TC105303ECT

TC105 PFM/PWM Step-Down DC/DC Controller Features 57µA (Typ) Supply Current 1A Output Current 0.5µA Shutdown Mode 300kHz Switching Frequency for Small Inductor Size • Programmable Soft-Start • 92% Typical Efficiency • Small Package: 5-Pin SOT-23A • • • • Package Type 5-Pin SOT-23A VOUT 5 SHDN 4 TC105 1 EXT 2 VDD 3 GND Applications • • • • • • • Palmtops Battery-Operated Systems Portable Instruments Positive LCD Bias Generators Portable Communicators Hand-Held Scanners 5V to 3V Down Converters NOTE: 5-Pin SOT-23A is equivalent to the EIAJ SC-74A General Description The TC105 is a step-down (Buck) switching controller that furnishes output currents of up to 1A (max) while delivering a typical efficiency of 92%. The TC105 normally operates in pulse width modulation mode (PWM), but automatically switches to pulse frequency modulation (PFM) at low output loads for greater efficiency. Oscillator frequency is 300kHz, allowing use of small (22µH) inductors. Supply current draw is only 102µA (max), and is reduced to less than 0.5µA when the SHDN input is brought low. Regulator operation is suspended during shutdown. The TC105 accepts a maximum input voltage of 10V. The TC105 is available in a small 5-Pin SOT-23A package, occupies minimum board space and is ideal for a wide range of applications. Device Selection Table Part Number TC105503ECT TC105333ECT TC105303ECT Output Voltage (V)* 5.0 3.3 3.0 Package 5-Pin SOT-23A 5-Pin SOT-23A 5-Pin SOT-23A Osc. Freq. (kHz) 300 300 300 Operating Temp. Range -40°C to +85°C -40°C to +85°C -40°C to +85°C *Other output voltages are available. Please contact Microchip Technology Inc. for details. Functional Block Diagram L1 22µH (Sumida CD54) RSS 470K D1 MA737 CSS 0.033µF 3.3V VOUT OFF ON (From System Control Logic) 5 VOUT 4 SHDN C2 47µF 10V Tantalum TC105333ECT EXT VDD GND 1 2 3 Si 9430 P + VBATT 6V – NiMH C1 10µF/16V 3.3V Regulated Supply Using 6V NiMH Batter y Pack Input 2002 Microchip Technology Inc. DS21349B-page 1 © TC105 1.0 ELECTRICAL CHARACTERISTICS Absolute Maximum Ratings* Voltage on VDD ....................................... -0.3V to +12V EXT Output Current ........................................±100mA Voltage on VOUT, EXT, SHDN Pins .....................................-0.3V to VDD +0.3V Power Dissipation.............................................150mW Operating Temperature Range............. -40°C to +85°C Storage Temperature Range .............. -40°C to +125°C *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 operation sections of the specifications is not implied. Exposure to Absolute Maximum Rating conditions for extended periods may affect device reliability. TC105 ELECTRICAL SPECIFICATIONS Electrical Characteristics: Note 1, fOSC = 300 kHz; TA = 25°C, unless otherwise noted. Symbol VDD VDD MIN IDD ISTBY ISHDN fOSC VOUT Parameter Operating Supply Voltage Minimum Input Voltage Operating Supply Current Standby Supply Current Shutdown Supply Current Oscillator Frequency Output Voltage Min 2.2 0.9 — — — — — 255 VR x 0.975 100 15 0.65 — — — — — — — — Typ — — 57 67 15 16 — 300 VR — 25 — — 17 16 12 15 14 10 92 Max 10.0 2.2 102 122 27 29 0.5 345 VR x 1.025 — 35 — 0.20 24 22 17 20 19 14 — % % V V Ω IOUT = 0mA VOUT = 0V, No external components VOUT = 0V, No external components No external components; VR = 3.0V VR = 3.3V VR = 5.0V VOUT = SHDN = VIN , VEXT = (VIN – 0.4V) No external components; VR = 3.0V VR = 3.3V VR = 5.0V VOUT = 0V, SHDN = VIN, VEXT = 0.4V Units V V µA µA µA kHz EXT = High; No external components; VOUT = 0V, SHDN = VIN No external components; VR = 3.0V, 3.3V VOUT = 0V, SHDN = VIN VR = 5.0V No