TC115 PFM/PWM Step-up DC/DC Converter FEATURES GENERAL DESCRIPTION The TC115 is a high-efficiency step-up DC/DC converter for small, low input voltage or battery powered systems. This device has a guaranteed start-up voltage of 0.9V and a typical supply current of 80 A. Phase compensation and soft-start circuitry are included on-chip. Unlike conventional PWM step-up converters, the TC115 automatically shifts to pulse frequency modulation (PFM) at low loads, resulting in reduced supply current and improved efficiency. The TC115 requires only an external diode, an inductor, and a capacitor, and supports typical output currents of 140 mA. Supply current is reduced to less than 0.5 A, max when SHDN input is brought low. Small size, low installed cost, and low supply current make the TC115 step-up converter ideal for use in a wide range of battery powered systems. High Efficiency at Low Output Load Currents via PFM Mode Space-Saving SOT-89 Package Guaranteed Start-Up at 0.9V 80 A (typ.) Supply Current 85% (typ.) Efficiency at 100 mA 140 mA Typical Output Current @ VIN = 2.0V Low Power Shutdown Mode No External Switching Transistor Needed TYPICAL APPLICATIONS Pagers Cellular Phones Palmtops 1-Cell to 3-Cell Battery Powered Systems Cameras, Video Recorders Local +3V to +5V Supplies ORDERING INFORMATION TYPICAL OPERATING CIRCUITS L1 100 H Sumida CD-54 Part Number D1 +3V OUT 1.5V IN5817 C1 10 F 5 4 GND LX C2 47 F Tantalum Output Osc. Voltage* Freq. (V) Package (KHz) TC115501EMT TC115331EMT TC115301EMT 5.0 3.3 3.0 SOT-89-5 SOT89-5 SOT-89-5 Operating Temp. Range 100 - 40 to +85C 100 - 40 to +85C 100 - 40 to +85C NOTE: *Other output voltages available. Please contact Microchip Technology Inc. for details. TC115 NC PS 1 2 SHDN 3 1.5V to +3V, 50 mA Supply (c) 2001 Microchip Technology Inc. DS21361A TC115-1 4/26/99 PFM/PWM Step-up DC/DC Converter TC115 *Static-sensitive device. Unused devices must be stored in conductive material. Protect devices from static discharge and static fields. Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings only and functional operation of the device at these or any other conditions above those indicated in the operational sections of the specifications is not implied. Exposure to Absolute Maximum Rating Conditions for extended periods may affect device reliability. ABSOLUTE MAXIMUM RATINGS* Power Supply Voltage (PS) .........................................12V Power Dissipation ................................................500 mW LX Sink Current .....................................................400 mA SHDN Input Voltage .................................................... 12V Operating Temperature ............................ -40C to +85C Storage Temperature (TSTG) .................. -40C to +125C ELECTRICAL CHARACTERISTICS: VOUT = 5V; TA = 25C, unless otherwise noted. Circuit Configuration per Figure 1. Symbol Parameter Test Conditions Min Typ Max Unit VIN VSTART ILX(MAX) fLIM VLXLIM IDD ICC 0.9 -- -- -- 0.7 -- -- -- -- -- 200 -- 13 80 10.0 0.9 350 -- 1.3 26 135 V V mA KHz V A A -- 9 17 A -- -- 0.5 A 85 VR x 0.975 -- 10 100 VR KHz V 1.4 17 115 VR x 1.025 2.4 25 80 4 -- -- 0.75 87 10 85 -- -- 92 20 -- 0.2 -- % msec % V V ISD Operating Supply Voltage Start-Up Voltage LX Maximum Sink Current LX Limit Frequency LX Limit Voltage No Load Supply Current Operating Supply Current (Boost Mode) Operating Supply Current (Standby) Shutdown Supply Current VLX = VLXLIM Note 2 IOUT = 0; VIN = VOUT x 0.8 (Note 3) No external components. VIN = (0.95 x VOUT) applied to PS (or VDD) input No external components. VIN = (1.1 x VOUT) applied to PS (or VDD) input SHDN = 0V fOSC VOUT Oscillator Frequency Output Voltage Note 2, Note 4 VIN = 2.2V minimum, Note 1 RSWON PFMDUTY LX Output ON Resistance Duty Cycle, PFM Operating Mode Maximum Duty Cycle Soft Start Time Efficiency SHDN Input Low SHDN Input High VLX = 0.4V No External Components ISTBY MAXDUTY tSS VIH VIL Notes: Note 5 IOUT = 1 mA Note 4 % 1. VR is the nominal factory-programmed output voltage setting. 