.2MHz Operation Very Low Noise: 1mVP-P Output Ripple – 5V at 350mA from 5V Input –12V at 150mA from 5V Input Uses Small Surface Mount Components Wide Input Range: 2.6V to 16V Low Shutdown Current: <1µA Low VCESAT Switch: 400mV at 1A Pin-for-Pin Compatible with the LT1611 Low Profile (1mm) ThinSOTTM Package U APPLICATIO S ■ ■ ■ ■ ■ Disk Drive MR Head Bias Digital Camera CCD Bias LCD Bias GaAs FET Bias Local Low Noise/Low Impedance Negative Supply The LT1931/LT1931A operate in a dual inductor inverting topology that filters both the input side and output side current. Very low output voltage ripple approaching 1mVP-P can be achieved when ceramic output capacitors are used. Fixed frequency switching ensures a clean output free from low frequency noise typically present with charge pump solutions. The low impedance output remains within 1% of nominal during large load steps. The 36V switch allows VIN to VOUT differential of up to 34V. The LT1931/LT1931A are available in the 5-lead ThinSOT package. , LTC and LT are registered trademarks of Linear Technology Corporation. ThinSOT is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. U TYPICAL APPLICATIO C2 1µF L1A 10µH VIN 5V Efficiency L1B 10µH 100 95 VIN SW SHDN C1 4.7µF R1 29.4k LT1931 C4 220pF NFB GND R2 10k VOUT –5V 350mA C3 22µF 90 EFFICIENCY (%) D1 85 80 75 70 65 60 C1: TAIYO YUDEN X5R JMK212BJ475MG C2: TAIYO YUDEN X5R LMK212BJ105MG C3: TAIYO YUDEN X5R JMK325BJ226MM D1: ON SEMICONDUCTOR MBR0520 L1: SUMIDA CLS62-100 Figure 1. 5V to –5V, 350mA Inverting DC/DC Converter 1931 F01 55 50 0 50 100 150 200 250 LOAD CURRENT (mA) 300 350 1931 TA01 1931fa 1 LT1931/LT1931A 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 NFB Voltage ............................................................. – 2V Current Into NFB 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 TOP VIEW SW 1 5 VIN GND 2 4 SHDN NFB 3 S5 PACKAGE 5-LEAD PLASTIC TSOT-23 TJMAX = 125°C, θJA = 150°C/ W ORDER PART NUMBER LT1931ES5 LT1931AES5 LT1931IS5 LT1931AIS5 S5 PART MARKING LTRA LTSP LTBZF LTBZG Order Options Tape and Reel: Add #TR Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF Lead Free Part Marking: http://www.linear.com/leadfree/ 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 MIN Minimum Operating Voltage LT1931 TYP MAX 2.45 2.6 Maximum Operating Voltage MIN LT1931A TYP MAX 2.45 16 Feedback Voltage ● NFB Pin Bias Current VNFB = –1.255V Quiescent Current VSHDN = 2.4V, Not Switching – 1.275 – 1.255 – 1.235 – 1.280 – 1.230 ● UNITS 2.6 V 16 V –1.275 –1.255 –1.235 –1.280 –1.230 V V 4 8 8 16 µA 4.2 6 5.8 8 mA Quiescent Current in Shutdown VSHDN = 0V, VIN = 3V 0.01 1 0.01 1 µA Reference Line Regulation 2.6V ≤ VIN ≤ 16V 0.01 0.05 0.01 0.05 %/V 1.4 1.6 1.8 1.6 2.2 2.6 2.9 MHz MHz 75 82 Switching Frequency Maximum Duty Cycle Switch Current Limit (Note 3) Switch VCESAT ISW = 1A Switch Leakage Current VSW = 5V SHDN Input Voltage, High 1 0.85 1.2 ● ● 84 90 1 1.2 2 400 600 0.01 1 2.4 1.2 2.5 A 400 600 mV 0.01 1 µA 2.4 SHDN Input Voltage, Low SHDN Pin Bias Current 1 V 0.5 