external components; VR = 3.0V, 3.3V VOUT = SHDN = VIN VR = 5.0V SHDN = GND VIN = VOUT + 0.3V Note 2 Test Conditions DTYMAX Maximum Duty Cycle (PWM Mode) DTYPFM Duty Cycle (PFM Mode) VIH VIL REXTH SHDN Input Logic High SHDN Input Logic Low EXT ON Resistance to VDD REXTL EXT ON Resistance to GND Ω η Note 1: Efficiency VR = 3.0V, VIN = 4.5V, IOUT = 200mA VR = 3.3V, VIN = 5.0V, IOUT = 220mA VR = 5.0V, VIN = 7.5V, IOUT = 320mA VR is the factory output voltage setting. % 2: © DS21349B-page 2 2002 Microchip Technology Inc. TC105 2.0 PIN DESCRIPTIONS The descriptions of the pins are listed in Table 2-1. TABLE 2-1: Pin No. (5-Pin SOT-23A) 1 2 3 4 PIN FUNCTION TABLE Symbol EXT VDD GND SHDN Description Switch transistor control output. This terminal connects to the gate of an external P-channel MOSFET (or to the base of an external PNP transistor through a current limiting resistor). Power supply voltage input. Ground terminal. Shutdown input (active low). The device enters a low power shutdown state when this input is brought low. During shutdown, regulator action is suspended, and supply current is reduced to less than 0.5µA. The device resumes normal operation when SHDN is again brought high. Voltage sense input. This input senses output voltage for regulation and must be connected to the output voltage node as shown in the application schematic in this data sheet. 5 VOUT 2002 Microchip Technology Inc. DS21349B-page 3 © TC105 3.0 DETAILED DESCRIPTION 3.4 Input Bypass Capacitors The TC105 is a PFM/PWM step-down DC/DC controller for use in systems operating from two or more cells, or in line-powered applications. It uses PWM as the primary modulation scheme, but automatically converts to PFM at output duty cycles less than approximately 10%. The conversion to PFM provides reduced supply current, and therefore higher operating efficiency at low loads. The TC105 uses an external switching transistor, allowing construction of switching regulators with output currents of up to 1A. The TC105 consumes only 102µA, max, of supply current when VIN = 5V and VOUT = 3.3V, and can be placed in a 0.5µA shutdown mode by bringing the shutdown input (SHDN) low. The regulator remains disabled while in shutdown mode, and output voltage discharges to zero through the load. Normal operation resumes when SHDN is brought high. Other features include a built-in undervoltage lockout (UVLO) and externally programmable soft start time. Using 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. 3.5 Output Capacitor 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 among the smallest of all low ESR surface mount capacitors available. Table 4-1 lists suggested components and suppliers. 3.1 Low Power Shutdown Mode 3.6 Inductor Selection The TC105 enters a low power shutdown mode when SHDN is brought low. While in shutdown, the oscillator is disabled and the output switch is shut off. Normal regulator operation resumes when SHDN is again brought high. SHDN may be tied to the input supply if not used. 3.2 Soft Start Soft start allows the output voltage to gradually ramp from 0 to rated output value during start-up. This action minimizes (or eliminates) overshoot, and in general, reduces stress on circuit components. Figure 4-1 shows the circuit required to implement soft start (values of 470K and 0.033µF for R SS and CSS respectively, are adequate for most applications). 