User's Guide SLUU070 - March 2001 Using the TPS62102 Low-Power High-Efficiency Buck Converter Evaluation Module Kurt Hesse Power Supply Control Products Contents 1 Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2 Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 3 Feedback Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 4 Operating Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 5 Evaluation Module Layouts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 6 Evaluation Module Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 1 SLUU070 1 Features The TPS62102 Low-Power High-Efficiency Buck Converter includes: * 2.5-V to 9-V Input Range * 0.8-V to 8-V Output Range * Dual Auto Mode for High Efficiency at Light Loads * Externally Synchronizable * 0% to 100% Duty Cycle * BICMOS for Low Quiescient, Standby, and Shutdown Currents * 8-Pin SOIC (D) Package 2 Description The TPS62102EVM-01 evaluation module is supplied fully assembled and ready to test. This evaluation module demonstrates an automatic mode switching converter that is capable of 500-mA output current at 3.3 V. The switching frequency of this converter is 1 MHz free running. Other versions of this converter IC are available that have nominal switching frequencies of 300 kHz, 600 kHz, and 2 MHz. Note that the fundamental frequencies have been chosen to minimize interaction with 455-kHz intermediate frequency (IF) circuits. The user needs to supply a power source and suitable load. Figure 1 is the schematic of the evaluation module as assembled. In this configuration, the converter should have a closed-loop bandwidth of approximately 40 kHz. L1 15 H TPS62102 VIN C1 100 F 1 VIN SW VOUT 8 C2 1.0 F D1 MA786CT CB2 2 SD/SYNC 3 MODE PGND 7 FB 6 CB1 GND COMP R6 1k R5 113 k R1 30.1 k 4 C6 10 F C4 1.0 nF R3 0 C8 100 pF 5 R4 35.7 k UDG-00100 Figure 1. Evaluation Module Schematic 2 Using the TPS62102 Low-Power High-Efficiency Buck Converter Evaluation Module SLUU070 This evaluation module allows user control over the SD/SYNC and MODE pins of the TPS62102. As supplied, the MODE (CB1) pin should be left floating. This allows the TPS62102 to automatically determine whether it operates in the continuous frequency mode or in a pulsed frequency modulation (PFM) mode of operation. See the TPS62102 data sheet for details[1]. Phase 100 Gain (dB) 100 Phase (degrees) The SD/SYNC pin is jumpered to ground by default. This allows the TPS62102 to free run. Do not allow this pin to float, as it causes erratic and unpredictable behavior. To synchronize the converter to an external source, connect the source to the middle pin of CB2. The source should pulse its output at a frequency higher than the free running frequency of the converter. Attempting to synchronize to a lower frequency than this results in erratic behavior. The pulse amplitude should be between 2 V and the VIN supplied to the evaluation module. Do not use a pulse amplitude higher than VIN. Minimum pulse width for syncronous signals is 50 ns. This pin can also cause the converter to shut down and enter a low-current mode of operation. To do this, pull the SD/SYNC pin to 2 V or more, and hold it there as long as shutdown is desired. Shutdown occurs approximately 20 s after SD/SYNC is brought high. Gain 0 0 0 100 10k 1M f - Frequency - Hz 100M UDG-00060 Figure 2. Gain/Phase Response for the Internal Error Amplifier Using the TPS62102 Low-Power High-Efficiency Buck Converter Evaluation Module 3 SLUU070 3 Feedback Considerations Figure 2 shows the gain and phase response for the internal error amplifier. In addition to the compensation configuration used, many other feedback configurations are provided for on the evaluation module by using the optional component footprints. Figure 3 shows the schematic of the evaluation module with these additional footprints. As is evident, most any common feedback implementation can be achieved by simply shorting across pads or inserting passive components. The extra footprints are all 1206 size for ease of use. L1 15 H TPS62102 1 C1 100 F CB2 CB1 VIN SW 8 C2 1.0 F 1 2 3 1 2 3 D1 2 SD/SYNC 3 MODE 4 GND PGND 7 FB 6 COMP 5 C6 10 F C7{ R6 1k R1 30.1 k C3{ R5 113 k C4 1.0 nF R3 0 R2{ C8 100 pF C5{ R4 35.7 k UDG-00084 For evaluation use only. Figure 3. Complete Evaluation Module Schematic 3.1 Error Amplifier The error amplifier in this chip has a significant impact on what can be done with the feedback loop. To get a realistic model, assume that the error amplifier has 80 dB (dc) gain, with a 2-MHz GBWP. This may be a bit conservative, but ensures a stable loop if designed with these constraints. 4 Using the TPS62102 Low-Power High-Efficiency Buck Converter Evaluation Module SLUU070 3.2 Open-Loop Small Signal AC Model The circuit of Figure 4 is used to define the feedback loop for this evaluation module. 