2. VLXLIM is the voltage on the LX pin (with internal switch ON) that will cause the oscillator to run at twice nominal frequency in to limit the switch current through the internal N-channel switching transistor. 3. Measured with D1 = MA735 (reverse current < 1 A at a reverse voltage of 10V). 4. With TC115 operating in PWM mode. 5. See "Behavior when VIN is greater than the Factory-Programmed VOUT Setting" paragraph under "Detailed Description". TC115-1 4/26/99 2 (c) 2001 Microchip Technology Inc. DS21361A PFM/PWM Step-up DC/DC Converter TC115 PIN DESCRIPTION Pin Number Name 1 2 NC PS 3 SHDN 4 LX 5 GND Description Not Connected. Power and Voltage Sense Input. This dual function input provides both feedback voltage sensing and internal chip power. It should be connected to the regulator output. (See Applications section). Shutdown Input. A logic low on this input suspends device operation and reduces supply current to less than 0.5 A. Device operation resumes when SHDN is brought high. Inductor Switch Output. LX is the drain of an internal N-channel switching transistor. This terminal drives the external inductor, which ultimately provides current to the load. Ground Terminal. PIN CONFIGURATION SOT-89-5 5 4 TC115 1 (c) 2001 Microchip Technology Inc. 2 DS21361A 3 3 TC115-1 4/26/99 PFM/PWM Step-up DC/DC Converter TC115 factory-programmed VOUT setting (VR). Operating the TC115 with VIN > VR causes regulating action to be suspended (and corresponding supply current reduction to 9 A, typical) until VIN is again less than VR. While regulating action is suspended, VIN is connected to VOUT through the series combination of the inductor and Schottky diode. Care must be taken to add the appropriate isolation (MOSFET output switch or post LDO with shutdown) during system design if this VIN/VOUT leakage path is problematic. DETAILED DESCRIPTION The TC115 is a combination PFM/PWM step-up (boost) regulator. It is particularly useful in 1, 2, and 3 cell applications where the required output current is 140 mA or less, and size/cost issues are a concern. The device operates in PWM mode when the output load is sufficient to demand a 10% (or greater) duty cycle. While in PWM mode, the TC115 behaves as any other PWM switching regulator, to a guaranteed maximum duty cycle of 92%. At low output loads (i.e. output loads requiring < 10% duty cycle to support); the TC115 automatically switches to pulse frequency modulation (PFM) operating mode with a fixed duty cycle of 25%, max, (17%, typical). While in PFM mode, the inductor is modulated with individual fixed width pulses only as needed to maintain output voltage. This action reduces supply current, thereby improving power efficiency at low output loads. VIN + C1 L1 D1 VOUT C2 5 + 4 LX GND TC115 Input Power and Sensing The TC115 is powered from the PS input, which must be connected to the regulated output as shown in Figure 1. PS also senses output voltage for closed-loop regulation. Startup current is furnished through the inductor when input voltage is initially applied. This action starts the oscillator, causing the voltage at the PS input to rise, bootstrapping the regulator into full operation. NC PS 1 2 SHDN 3 OFF ON (Tie to VIN or VOUT if not used) Figure 1. TC115 Typical Application Output Diode APPLICATIONS Input Bypass Capacitors For best results, use a Schottky diode such as the MA735, 1N5817, EC10 or equivalent. Connect the diode between the PS and LX pins as close to the IC as possible. Do not use ordinary rectifier diodes since the higher threshold voltages reduce efficiency. Adding an input bypass capacitor reduces peak current transients drawn from the input supply, and reduces the switching noise generated by the regulator. The source impedance of the input supply determines the size of the capacitor that should be