Boost Regulators for Battery Powered Applications

August 1996 Application Note 42033 Boost Regulators for Battery Powered Applications INTRODUCTION The incidence of battery powered applications is growing exponentially. One of the most critical parts of the design is the DC-to-DC converter. The wrong choice can degrade battery life or cause the design to become more complex with a large number of external components and higher cost. This application note will highlight the Pulse Frequency Modulation boost regulator choices available, and the key characteristics that each part features. Each of the parts is shown in a typical application circuit, and some waveform and performance data are included. This discussion is limited to the devices with on-chip switches, and it excludes controllers. SINGLE CELL INPUT For purposes of comparison the output current specified for each boost regulator is for a 5 volt output, and for a 1 volt input (or the end of life for most battery chemistries). THE ML4851 — LOW CURRENT, LOW VOLTAGE BOOST REGULATOR The ML4851 is intended for single cell applications requiring less than 25mA of load current, high efficiency, low quiescent current, and a minimum number of external components. It can best be characterized as Micro Linear’s lower output current, lower cost boost IC. The ML4851 includes a low battery detect comparator and is available in two different output versions: a 3.3V output (ML4851-3), and a 5V output (ML4851-5). A typical application circuit is shown in Figure 1. The values used are not optimized for any particular application, but were chosen to give generally acceptable performance over a wide range of operating conditions. To tailor the circuit values for a specific application refer to the data sheet and the following comments: 1. C1 is for evaluation purposes. It provides a bypass for VIN when it is supplied through long wires and high impedance current meters. When a low impedance source is used this value can be reduced. 2. The selection of L1 is critical and determines the performance of the converter. Cost, size, and efficiency are the main parameters to consider when selecting an inductor. See the ML4851 Data Sheet for more information on inductor selection. 3. C2 is optional and may be necessary under certain operating conditions. A ceramic bypass capacitor in the range of 0.1µF is recommended for high ripple conditions. 4. Resistors R1 and R2 are divider resistors for the low battery DETECT input. See the ML4851 Data Sheet for information on calculating their values. VIN GND 7 1 2 3 4 VIN DETECT VREF GND PWR GND RESET R1C1 100µF 10V R2 C2 (op- tional) VL BOOST CONTROL RESET 5 VOUT 8 GND C3 100µF 10V VOUT 6 L1 27µH + Figure 1. Typical Application Circuit Schematic for a ML4851 REV. 1.0 10/25/2000 Application Note 58 2 REV. 1.0 10/25/2000 Figure 2 shows the board layout. The proximity of passive devices and adequate power and ground planes are critical for reliable operation of the circuit. Parts List C1, C3 Capacitor, 100µF, 10V, Tantalum, SMD L1 Inductor, 27µH, 620mA Sumida CD43-270MC U1 ML4851CS-X Vendor List Coilcraft (708) 639-6400 Coiltronics (407) 241-7876 Dale (605) 665-9301 Sumida (708) 956-0667 AVX (207) 282-5111 Matsuo (714) 969-2491 Nemco (415) 571-1234 Sprague (207) 324-4140 Typical Waveforms Typical waveforms are shown in Figures 3 and 4. Figure 3 illustrates a low load condition where the switching frequency is low. Figure 4 illustrates a full load condition. The test conditions are specified below each waveform. Figure 2a. Silk Screen Figure 2b. Top Layer Figure 2c. Bottom Layer Figure 4. Typical switching waveforms — 5V @ 70mA Test Equipment: Tektronix TDS 540 Digitizing Scope Tektronix A6302 Current Probe Tektronix AM503 Current Probe Amp Test Conditions: VIN = 2.4V VOUT = 5V IOUT = 5mA CH1 - VL: 2V/DIV CH2 - IL: 200mA/DIV CH3 - VOUT: 50mV/DIV Horiz: 20µs/DIV Figure 3. Typical switching waveforms — 5V @ 5mA Application Note 58 REV. 1.0 10/25/2000 3 Ef fic ie nc y (% ) IOUT (mA) 90 88 86 84 82 80 78 1 10 100 1000 5V 3.3V VIN = 1V VIN = 2V VIN = 3VVIN = 4V Figure 7: Efficiency vs Output Current Figure 6: No Load Input Current vs Input Voltage 100 95 90 85 80 75 70 65 60 55 50 I O U T (m A ) VIN (V) 1.0 2.0 3.0 5.04.0 5V 3.3V Test Equipment: Tektronix TDS 540 Digitizing Scope Tektronix A6302 Current Probe Tektronix AM503 Current Probe Amp Test Conditions: VIN = 2.4V VOUT = 5V IOUT = 70mA CH1 - VL: 2V/DIV CH2 - IL: 200mA/DIV CH3 - VOUT: 50mV/DIV Horiz: 2µs/DIV Figure 5: Output Current vs Input Voltage 300 250 200 150 100 50 0 I O U T (m A ) VIN (V) 1.0 2.0 3.0 5.04.0 3.3V 5V Performance Data Typical performance curves for the applications circuit are shown in Figures 5, 6, and 7. THE ML4861 – LOW VOLTAGE BOOST REGULATOR The ML4861 is intended for single cell applications requiring more current than the ML4851, but less than 50mA of load current. Although pin compatible with the ML4851, it can best be characterized as Micro Linear’s premium single cell boost IC. The ML4861 includes a low battery detect comparator and is available in three different output versions: a 3.3V output (ML4861-3.3), a 5V output (ML4861-5), and a 6V output (ML4861-6). A typical application circuit is shown in Figure 8. The values used are not optimized for any particular application, but were chosen to give generally acceptable performance over a wide range of operating conditions. To tailor the circuit values for a specific application refer to the ML4861 Data Sheet. Note the following differences in comparison with the ML4851: 1. Larger power switches translates into more output current capability, approximately twice that of the ML4851. 2. Higher cost. 3. Lower ON resistances and therefore a higher switch current rating. 4. Higher switch currents means more output noise. 5. Physically larger inductors required to handle the higher currents. 6. Lower frequency, 10µs ON time versus 5µs for the ML4851. Application Note 58 4 REV. 1.0 10/25/2000 VIN GND 7 1 2 3 4 VIN DETECT VREF GND PWR GND RESET R1*C1 100µF 10V R2*C2 (op- tional) VL BOOST CONTROL RESET 5 VOUT 8 GND C3* VOUT 6 L1 27µH + C4 100 µF 10V *Adjustable (4761) only Figure 8. ML4861 Typical Application Circuit Figure 9 shows the board layout. The proximity of passive devices and adequate power and ground planes are critical for reliable operation of the circuit. Figure 9a. Silk Screen Figure 9b. Top Layer Figure 9c. Bottom Layer Vendor List Coilcraft (708) 639-6400 Coiltronics (407) 241-7876 Dale (605) 665-9301 Matsuo (714) 969-2491 Nemco (415) 571-1234 Sprague (207) 324-4140 Sumida (708) 956-0667 Parts List C1, C4 Capacitor, 100µF, 10V, Tantalum Chip L1 Inductor, 27µH, 1.3A Sumida CD75-270KC U1 ML4861CS-X Application Note 58 REV. 1.0 10/25/2000 5 Typical Waveforms A typical waveform is shown in Figure 10. The test condition is specified below the waveform. 500 400 300 200 100 0 I O U T (m A ) VIN (V) 1.0 2.0 3.0 5.04.0 5V 3.3V 6V 90 85 80 75 70 Ef fic ie nc y (% ) VIN (V) 1.0 2.0 3.0 5.04.0 5V 3.3V 6V Figure 11: Output Current vs Input Voltage Figure 12: Efficiency vs Input Voltage Test Equipment: Tektronix TDS 540 Digitizing Oscilloscope. Test Conditions: VIN = 2.4V VOUT = 5.0V IOUT = 100mA CH1 - VL: 2V/DIV CH2 - VOUT: 100mV/DIV Horiz: 5 µs/div Performance Data Typical performance curves are shown in Figures 11 and 12. Figure 10: Typical Switching Waveforms THE ML4875 - LOW VOLTAGE BOOST REGULATOR WITH SHUTDOWN The ML4875 is a single cell boost intended for applications that require the regulator to shut down. The output current capability is just slightly lower than the ML4861, but the real advantage the ML4875 has is the true shutdown, or load disconnect, feature. The use of a synchronous