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 LT1931E/LT1931AE are guaranteed to meet performance specifications from 0°C to 70°C. Specifications over the – 40°C to 85°C % 16 0 32 0.1 35 0 0.5 V 70 0.1 µA µA operating temperature range are assured by design, characterization and correlation with statistical process controls. LT1931I/LT1931AI are guaranteed over the –40°C to 85°C temperature range. Note 3: Current limit guaranteed by design and/or correlation to static test. 1931fa 2 LT1931/LT1931A U W TYPICAL PERFOR A CE CHARACTERISTICS Quiescent Current Feedback Pin Voltage 7.0 90 NOT SWITCHING 80 6.5 LT1931A 5.5 5.0 4.5 LT1931 4.0 SHDN PIN CURRENT (µA) –1.27 6.0 FEEDBACK VOLTAGE (V) QUIESCENT CURRENT (mA) Shutdown Pin Current –1.28 –1.26 –1.25 –1.24 60 50 40 30 LT1931 20 0 3.0 –50 –25 0 50 25 TEMPERATURE (°C) 75 –1.22 –50 100 –25 0 25 50 TEMPERATURE (°C) 75 –10 100 0 Current Limit 1.2 VCESAT (V) 0.6 TA = 25°C 0.40 2.3 0.35 2.1 0.25 0.20 0.15 1.9 1.5 1.3 0.9 0.2 0.05 0.7 0 30 40 50 60 70 DUTY CYCLE (%) 80 0 90 0.2 0.4 0.6 0.8 SWITCH CURRENT (A) 1.0 1.2 LT1931 1.1 0.10 20 LT1931A 1.7 0.4 10 6 Oscillator Frequency 0.30 0.8 5 2.5 FREQUENCY (MHz) TA = 25°C 1.4 1.0 3 4 2 SHDN PIN VOLTAGE (V) 1931 G03 Switch Saturation Voltage 0.45 1.6 1 1931 G02 1931 G01 CURRENT LIMIT (A) LT1931A 70 10 –1.23 3.5 0 TA = 25°C 0.5 –50 –25 25 50 0 TEMPERATURE (°C) 100 1931 G06 1931 G05 1931 G04 75 U U U PI FU CTIO S SW (Pin 1): Switch Pin. Connect inductor/diode here. Minimize trace area at this pin to keep EMI down. GND (Pin 2): Ground. Tie directly to local ground plane. NFB (Pin 3): Feedback Pin. Reference voltage is –1.255V. Connect resistive divider tap here. Minimize trace area. The NFB bias current flows out of the pin. Set R1 and R2 according to: For LT1931: R1 = | VOUT | – 1.255 1.255 + 4 • 10 – 6 R2 ( For LT1931A: R1 = | VOUT | – 1.255 1.255 + 8 • 10 – 6 R2 ( ) SHDN (Pin 4): Shutdown Pin. Tie to 2.4V or more to enable device. Ground to shut down. VIN (Pin 5): Input Supply Pin. Must be locally bypassed. ) 1931fa 3 LT1931/LT1931A W BLOCK DIAGRA VIN 5 VIN R5 80k R6 80k 1 SW + – Q1 VOUT CPL (OPTIONAL) Q2 x10 – A1 gm RC Σ RAMP GENERATOR + COMPARATOR A2 R LATCH S DRIVER Q3 Q + CC R3 30k R1 (EXTERNAL) NFB R2 (EXTERNAL) 0.01Ω – 1.2MHz OSCILLATOR R4 150k SHDN 3 NFB 4 SHUTDOWN 2 GND 1931 BD Figure 2 U OPERATIO The LT1931 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 Q3. 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 the error amplifier (gm) and is simply an amplified version of the difference between the feedback voltage and the reference voltage of –1.255V. 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 taken from the output; if it decreases, less current is taken. One function not shown in Figure 2 is the current limit. The switch current is constantly monitored and not allowed to exceed the nominal value of 1.2A. If the switch current reaches 1.2A, the SR latch is reset regardless of the state of comparator A2. This current limit protects the power switch as well as various external components connected to the LT1931. The Block Diagram for the LT1931A is identical except that the oscillator is 2.2MHz and resistors R3 to R6 are one-half the LT1931 values. 