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 faster and could overshoot the desired peak value. This not only reduces efficiency, but could also cause the current rating of the external components to be exceeded. Larger inductor values reduce both ripple current and core losses, but are larger in physical size and tend to increase the start-up time slightly. A 22µH inductor is recommended as the best overall compromise. For highest efficiency, use inductors with a low DC resistance (less than 20 mΩ). To minimize radiated noise, consider using a toroid, pot core or shielded-bobbin inductor. 3.3 Undervoltage Lockout (UVLO) 3.7 Output Diode The TC105 is disabled when VIN is below the undervoltage lockout threshold. This threshold is equal to the guaranteed minimum operating voltage for the TC105 (i.e., 2.2V). When UVLO is active, the TC105 is completely disabled. The high operating frequency of the TC105 requires a high-speed diode. Schottky diodes such as the MA737 or 1N5817 through 1N5823 (and the equivalent surface mount versions) are recommended. Select a diode whose average current rating is greater than the peak inductor current and whose voltage rating is higher than VDDMAX. © DS21349B-page 4 2002 Microchip Technology Inc. TC105 3.8 External Switching Transistor Selection 3.8.1 BOARD LAYOUT GUIDELINES As with all inductive switching regulators, the TC105 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 TC105 as possible. The length of the EXT trace must also be kept as short as possible. EXT is a complementary output with a maximum ON resistance of 22Ω to V DD when high and 19Ω to ground when low. It is designed to directly drive a P-channel MOSFET or a PNP bipolar transistor through a base current limiting resistor (Figure 4-2). A PNP transistor is recommended in applications where VIN is less than 2.5V. Otherwise, a P-channel MOSFET is preferred as it affords the highest efficiency because it does not draw any gate drive current. However, P-channel MOSFETs are typically more expensive than bipolar transistors. P-channel MOSFET selection is determined mainly by the on-resistance, gate-source threshold, and gate charge requirements. Also, the drain-to-source and gate-to-source breakdown voltage ratings must be greater than VDDMAX. The total gate charge specification should be less than 100nC for best efficiency. The MOSFET must be capable of handling the required peak inductor current, and should have a very low on-resistance at that current. For example, an Si9430 MOSFET has a drain-to-source rating of -20V, and a typical on-resistance rDSON of 0.07Ω at 2A, with VGS = -4.5V. Table 4-1 lists suppliers of external components recommended for use with the TC105. 2002 Microchip Technology Inc. DS21349B-page 5 © TC105 4.0 4.1 APPLICATIONS Circuit Examples FIGURE 4-1: SOFT START CIRCUIT RSS 470K + 4 SHDN/SS Figure 4-3 shows a TC105 using a PNP switching transistor (Zetex FZT749) that has an hFE of 180 and VCESAT of 100 mV at IC = 1A. Other high beta transistors can be used, but the values of RB and CB may need adjustment if hFE is significantly different from that of the FZT749. The circuit of Figure 4-4 utilizes a P-channel MOSFET switching transistor (Silconix Si9430). This transistor is a member of the Littlefoot™ family of small outline MOSFETs. VIN CSS 0.033µF – TC105 Shutdown Not Used RSS 470K SHDN + CSS 0.033µF OFF ON (From System Control Logic) 4 SHDN/SS – TC105 Shutdown Used FIGURE 4-2: VIN P EXTERNAL TRANSISTOR CONNECTION L D + – VOUT CL VIN Q + D – CL L VOUT TC105 EXT 1 RB + – CB TC105 EXT 1 P-Channel MOSFET PNP Bipolar Transistor © DS21349B-page 6 2002 Microchip Technology Inc. TC105 FIGURE 4-3: REGULATOR USING PNP TRANSISTOR FZ749 Q1 10µF 16V – 22µH Sumida CD-54 VIN 2.5V + + MA737 – 47µF 10V Tantalum VOUT 1.8V RSS 470K OFF ON 5 VOUT CB 2200 pF – 4 SHDN/SS + – CSS 0.033µF + RB 500 