used. Low Power Shutdown Mode The TC115 enters a low power shutdown mode when SHDN is brought low. While in shutdown, the oscillator is disabled and the internal switch is shut off. Normal regulator operation resumes when SHDN is brought high. SHDN may be tied to the input supply if not used. Note: Because the TC115 uses an external diode, a leakage path between the input voltage and the output node (through the inductor and diode) exists while the regulator is in shutdown. Care must be taken in system design to assure the input supply is isolated from the load during shutdown. Inductor Selection Selecting the proper inductor value is a trade-off between physical size and power conversion requirements. Lower value inductors cost less, but result in higher ripple current and core losses. They are also more prone to saturate since the coil current ramps to a higher value. Larger inductor values reduce both ripple current and core losses, but are larger in physical size and tend to increse the start-up time slightly. Practical inductor values, therefore, range from 50 H to 300 H. Inductors with a ferrite core (or equivalent) are recommended. For highest efficiency, use an inductor with a series resistance less than 20 m. Behavior When VIN is Greater Than the Factory-Programmed VOUT Setting The TC115 is designed to operate as a step-up regulator only. As such, VIN is assumed to always be less than the TC115-1 4/26/99 4 (c) 2001 Microchip Technology Inc. DS21361A PFM/PWM Step-up DC/DC Converter TC115 Solving for input curent: The inductor value directly affects the output ripple voltage. Equation 3 is derived as shown below, and can be used to calculate an inductor value, given the required output ripple voltage (VRIPPLE) and output capacitor series resistance: IIN(MAX) = Equation 6. VRIPPLE ESR(di) The sawtooth current is centered on the DC current level; swinging equally above and below the DC current calculated in Equation 6. The peak inductor current is the sum of the DC current plus half the AC current. Note that minimum input voltage should be used when calculating the AC inductor current (Equation 9). Equation 1. where ESR is the equivalent series resistance of the output filter capacitor, and VRIPPLE is in volts. Expressing di in terms of switch ON resistance and time: V = L(di) dt ESR [(VIN - VSW)tON] L VRIPPLE (VOUT(MAX))(IOUT(MAX)) (Efficiency)(VIN(MIN)) Equation 7. Equation 2. di = Solving for L: V(dt) L Equation 8. L ESR [(VIN - VSW)tON] VRIPPLE di = Equation 3. [(VIN(MIN) - VSW)tON] L Equation 9. Care must be taken to ensure the inductor can handle peak switching currents, which can be several times load currents. Exceeding rated peak current will result in core saturation and loss of inductance. The inductor should be selected to withstand currents greater than IPK (Equation 10) without saturating. Calculating the peak inductor current is straightforward. Inductor current consists of an AC (sawtooth) current centered on an average DC current (i.e. input current). Equation 6 calculates the average DC current. Note that minimum input voltage and maximum load current values should be used: where: VSW = VCESAT of the switch (note if a CMOS switch is used to substitute VCESAT with RDSON x IIN) Combining the DC current calculated in Equation 6, with half the peak AC current calculated in Equation 9, the peak inductor current is given by: IPK = IIN(MAX) + 0.5(di) Equation 10. Internal Transistor Switch Input Power = Output Power Efficiency The LX pin has a typical ON resistance of 1.4, therefore peak switch current is given by (VIN/1.4). The internal transistor switch has a maximum design rating of 350 mA. An oscillator frequency doubling circuit is an included guard against high switching currents. Should the voltage on the LX pin rise above 1.3V, max, while the internal N-channel switch is ON, the oscillator frequency automatically doubles to minimize ON