1931fa 4 LT1931/LT1931A U W U U APPLICATIO S I FOR ATIO LT1931A AND LT1931 DIFFERENCES: Switching Frequency The key difference between the LT1931A and LT1931 is the faster switching frequency of the LT1931A. At 2.2MHz, the LT1931A switches at nearly twice the rate of the LT1931. Care must be taken in deciding which part to use. The high switching frequency of the LT1931A allows smaller cheaper inductors and capacitors to be used in a given application, but with a slight decrease in efficiency and maximum output current when compared to the LT1931. Generally, if efficiency and maximum output current are critical, the LT1931 should be used. If application size and cost are more important, the LT1931A will be the better choice. In many applications, tiny inexpensive chip inductors can be used with the LT1931A, reducing solution cost. core losses at frequencies above 1MHz are much lower for ferrite cores than for powdered-iron units. When using coupled inductors, choose one that can handle at least 1A of current without saturating, and ensure that the inductor has a low DCR (copper-wire resistance) to minimize I2R power losses. If using uncoupled inductors, each inductor need only handle one-half of the total switch current so that 0.5A per inductor is sufficient. A 4.7µH to 15µH coupled inductor or a 15µH to 22µH uncoupled inductor will usually be the best choice for most LT1931 designs. For the LT1931A, a 2.2µH to 4.7µH coupled inductor or a 3.3µH to 10µH uncoupled inductor will usually suffice. In certain applications such as the “Charge Pump” inverting DC/DC converter, only a single inductor is used. In this case, the inductor must carry the entire 1A switch current. Table 1. Recommended Inductors—LT1931 L (µH) Size (L × W × H) mm CLS62-100 CR43-150 CR43-220 10 15 22 6.8 × 6.6 × 2.5 4.5 × 4.0 × 3.2 Sumida (847) 956-0666 www.sumida.com CTX10-1 CTX15-1 10 15 8.9 × 11.4 × 4.2 Coiltronics (407) 241-7876 www. coiltronics.com LQH3C100K24 LQH4C150K04 10 15 3.2 × 2.5 × 2.0 Murata (404) 436-1300 www.murata.com PART Duty Cycle The maximum duty cycle (DC) of the LT1931A is 75% compared to 84% for the LT1931. The duty cycle for a given application using the dual inductor inverting topology is given by: | VOUT | DC = | VIN | + | VOUT | For a 5V to –5V application, the DC is 50% indicating that the LT1931A can be used. A 5V to –16V application has a DC of 76.2% making the LT1931 the right choice. The LT1931A can still be used in applications where the DC, as calculated above, is above 75%. However, the part must be operated in the discontinuous conduction mode so that the actual duty cycle is reduced. INDUCTOR SELECTION Several inductors that work well with the LT1931 are listed in Table 1 and those for the LT1931A are listed in Table 2. Besides these, there are many other inductors that can be used. Consult each manufacturer for