rectifier allows the ML4875 to break the battery discharge path from the input, through the inductor and rectifier, to the output. Conventional boost circuits that use a Schottky rectifier will always have a discharge path from the input to the output, even though the regulator is shut down. The ML4875 includes a low battery detect comparator and is available in three different output versions: a 3.0V output (ML4875-T), a 3.3V output (ML4875-3), and a 5V output (ML4875-5). A typical application circuit is shown in Figure 13. The values used are not optimized for any particular application, but were chosen to give generally acceptable performance over a wide range of operating conditions. To tailor the circuit values for a specific application refer to the data sheet. Note the following differences in comparison with the ML4851: 1. True shutdown or load disconnect. 2. Larger power switches translates into more output current capability, approximately twice that of the ML4851. 3. Higher cost. 4. Lower ON resistances, and therefore a higher switch current rating. 5. Higher switch currents mean more output noise. 6. Physically larger inductors required to handle the higher currents. 7. Lower frequency: 10µs ON time versus 5µs for the ML4851. Application Note 58 6 REV. 1.0 10/25/2000 VIN GND 7 1 2 3 4 VIN DETECT SHDN GND PWR GND RESET R4* C1 100µF 10V R5* VL BOOST CONTROL RESET 5 VOUT 8 GND C3* VOUT 6 L1 33µH + C2 100 µF 10V *Adjustable (4775) only R1 R2 VREF R3 SHDN Figure 14 shows the board layout. The proximity of passive devices and adequate power and ground planes are critical for reliable operation of the circuit. Vendor List Coilcraft (708) 639-6400 Coiltronics (407) 241-7876 Dale (605) 665-9301 Matsuo (714) 969-2491 Nemco (415) 571-1234 Sprague (207) 324-4140 Sumida (708) 956-0667 Parts List C1, C2 Capacitor, 100µF, 10V, Tantalum SMD L1 Inductor, 33µH, 1.2A Sumida CD75-330 U1 ML4875CS-X Figure 14a. Silk Screen Figure 14b. Top Layer Figure 14c. Bottom Layer Figure 13. ML4875 Typical Application Circuit Application Note 58 REV. 1.0 10/25/2000 7 Typical Waveforms Typical waveforms are shown in Figures 15 and 16. Figure 15 illustrates a low load condition where the switching frequency is low. Figure 16 illustrates a full load condition. The test conditions are specified below each waveform. Test Equipment: Tektronix TDS 540 Digitizing Scope Tektronix A6302 Current Probe Tektronix AM503 Current Probe Amp Test Conditions: VIN = 2.4V VOUT = 5V IOUT = 95mA CH1 - VL: 2V/DIV CH2 - IL: 500mA/DIV CH3 - VOUT: 50mV/DIV Horiz: 5µs/DIV Performance Data Typical performance curves are shown in Figures 17 and 18. Figure 15: Typical Switching Waveforms — 5V @ 5mA Test Equipment: Tektronix TDS 540 Digitizing Scope Tektronix A6302 Current Probe Tektronix AM503 Current Probe Amp Test Conditions: VIN = 2.4V VOUT = 5V IOUT = 5mA CH1 - VL: 2V/DIV CH2 - IL: 500mA/DIV CH3 - VOUT: 50mV/DIV Horiz: 50µs/DIV Figure 16: Typical Switching Waveforms — 5V @ 95mA Figure 18: Efficiency vs Input Voltage 90 85 80 75 Ef fic ie nc y (% ) VIN (V) 1.0 2.0 3.0 5.04.0 3.3V 3.0V 5V 400 350 300 250 200 150 100 50 0 I O U T (m A ) VIN (V) 1.0 2.0 3.0 5.04.0 3.3V 3.0V 5V Figure 17: Output Current vs Input Voltage Application Note 58 8 REV. 1.0 10/25/2000 THE ML4890 - HIGH EFFICIENCY, LOW RIPPLE BOOST REGULATOR The ML4890 is a single cell boost intended for applications that require low ripple. The output current capability is on the order of the ML4851, but the real advantage the ML4890 has is low ripple and a true shutdown feature. By using some of the P-MOS devices from the synchronous rectifier to create a linear regulator the ML4890 has the ability to reduce the output ripple and to break the battery discharge path from the input to the output during shutdown. The ML4890 is available in three different output versions: a 3V output (ML4890-T), a 3.3V output (ML4890-3), and a 5V output (ML4890-5). A typical application circuit is shown in Figure 19. The values used are not optimized for any particular application but were chosen to give generally acceptable performance over a wide range of operating conditions. To tailor the circuit values for a specific application refer to the ML4890 Data Sheet. Note the following differences in comparison with the ML4851: 1. Linear regulator for low output ripple, approximately 5mV. 2. True shutdown or load disconnect. 