EXT 1 TC105 VDD 2 GND 3 FIGURE 4-4: REGULATOR USING P-CHANNEL MOSFET Si9430 P VIN 10µF 16V – 22µH Sumida CD-54 + + MA737 – 47µF 10V Tantalum VOUT RSS 470K OFF ON CSS 0.033µF + 5 VOUT 4 SHDN/SS – TC105 EXT 1 VDD 2 GND 3 TABLE 4-1: Type Surface Mount SUGGESTED COMPONENTS AND SUPPLIERS Inductors Sumida CD54 Series CDRH Series Coilcraft DO Series Capacitors AVX TPS Series Sprague 595D Series Diodes ON Semiconductor MBRS340T3 Nihon NSQ Series Matsushita MA737 Sanyo OS-CON Series Nichicon PL Series United Chemi-Con LXF Series IRC OAR Series ON Semiconductor TMOS Power MOSFETs (i.e., MTP30P06V) Transistors Silconix Little Foot MOSFET Series Zetex FZT749 PNP Bipolar Transistor Toshiba 2SA1213 PNP Transistor Miniature Through-Hole Standard Through-Hole Sumida RCH Series Coilcraft PCH Series Coiltronics CTX Series 2002 Microchip Technology Inc. DS21349B-page 7 © TC105 5.0 5.1 PACKAGING INFORMATION Package Marking Information 3 represents first decimal of voltage Symbol (300kHz) A B C D E F H K L M Voltage .0 .1 .2 .3 .4 .5 .6 .7 .8 .9 1 represents product classification; TC105 = M represents first integer of voltage Symbol (300kHz) 1 2 3 4 5 6 Voltage 1. 2. 3. 4. 5. 6. 2 4 represents production lot ID code © DS21349B-page 8 2002 Microchip Technology Inc. TC105 5.2 Taping Form Component Taping Orientation for 5-Pin SOT-23A (EIAJ SC-74A) Devices User Direction of Feed Device Marking W PIN 1 P Standard Reel Component Orientation TR Suffix Device (Mark Right Side Up) Carrier Tape, Number of Components Per Reel and Reel Size Package Carrier Width (W) Pitch (P) Part Per Full Reel Reel Size 5-Pin SOT-23A 8 mm 4 mm 3000 7 in 5.3 Package Dimensions SOT-23A-5 .075 (1.90) REF. .122 (3.10) .098 (2.50) .020 (0.50) .012 (0.30) PIN 1 .122 (3.10) .106 (2.70) .057 (1.45) .035 (0.90) .006 (0.15) .000 (0.00) .071 (1.80) .059 (1.50) .037 (0.95) REF. 10° MAX. .024 (0.60) .004 (0.10) .010 (0.25) .004 (0.09) Dimensions: inches (mm) 2002 Microchip Technology Inc. DS21349B-page 9 © TC105 NOTES: © DS21349B-page 10 2002 Microchip Technology Inc. TC105 Sales and Support Data Sheets Products supported by a preliminary Data Sheet may have an errata sheet describing minor operational differences and recommended workarounds. To determine if an errata sheet exists for a particular device, please contact one of the following: 1. 2. 3. Your local Microchip sales office The Microchip Corporate Literature Center U.S. FAX: (480) 792-7277 The Microchip Worldwide Site (www.microchip.com) Please specify which device, revision of silicon and Data Sheet (include Literature #) you are using. New Customer Notification System Register on our web site (www.microchip.com/cn) to receive the most current information on our products.  2002 Microchip Technology Inc. DS21349B-page11 TC105 NOTES: DS21349B-page12  2002 Microchip Technology Inc. TC105 Information contained in this publication regarding device applications and the like is intended through suggestion only and may be superseded by updates. It is your responsibility to ensure that your application meets with your specifications. No representation or warranty is given and no liability is assumed by Microchip Technology Incorporated with respect to the accuracy or use of such information, or infringement of patents or other intellectual property rights arising from such use or otherwise. Use of Microchip’s products as critical components in life support systems is not authorized except with express written approval by Microchip. No licenses are conveyed, implicitly or otherwise, under any intellectual property rights. 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