detailed information and for their entire selection of related parts. Ferrite core inductors should be used to obtain the best efficiency, as VENDOR Table 2. Recommended Inductors—LT1931A PART L (µH) Size (L × W × H) mm ELJPC3R3MF ELJPC4R7MF 3.3 4.7 2.5 × 2.0 × 1.6 Panasonic (408) 945-5660 www.panasonic.com CLQ4D10-4R71 CLQ4D10-6R82 4.7 6.8 7.6 × 4.8 × 1.8 Sumida (847) 956-0666 www.sumida.com LB20164R7M LB20163R3M 4.7 3.3 2.0 × 1.6 × 1.6 Taiyo Yuden (408) 573-4150 www.t-yuden.com LQH3C4R7K24 LQH4C100K24 4.7 10 3.2 × 2.5 × 2.0 Murata (404) 436-1300 www.murata.com VENDOR 1Use drawing #5382-T039 2Use drawing #5382-T041 1931fa 5 LT1931/LT1931A U W U U APPLICATIO S I FOR ATIO The inductors shown in Table 2 for use with the LT1931A were chosen for their small size. For better efficiency, use similar valued inductors with a larger volume. For instance, the Sumida CR43 series, in values ranging from 3.3µH to 10µH, will give a LT1931A application a few percentage points increase in efficiency. 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 their capacitance over wide voltage and temperature ranges. A 10µF to 22µF output capacitor is sufficient for most LT1931 applications while a 4.7µF to 10µF capacitor will suffice for the LT1931A. Solid tantalum or OS-CON 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 LT1931/LT1931A. A 1µF to 4.7µF input capacitor is sufficient for most applications. Table 3 shows a list of several ceramic capacitor manufacturers. Consult the manufacturers for detailed information on their entire selection of ceramic parts. Table 3. 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 The decision to use either low ESR (ceramic) capacitors or the higher ESR (tantalum or OS-CON) capacitors can effect the stability of the overall system. The ESR of any capacitor, along with the capacitance itself, contributes a zero to the system. For the tantalum and OS-CON capacitors, this zero is located at a lower frequency due to the higher value of the ESR, while the zero of a ceramic capacitor is at a much higher frequency and can generally be ignored. A phase lead zero can be intentionally introduced by placing a capacitor (C4) in parallel with the resistor (R1) between VOUT and VNFB as shown in Figure 1. The frequency of the zero is determined by the following equation. ƒZ = 1 2π • R1 • C4 By choosing the appropriate values for the resistor and capacitor, the zero frequency can be designed to improve the phase margin of the overall converter. The typical target value for the zero frequency is between 20kHz to 60kHz. Figure 3 shows the transient response of the inverting converter from Figure 1 without the phase lead capacitor C4. The phase margin is reduced as evidenced by more ringing in both the output voltage and inductor current. A 220pF capacitor for C4 results in better phase margin, which is revealed in Figure 4 as a more damped response and less overshoot. Figure 5 shows the transient response when a 22µF tantalum capacitor with no phase lead capacitor is used on the