3.2.1 Specific Open-Loop Signal AC Model Considerations M1 is the lumped gain corresponding to the input voltage and the PWM gain. Since the ramp height in the chip is about 1V the PWM gain is 100%/V or just 1 in the free running case. The 8x factor comes from the input voltage of 8 V. The PWM gain increases with synchronization. For instance, syncronizing a 1-MHz nominal free run oscillator to 1.2 MHz increases the PWM gain to: F G SYNC + SYNC F FREE (1) G FREE Where: * GFREE is the free running PWM gain (1 here) * GSYNC is the synchronized PWM gain * FFREE is the free running oscillator frequency * FSYNC is the synchronized frequency L1 15 H M1 x 8 X CF 10 F RESR 0.01 ac C4 1.0 nF M2 x-1 EAO_1 X R6 1 k R5 113 k C8 100 pF R1 30.1 k R4 36 k EAO + UDG-00085 Figure 4. Open-Loop Small Signal Alternating Current (AC) Model CB1 ADJUSTABLE + POWER SUPPLY - + TB1 CB2 TPS6201X EVM + LOAD TB2 V1 V2 UDG-00104 Figure 5. Connection Diagram Using the TPS62102 Low-Power High-Efficiency Buck Converter Evaluation Module 5 SLUU070 4 Operating Instructions 4.1 Connect a dc Power Supply to Terminal TB1 The power supply should be capable of supplying up to 10 V at 0.5 A. The power supply should be set to its minimum output voltage level and current limited to 0.5 A. 4.2 Connect the Load to TB2 This load should be capable of handling 0.5 A at 3.5 V. 4.3 Place a Jumper on CB2 * Placing the jumper from pin 1 to pin 2 pulls SD/SYNC high, resulting in converter shutdown.* * Placing a jumper from pin 2 to pin 3 pulls SD/SYNC low, resulting in normal operation. 4.3.1 4.4 Placing a jumper on CB1 is optional. * A jumper from pin 1 to pin 2 sets MODE high, forcing the converter into the constant-frequency, heavy-load mode. * A jumper from pin 2 to pin 3 sets MODE low, forcing the converter into the pulsed-variable low power mode. * Letting MODE float, not using a jumper on CB1, allows the converter to operate in auto-mode, the output load detector circuitry determines if the converter should be running in the constant-frequency or pulsed-variable frequency mode. Turn on the Electronic Load Adjust the load to operate between 10 mA and 500 mA. 4.5 Turn on the Input Power Supply Starting with the input dc power supply at its minimum setting, slowly increase the voltage to 7 V 0.5 V. 4.6 Shut Down the Converter To shut down the converter, decrease the dc input power supply voltage to zero. Turn off the electronic load. 6 Using the TPS62102 Low-Power High-Efficiency Buck Converter Evaluation Module SLUU070 5 Evaluation Module Layouts Evaluation module layout examples of the TPS62102EVM-01 PCB are shown in Figure 6 through Figure 8. They are not to scale and appear here only as a reference. Figure 6. Top Layer (top view) Figure 7. Bottom Layer (top view) Using the TPS62102 Low-Power High-Efficiency Buck Converter Evaluation Module 7 SLUU070 Figure 8. Assembly Drawing (top assembly) 6 Evaluation Module Components Table 1. TPS62102EVM-01 Components Description Reference Qty Manufacturer Part Number C1 1 100 F, 20%, 25 V, electrolytic Panasonic-ECG ECE-V1EA101UP C2 1 1.0 F, +80%/-20%, 25 V, ceramic, Y5V Panasonic-ECG ECJ-3YF1E105Z C3, C5, C7 0 For evaluation use only C4 1 1.0 nF, 10%, X7R, 50 V, ceramic Phycomp USA, Inc. 12062R102K9B20D C6 1 10 F, 10%, X7R, 10 V, ceramic Taiyo Yuden LMK325BJ106MN C8 1 100 pF, 5%, 50 V, NPO ceramic Phycomp USA, Inc. 1206CG101J9B200 D1 1 100 mA, Shottky diode Panasonic - SSG MA3X786 Jumpers CB1, CB2 2 100 mil, 3-terminal, strip-line SIP socket Aries Electronics 12-0511-10 Inductors L1 1 15 H, inductor CoilCraft DT1608-153 Resistors R1 1 30.1 k, 1%, metal film resistor, 1/8W Panasonic-ECG ERJ-8ENF3012V R2 0 For evaluation use only R3 1 0 k, 1%, metal film resistor, 1/8W Phycomp USA, Inc. 9C12063A0R00FKHFT R4 1 35.7 k, 1%, metal film resistor, 1/8W Panasonic-ECG ERJ-8ENF3572V R5 1 113 k, 1%, metal film resistor, 1/8W Panasonic-ECG ERJ-8ENF1133V R6 1 1.0 k, 5%, metal film resistor, 1/8W TB1, TB2 2 2-position terminal block connector Weidmuller 171602 U1 1 Low-power synchronous buck controller TI TPS62102DR Capacitors Ca acitors Diodes Terminal Blocks ICs Value/Type Number ERJ-8GEYJ102V Printed circuit board, FR4, 2 oz., n/a SLUP055 2.800" x 1.500" x 0.063" NOTE 1: The values of these components are to be determined by the user in accordance with the application require: PCBs 7 n/a 1 References 1. TPS62102 Low-Power High-Efficiency Buck Converter Data Sheet, Texas Instruments, revised 2000, Literature No. SLUS446. 8 Using the TPS62102 Low-Power High-Efficiency Buck Converter Evaluation Module IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, modifications, enhancements, improvements, and other changes to its products and services at any time and to discontinue any product or service without notice. Customers should obtain the latest relevant information before placing orders and should verify that such information is current and complete. All products are sold subject to TI's terms and conditions of sale supplied at the time of order acknowledgment. TI warrants performance of its hardware products to the specifications applicable at the time of sale in accordance with TI's standard warranty. Testing and other quality control techniques are used to the extent TI deems necessary to support this warranty. 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