3. Higher cost. 4. Slightly lower conversion efficiency. Figure 20 shows the board layout. The proximity of passive devices and adequate power and ground planes are critical for reliable operation of the circuit. Figure 19. ML4890 Typical Application Circuit VIN GND 1 2 3 4 VIN VREF GND PWR GND C1 100µF 10V C2 (op- tional) VL 5 VOUT 8 GND VOUT 6 L1 33µH C4 100 µF 10V BOOST CONTROL L D O CONTROL VBOOST SHDN R1 SHDN 7 C3 33µF 16V Figure 20c. Bottom LayerFigure 20b. Top LayerFigure 20a. Silk Screen Application Note 58 REV. 1.0 10/25/2000 9 Parts List C1, C4 Capacitor, 100µF, 10V, Tantalum, SMD C3 Capacitor, 33µF, 16V, Tantalum, SMD R1 Resistor, 510kΩ, 1/8W, 5%, 1206, SMD L1 Inductor, 33µH, 880mA Sumida CD54-330LC U1 ML4890CS-X Vendor List Coilcraft (708) 639-6400 Dale (605) 665-9301 Matsuo (714) 969-2491 Nemco (415) 571-1234 Sumida (708) 956-0667 Typical Waveforms Typical waveforms are shown in Figures 21 and 22. Figure 21 illustrates a low load condition where the switching frequency is low. Figure 22 illustrates a full load condition. The test conditions are specified below each waveform. Test Equipment: Tektronix TDS 540 Digitizing Scope Tektronix A6302 Current Probe Tektronix AM503 Current Probe Amp Test Conditions: VIN = 2.4V VOUT = 5V IOUT = 5mA CH1 - VL: 2V/DIV CH2 - IL: 200mA/DIV CH3 - VOUT: 5mV/DIV Horiz: 50µs/DIV Figure 23: Output Current vs Input Voltage Figure 21: Typical Switching Waveforms — 5V @ 5mA Figure 22: Typical Switching Waveforms — 5V @ 50mA 180 160 140 120 100 80 60 40 20 0 I O U T (m A ) VIN (V) 1.0 2.0 3.0 5.04.0 3.3V 3.0V 5V Test Equipment: Tektronix TDS 540 Digitizing Scope Tektronix A6302 Current Probe Tektronix AM503 Current Probe Amp Test Conditions: VIN = 2.4V VOUT = 5V IOUT = 50mA CH1 - VL: 2V/DIV CH2 - IL: 200mA/DIV CH3 - VOUT: 5mV/DIV Horiz: 5µs/DIV Performance Data Typical performance curves are shown in Figures 23 and 24. Application Note 58 10 REV. 1.0 10/25/2000 Figure 25. ML4868 Typical Application Circuit Schematic VIN GND 7 1 2 3 4 VIN DETECT VREF GND PWR GND RESET R1C1 47µF 10V R2 C2 (op- tional) VL BOOST CONTROL RESET 5 VOUT 8 GND C3 47µF 10V VOUT 6 L1 22µH + MULTIPLE CELL INPUT For purposes of comparison, the output current specified for each boost regulator is for a 2 volt input, or the end of life for most battery chemistries, and for a 5 volt output. THE ML4868 — HIGH FREQUENCY, LOW VOLTAGE BOOST REGULATOR The ML4868 is intended for multiple cell applications requiring low profile components, such as PCMCIA cards. Although pin compatible with the ML4851, and with approximately the same output current capability, it can best be characterized as Micro Linear’s high frequency, multiple cell boost IC. The ML4868 includes a low battery detect comparator and is available in two different output versions: a 3.3V output (ML4868-3), and a 5V output (ML4868-5). A typical application circuit is shown in Figure 25. The values used are not optimized for any particular application, but were chosen to give generally acceptable performance over a wide range of operating conditions. To tailor the circuit values for a specific application refer to the data sheet. Note the following differences in comparison with the ML4851: 1. Higher frequency, 3µs ON time versus 5µs for the ML4851. 2. Higher cost. 3. Lower ON resistances and therefore a higher switch current rating. 