output. The higher output voltage ripple is revealed in the upper waveform as a thicker line. The transient response is adequate which implies that the ESR zero is improving the phase margin. VOUT 20mV/DIV AC COUPLED IL1A + IL1B 0.5A/DIV AC COUPLED LOAD 200mA CURRENT 100mA 100µs/DIV 1931 F03 Figure 3. Transient Response of Inverting Converter Without Phase Lead Capacitor 1931fa 6 LT1931/LT1931A U W U U APPLICATIO S I FOR ATIO VOUT 20mV/DIV AC COUPLED VOUT 2V/DIV IL1A + IL1B 0.5A/DIV AC COUPLED IIN 0.5A/DIV AC COUPLED LOAD 200mA CURRENT 100mA VSHDN 5V 0V 100µs/DIV 1931 F04 500µs/DIV Figure 4. Transient Response of Inverting Converter with 220pF Phase Lead Capacitor Figure 6. Start-Up Waveforms for 5V to – 5V Application (Figure 1). No Soft-Start Circuit. VOUT Reaches – 5V in 500µs; Input Current Peaks at 800mA VOUT 0.1V/DIV AC COUPLED regulator tries to charge up the output capacitor as quickly as possible, which results in a large inrush current. Figure 6 shows a typical oscillograph of the start-up waveform for the application of Figure 1 starting into a load of 33Ω. The lower waveform shows SHDN being pulsed from 0V to 5V. The middle waveform shows the input current, which reaches as high as 0.8A. The total time required for the output to reach its final value is approximately 500µs. For some applications, this initial inrush current may not be acceptable. If a longer start-up time is acceptable, a soft-start circuit consisting of RSS and CSS, as shown in Figure 7, can be used to limit inrush current to a lower value. Figure 8 shows the relevant waveforms with RSS = 15k and CSS = 33nF. Input current, measured at VIN, is limited to a peak value of 0.5A as the time required to reach final value increases to 1ms. In Figure 9, CSS is IL1A + IL1B 0.5A/DIV AC COUPLED LOAD 200mA CURRENT 100mA 50µs/DIV 1931 F05 Figure 5. Transient Response of Inverting Converter with 22µF Tantalum Output Capacitor and No Phase Lead Capacitor START-UP/SOFT-START For most LT1931/LT1931A applications, the start-up inrush current can be high. This is an inherent feature of switching regulators in general since the feedback loop is saturated due to VOUT being far from its final value. The CURRENT PROBE + RSS 15k C2 1µF L1A 10µH VIN 5V VIN SW SHDN R1 29.4k NFB GND D2 1N4148 CSS 33nF/68nF VOUT L1B 10µH D1 C1 4.7µF LT1931 VSS 1931 F06 R2 10k C1: TAIYO YUDEN X5R JMK212BJ475MG C2: TAIYO YUDEN X5R LMK212BJ105MG C3: TAIYO YUDEN XR5 JMK325BJ226MM D1: ON SEMICONDUCTOR MBR0520 L1: SUMIDA CLS62-100 C4 220pF VOUT –5V C3 22µF 1931 F07 Figure 7. RSS and CSS at SHDN Pin Provide Soft-Start to LT1931 Inverting Converter 1931fa 7 LT1931/LT1931A U W U U APPLICATIO S I FOR ATIO DIODE SELECTION VOUT 2V/DIV IIN 0.5A/DIV AC COUPLED VSS 5V 0V 200µs/DIV 1931 F08 A Schottky diode is recommended for use with the LT1931/ LT1931A. The Motorola MBR0520 is a very good choice. Where the input to output voltage differential exceeds 20V, use the MBR0530 (a 30V diode). These diodes are rated to handle an average forward current of 0.5 A. In applications