time. Although reduced, switch current still flows because the PWM remains in operation. Therefore, the LX input is not internally current limited and care must be taken never to exceed the 350 mA maximum limit. Failure to observe this will result in damage to the regulator. Equation 4. Re-writing in terms of input and output currents and voltages: (VIN(MIN)) (IN(MAX)) = (VOUT(MAX))(IOUT(MAX)) Efficiency Equation 5. (c) 2001 Microchip Technology Inc. DS21361A 5 TC115-1 4/26/99 PFM/PWM Step-up DC/DC Converter TC115 Output Capacitor Board Layout Guidelines The effective series resistance of the output capacitor directly affects the amplitude of the output voltage ripple. (The product of the peak inductor current and the ESR determines output ripple amplitude.) Therefore, a capacitor with the lowest possible ESR should be selected. Smaller capacitors are acceptable for light loads or in applications where ripple is not a concern. The Sprague 595D series of tantalum capacitors are amongst the smallest of all low ESR surface mount capacitors available. Table 1 lists suggested component numbers and manufacturers. As with all inductive switching regulators, the TC115 generates fast switching waveforms which radiate noise. Interconnecting lead lengths should be minimized to keep stray capacitance, trace resistance and radiated noise as low as possible. In addition, the GND pin, input bypass capacitor and output filter capacitor ground leads should be connected to a single point. The input capacitor should be placed as close to power and ground pins of the TC115 as possible. Table 1. Suggested Components and Manufacturers Type Inductors Capacitors Diodes Surface Mount Sumida CD54 Series CDR125 Series Matsuo 267 Series Nihon EC10 Series Sprague 595D Sreies Matshushita MA735 Series Nichicon F93 Series Sanyo OS-CON Series Motorola 1N5817 - 1N5822 Coiltronics CTX Series Through Hole Sumida RCH855 Series RCH110 Series Nichicon PL Series Renco RL1284-12 TC115-1 4/26/99 6 (c) 2001 Microchip Technology Inc. DS21361A PFM/PWM Step-up DC/DC Converter TC115 The TC115DEMO is shipped with the TC115 installed, and separate Schottky diode, Coiltronics 100 H inductor, and 47F tantalum capacitor. Two sets of mounting holes are supplied for the inductor to accommodate values from 20H to 100H. The regulator is shut down when J1 terminal X is shorted to OFF, and operates normally when J1 terminal X is shorted to ON. Terminal Y (J2) must be connected to BS. TC115 DEMO CARD The TC115 DEMO Card is a 1.5" x 0.9" card containing a TC115 with sites for the through-hole inductor, Schottky diode, and input and output capacitors. It supports both bootstrapped and non-bootstrapped converter operating modes. These cards are available from your local TelCom Semiconductor sales office. VOUT VIN COUT TC115-0 L1 CIN J1 TC115 GND J2 OFF X ON BS Y NB Full Size Component Side of Board Figure 2. TC115 Demo Board Layout D1 VIN VOUT L1 + + CIN COUT 4 5 GND LX TC115 NC PS 1 2 SHDN 3 NB Y BS J2 Bootstrap/ Non-Bootstrap ON X OFF J1 Shutdown Control Figure 3. TC115 Demo Schematic (c) 2001 Microchip Technology Inc. DS21361A 7 TC115-1 4/26/99 PFM/PWM Step-up DC/DC Converter TC115 TYPICAL RIPPLE WAVEFORMS TC115301 VIN = 1.0V ILOAD = 10 mA CH1: VOUT (DC) CH2: VOUT (AC Ripple) L = 100H C = 47F D1 = MA735 TC115301 VIN = 2.0V ILOAD = 40mA CH1: VOUT (DC) CH2: VOUT (AC Ripple) L = 100H C = 47F D1 = MA735 TC115301 VIN = 2.5V ILOAD = 80mA CH1: VOUT (DC) CH2: VOUT (AC Ripple) L = 100H C = 47F D1 = MA735 TC115-1 4/26/99 8 (c) 2001 Microchip Technology Inc. DS21361A PFM/PWM Step-up DC/DC Converter TC115 TYPICAL CHARACTERISTICS CURVES TC115301EMT TC115301EMT OUTPUT VOLTAGE vs. OUTPUT CURRENT EFFICIENCY vs. OUTPUT CURRENT 100 80 2.9 EFFICIENCY (%) OUTPUT VOLTAGE VOUT (V) 3.1 2.0V VIN = 1.0V 1.5V 2.7 2.0V 60 VIN = 1.0V 40 1.5V 20 L1 = 100H C2 = 47F (Tantalum) 2.5 0 40 80 120 L1 = 100H C2 = 47F (Tantalum) 160 0 200 0 OUTPUT CURRENT