4. Physically smaller inductors possible. 90 85 80 75 70 Ef fic ie nc y (% ) VIN (V) 1.0 2.0 3.0 5.04.0 3.3V 3.0V 5V Figure 24: Efficiency vs Input Voltage Application Note 58 REV. 1.0 10/25/2000 11 Parts List C1, C3 Capacitor, 47µF, 10V, Tantalum, SMD L1 Inductor, 22µH, 250mA Murata LQH3C220K04 U1 ML4868CS-X Vendor List Coilcraft (708) 639-6400 Dale (605) 665-9301 Murata (404) 684-7821 Sumida (708) 956-0667 Matsuo (714) 969-2491 Nemco (415) 571-1234 Sprague (207) 324-4140 Typical Waveforms Typical waveforms are shown in Figures 27 and 28. Figure 27 illustrates a low load condition where the switching frequency is low. Figure 28 illustrates a full load condition. The test conditions are specified below each waveform. Test Equipment: Tektronix TDS 540 Digitizing Scope Test Conditions: VIN = 2.4V VOUT = 5V IOUT = 5mA CH1 - VL: 2V/DIV CH2 - IL: 200mA/DIV Horiz: 5µs/DIV Test Equipment: Tektronix TDS 540 Digitizing Scope Test Conditions: VIN = 2.4V VOUT = 5V IOUT = 75mA CH1 - VL: 2V/DIV CH2 - IL: 200mA/DIV Horiz: 2µs/DIV Figure 27: Typical Switching Waveforms — 5V @ 5mA Figure 28: Typical Switching Waveforms — 5V @ 75mA Figure 26a. Silk Screen Figure 26b. Top Layer Figure 26c. Bottom Layer Application Note 58 12 REV. 1.0 10/25/2000 Performance Data Typical performance curves are shown in Figures 29 and 30. VIN GND 7 2 3 4 VIN DETECT GND PWR GND RESET R1 C1 100µF 10V VL2 RESET 5 VOUT 8 GND C2 100µF 10V VOUT 6 L1 10µH VL1 1 BOOST CONTROL R3 Figure 31. ML4871 Typical Application Circuit Schematic 200 180 160 140 120 100 80 60 40 20 0 I O U T (m A ) VIN (V) 1.0 2.0 3.0 5.04.0 3.3V 5V 90 85 80 75 70 65 Ef fic ie nc y (% ) VIN (V) 1.0 2.0 3.0 5.04.0 Figure 30: Efficiency vs Input VoltageFigure 29: Output Current vs Input Voltage values used are not optimized for any particular application but were chosen to give generally acceptable performance over a wide range of operating conditions. To tailor the circuit values for a specific application refer to the ML4871 Data Sheet. Note the following differences in comparison with the ML4851: 1. CCM versus DCM operation. 2. Higher output current capability. 3. Higher cost. 4. Lower ON resistances and therefore a higher switch current rating. 5. Physically small inductors possible. THE ML4871 - HIGH CURRENT BOOST REGULATOR The ML4871 is intended for multiple cell applications requiring more current than the ML4861 can provide. Unlike the previous single cell boost regulators and the ML4868, which always operate in the Discontinuous Conduction Mode, the ML4871 is able to operate in the Continuous Conduction Mode. This CCM operation allows the ML4871 to be characterized as Micro Linear’s high current, multiple cell boost IC. The ML4871 includes a low battery detect comparator, and is available in two different output versions: a 3.3V output (ML4871-3), and a 5V output (ML4871-5). A typical application circuit is shown in Figure 31. The Application Note 58 REV. 1.0 10/25/2000 13 Parts List C1, C2 Capacitor, 100µF, 10V, Tantalum, SMD L1 Inductor, 10µH, 1.44A, 0.1Ω Sumida CD54-100MC U1 ML4871ES-X Vendor List AVX (207) 282-5111 Coilcraft (708) 639-6400 Coiltronics (407) 241-7876 Dale (605) 665-9301 Sumida (708) 956-0667 Sprague (207) 324-4140 Test Equipment: Tektronix TDS 540 Digitizing Scope Test Conditions: VIN = 2.4V VOUT = 5V IOUT = 5mA CH1 - VL: 2V/DIV CH2 - IL: 500mA/DIV CH3 - VOUT: 100mV/DIV Horiz: 10µs/DIV Typical Waveforms Typical waveforms are shown in Figures 33 and 34. Figure 33 illustrates a low load condition where the switching frequency is low. Figure 34 illustrates a full load condition. The test conditions are specified below each waveform. Figure 32a. Top Silk Screen Figure 32b. Top Layer Figure 32c. Bottom Silk Screen Figure 32d. Bottom Layer Figure 33: Typical Switching Waveforms — 5V @ 5mA Application Note 58 14 REV. 1.0 10/25/2000 THE ML487