where the average forward current of the diode exceeds 0.5A, a Microsemi UPS5817 rated at 1A is recommended. Figure 8. RSS = 15k, CSS = 33nF; VOUT Reaches – 5V in 1ms; Input Current Peaks at 500mA LAYOUT HINTS The high-speed operation of the LT1931/LT1931A demands careful attention to board layout. You will not get advertised performance with careless layout. Figure 10 shows the recommended component placement. The ground cut at the cathode of D1 is essential for low noise operation. VOUT 2V/DIV IIN 0.5A/DIV AC COUPLED VSS 5V 0V 500µs/DIV 1931 F09 Figure 9. RSS = 15k, CSS = 68nF; VOUT Reaches – 5V in 1.6ms; Input Current Peaks at 350mA L1B L1A C1 D1 + C2 VIN C3 + increased to 68nF, resulting in a lower peak input current of 350mA with a VOUT ramp time of 1.6ms. CSS or RSS can be increased further for an even slower ramp, if desired. Diode D2 serves to quickly discharge CSS when VSS is driven low to shut down the device. D2 can be omitted, resulting in a “soft-stop” slow discharge of the output capacitor. –VOUT 5 1 2 3 4 SHUTDOWN R2 GND R1 1931 F10 Figure 10. Suggested Component Placement. Note Cut in Ground Copper at D1’s Cathode 1931fa 8 LT1931/LT1931A U TYPICAL APPLICATIO S 5V to –12V Inverting Converter C2 1µF L1A 10µH VIN 5V Efficiency 100 L1B 10µH 95 90 D1 SHDN R1 84.5k LT1931 C1 4.7µF VOUT –12V 150mA SW C3 10µF NFB GND R2 10k 85 EFFICIENCY (%) VIN 80 75 70 65 60 55 C1: TAIYO YUDEN X5R JMK212BJ475MG C2: TAIYO YUDEN X5R TMK316BJ105ML C3: TAIYO YUDEN X5R EMK325BJ106MM D1: ON SEMICONDUCTOR MBR0520 L1: SUMIDA CLS62-100 50 1931 TA02 0 25 75 100 50 LOAD CURRENT (mA) 125 150 1931 TA03 5V to – 5V Inverting Converter Using Uncoupled Inductors C2 1µF L1 10µH VIN 5V L2 10µH D1 VIN SHDN C1 4.7µF VOUT –5V 300mA SW R1 29.4k LT1931 220pF C3 22µF NFB GND R2 10k C1: TAIYO YUDEN X5R JMK212BJ475MG C2: TAIYO YUDEN X5R LMK212BJ105MG C3: TAIYO YUDEN X5R JMK212BJ226MM D1: ON SEMICONDUCTOR MBR0520 L1, L2: MURATA LQH3C100K04 1931 TA04 2.2MHz, 5V to – 5V Inverting Converter C2 1µF L1 4.7µH VIN 5V Efficiency 80 L2 4.7µH VIN SW SHDN C1 4.7µF R1 28.7k LT1931A NFB GND R2 10k C4 180pF VOUT –5V 300mA C3 4.7µF EFFICIENCY (%) 75 D1 70 65 60 55 C1: TAIYO YUDEN X5R JMK212BJ475MG C2: TAIYO YUDEN X5R LMK212BJ105MG C3: TAIYO YUDEN X5R JMK212BJ475MG D1: ON SEMICONDUCTOR MBR0520 L1, L2: MURATA LQH3C4R7M24 1931 TA05a 50 0 50 100 150 200 250 LOAD CURRENT (mA) 300 350 1931 TA05b 1931fa 9 LT1931/LT1931A U TYPICAL APPLICATIO S 2.2MHz, 5V to –5V Converter Uses Tiny Chip Inductors C2 1µF L1 3.3µH VIN 5V Efficiency 80 L2 3.3µH D1 VIN SW SHDN C1 2.2µF R1 28.7k LT1931A C4 68pF C3 4.7µF NFB GND VOUT –5V 200mA R2 10k EFFICIENCY (%) 75 70 65 60 55 C1: TAIYO YUDEN X5R JMK212BJ225MG C2: TAIYO YUDEN X5R LMK212BJ105MG C3: TAIYO YUDEN X5R JMK212BJ475MG D1: ON SEMICONDUCTOR MBR0520 L1, L2: PANASONIC ELJPC3R3MF 50 1931 TA06a 0 50 100 150 200 LOAD CURRENT (mA) 250 1931 TA06b SLIC Power Supply with – 33V and – 68V Outputs, Uses Soft-Start VIN 12V L1 22µH C1 4.7µF 16V VIN R1 1Ω C2 1µF 35V SW D1 RSS 15k VSS LT1931 SHDN 3 2 NFB GND CSS 68nF 1 R2 1k