IOUT (mA) 40 80 120 160 200 OUTPUT CURRENT IOUT (mA) TC115301EMT TC115301EMT NO LOAD INPUT CURRENT vs. INPUT VOLTAGE RIPPLE VOLTAGE vs. OUTPUT CURRENT 200 100 RIPPLE VOLTAGE: Vr(mVp-p) INPUT CURRENT IIN (A) L1 = 100H C2 = 47F (Tantalum) 150 100 50 0 1.0 80 60 2.0V 1.5V VIN = 1.0V 40 10 0 1.2 1.4 1.6 1.8 0 2.0 INPUT VOLTAGE VIN (V) (c) 2001 Microchip Technology Inc. L1 = 100H C2 = 47F (Tantalum) DS21361A 9 40 80 120 160 OUTPUT CURRENT IOUT (mA) 200 TC115-1 4/26/99 PFM/PWM Step-up DC/DC Converter TC115 represents 1st decimal of voltage and frequency MARKINGS SOT-89-5 Symbol 100KHz 0 1 2 3 4 5 6 7 8 9 represents product classification; TC115 = 1 represents 1st integer of voltage and frequency Output Voltage .0 .1 .2 .3 .4 .5 .6 .7 .8 .9 represents lot ID number Symbol 100KHz 1 2 3 4 5 6 Output Voltage 1. 2. 3. 4. 5. 6. Example: For TC115331, the marking code is 3 X 1 3 TAPING FORM Component Taping Orientation for 5-Pin SOT-89 Devices PIN 1 User Direction of Feed User Direction of Feed Device Marking Device Marking W PIN 1 P Standard Reel Component Orientation TR Suffix Device (Mark Right Side Up) Reverse Reel Component Orientation RT Suffix Device (Mark Upside Down) Carrier Tape, Number of Components Per Reel and Reel Size Package Carrier Width (W) Pitch (P) Part Per Full Reel Reel Size 12 mm 8 mm 1000 7 in 5-Pin SOT-89 Package 5L SOT-89 TC115-1 4/26/99 Carrier Width (W) Pitch (P) Part Per Full Reel Reel Size 12 mm 8 mm 1000 7 10 (c) 2001 Microchip Technology Inc. DS21361A PFM/PWM Step-up DC/DC Converter TC115 PACKAGE DIMENSIONS 5-Pin SOT-89 .181 (4.60) .173 (4.40) .071 (1.80) .055 (1.40) .063 (1.60) .055 (1.40) .016 (0.40) REF. .019 (0.48) .014 (0.32) .102 (2.60) .177 (4.50) MAX. .094 (2.40) PIN 1 .031 (0.80) MIN. .021 (0.53) .016 (0.41) .017 (0.44) .014 (0.37) .063 (1.60) .055 (1.40) .019 (0.48) .014 (0.36) Dimensions: inches (mm) (c) 2001 Microchip Technology Inc. DS21361A 11 TC115-1 4/26/99 PFM/PWM Step-up DC/DC Converter TC115 WORLDWIDE SALES AND SERVICE AMERICAS New York Corporate Office 150 Motor Parkway, Suite 202 Hauppauge, NY 11788 Tel: 631-273-5305 Fax: 631-273-5335 2355 West Chandler Blvd. Chandler, AZ 85224-6199 Tel: 480-792-7200 Fax: 480-792-7277 Technical Support: 480-792-7627 Web Address: http://www.microchip.com Rocky Mountain 2355 West Chandler Blvd. Chandler, AZ 85224-6199 Tel: 480-792-7966 Fax: 480-792-7456 ASIA/PACIFIC (continued) San Jose Microchip Technology Inc. 2107 North First Street, Suite 590 San Jose, CA 95131 Tel: 408-436-7950 Fax: 408-436-7955 Singapore Microchip Technology Singapore Pte Ltd. 200 Middle Road #07-02 Prime Centre Singapore, 188980 Tel: 65-334-8870 Fax: 65-334-8850 Taiwan Atlanta 6285 Northam Drive, Suite 108 Mississauga, Ontario L4V 1X5, Canada Tel: 905-673-0699 Fax: 905-673-6509 500 Sugar Mill Road, Suite 200B Atlanta, GA 30350 Tel: 770-640-0034 Fax: 770-640-0307 Microchip Technology Taiwan 11F-3, No. 207 Tung Hua North Road Taipei, 105, Taiwan Tel: 886-2-2717-7175 Fax: 886-2-2545-0139 ASIA/PACIFIC Austin EUROPE China - Beijing Australia Analog Product Sales 8303 MoPac Expressway North Suite A-201 Austin, TX 78759 Tel: 512-345-2030 Fax: 512-345-6085 Boston 2 Lan Drive, Suite 120 Westford, MA 01886 Tel: 978-692-3848 Fax: 978-692-3821 Boston Analog Product Sales Unit A-8-1 Millbrook Tarry Condominium 97 Lowell Road Concord, MA 01742 Tel: 978-371-6400 Fax: 978-371-0050 Toronto Microchip Technology Beijing Office Unit 915 New China Hong Kong Manhattan Bldg. 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No licenses are conveyed, implicitly or otherwise, except as maybe explicitly expressed herein, under any intellectual property rights. The Microchip logo and name are registered trademarks of Microchip Technology Inc. in the U.S.A. and other countries. All rights reserved. All other trademarks mentioned herein are the property of their respective companies. TC115-1 4/26/99 12 (c) 2001 Microchip Technology Inc. DS21361A