COM C4 4.7µF 35V VOUT1 –33V 100mA* R3 25.5k C6 1000pF R4 2.7k C3 1µF 35V 3 *TOTAL OUTPUT POWER NOT TO EXCEED 3.3W C1 TO C5: X5R OR X7R D1, D2: BAV99 OR EQUIVALENT L1: SUMIDA CR43-220 D2 2 1 C5 4.7µF 35V 1931 TA08 VOUT2 –66V 48mA* 1931fa 10 LT1931/LT1931A U TYPICAL APPLICATIO S SLIC Power Supply with – 21.6V and – 65V Outputs, Uses Soft-Start L1 10µH VIN 5V C1 4.7µF 16V R1 1Ω VIN C2 1µF 35V SW D1 RSS 15k 3 LT1931 SHDN VSS 2 NFB GND 1 VOUT1 –21.6V 48mA* R3 16.2k R2 1k C8 1000pF CSS 68nF COM C5 4.7µF 25V C3 1µF 35V R4 2.7k D2 3 *TOTAL OUTPUT POWER NOT TO EXCEED 1.3W C1 TO C7: X5R OR X7R D1, D2: BAV99 OR EQUIVALENT L1: SUMIDA CR43-100 2 1 C4 1µF 35V C6 4.7µF 25V D3 3 2 1 C7 4.7µF 25V 1931 TA09 VOUT2 – 65V 20mA* 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 3.85 MAX 2.62 REF 1.4 MIN 2.80 BSC 1.50 – 1.75 (NOTE 4) PIN ONE RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR 0.30 – 0.45 TYP 5 PLCS (NOTE 3) 0.95 BSC 0.80 – 0.90 0.20 BSC 0.01 – 0.10 1.00 MAX DATUM ‘A’ 0.30 – 0.50 REF 0.09 – 0.20 (NOTE 3) NOTE: 1. DIMENSIONS ARE IN MILLIMETERS 2. DRAWING NOT TO SCALE 3. DIMENSIONS ARE INCLUSIVE OF PLATING 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 1.90 BSC S5 TSOT-23 0302 REV B 1931fa 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 LT1931/LT1931A U TYPICAL APPLICATIO 2.2MHz, 12V to – 5V Converter Uses Low Profile Coupled Inductor C2 0.1µF L1A 4.7µH VIN 12V L1B 4.7µH D1 VIN SHDN R1 28.7k LT1931A C1 2.2µF VOUT –5V 450mA SW C3 4.7µF NFB GND R2 10k C1: TAIYO YUDEN Y5V EMK212F225ZG C2: 0.1µF 25V X5R C3: TAIYO YUDEN X5R JMK212BJ475MG D1: ON SEMICONDUCTOR MBR0520 L1: SUMIDA CLQ4D10-4R7 DRAWING #5382-T039 1931 TA07a Efficiency 80 EFFICIENCY (%) 75 70 65 60 55 50 0 100 200 300 400 LOAD CURRENT (mA) 500 1931 TA07b RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1307 Single Cell Micropower 600kHz PWM DC/DC Converter 3.3V at 75mA from One Cell, MSOP Package LT1316 Burst ModeTM Operation DC/DC with Programmable Current Limit 1.5V Minimum, Precise Control of Peak Current Limit LT1317 2-Cell Micropower DC/DC with Low-Battery Detector 3.3V at 200mA from Two Cells, 600kHz Fixed Frequency LT1610 Single Cell Micropower DC/DC Converter 3V at 30mA from 1V, 1.7MHz Fixed Frequency LT1611 Inverting 1.4MHz Switching Regulator in 5-Lead ThinSOT –5V at 150mA from 5V Input. Tiny SOT-23 Package LT1613 1.4MHz Switching Regulator in 5-Lead ThinSOT 5V at 200mA from 3.3V Input. Tiny SOT-23 Package LT1615 Micropower Constant Off-Time DC/DC Converter in 5-Lead ThinSOT 20V at 12mA from 2.5V. Tiny SOT-23 Package LT1617 Micropower Inverting DC/DC Converter in 5-Lead ThinSOT –15V at 12mA from 2.5V. Tiny SOT-23 Package LT1930/LT1930A 1.2MHz/2.2MHz, 1A Switching Regulators in 5-Lead ThinSOT 5V at 450mA from 3.3V Input. Tiny SOT-23 Package Burst Mode operation is a trademark of Linear Technology Corporation. 1931fa 12 Linear Technology Corporation LT/LT 1005 REV A • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408)432-1900 ● FAX: (408) 434-0507 ● www.linear-tech.com © LINEAR TECHNOLOGY CORPORATION 2000