LTC3440 JMK212BJ106MG JMK325BJ226MM CDRH4D28-100 DN275 JMK212BJ106MM MBRM120T3

Single Inductor, Tiny Buck-Boost Converter Provides 95% Efficiency in Lithium-Ion to 3.3V Applications Design Note 275 Mark

advertisement Single Inductor, Tiny Buck-Boost Converter Provides 95% Efficiency in Lithium-Ion to 3.3V Applications Design Note 275 Mark Jordan Introduction In portable applications powered by a single lithium-ion cell, the input voltage can typically change from 4.2V initially, down to 2.5V at end of life. It is a challenging task to provide a regulated voltage within the range of the battery. Until now, the most popular solution has been the SEPIC converter, but its mediocre efficiency and requirement of both a coupled inductor and a high current flyback capacitor make it a less than optimal solution. Another option is to cascade a Boost converter with either an LDO or a Buck converter, but the additional area and cost of the extra components, as well as low efficiency, are major drawbacks. Linear Technology's new LTC®3440 BuckBoost converter provides the most compact solution with the highest efficiency, thereby reducing cost, increasing battery life and saving precious real estate. offers user controlled Burst Mode® operation to maximize battery life, drawing only 25µA of quiescent current. The operating frequency can be programmed from 300KHz to 2MHz by changing the value of the timing resistor on the RT pin. Users can synchronize the operating frequency by connecting an external clock to the MODE/ SYNC pin. The part can also be commanded to shut down by pulling the SHDN/SS pin low. In shutdown, the part draws less than 1µA of quiescent current and disconnects the output from the input supply. During start-up, the ramp rate of the output voltage is controlled by the external soft-start components. This controlled ramp rate provides for inrush current limiting. Housed in a thermally enhanced 10-lead MSOP package, the LTC3440 LTC3440 is ideal for portable power applications requiring less than 2W of output power. The LTC3440 LTC3440 incorporates a patent-pending control technique to efficiently regulate an output voltage above, below or equal to the input source voltage with a single inductor by properly phasing the four internal switches. Efficiencies well over 90% are achieved for the entire battery range without the use of Schottky rectifier diodes. The low RDS(ON) (0.19 NMOS, 0.22 PMOS), low gate charge synchronous switches, along with minimal breakbefore-make times, provide high frequency, low noise operation with high efficiency. For light loads, the part All Ceramic Capacitor, Single Inductor, 2W Li-Ion to 3.3V Converter An all-ceramic capacitor, lithium-ion to 3.3V application at 600mA is shown in Figure 1. The operating frequency is programmed to 1MHz and soft-start is incorporated with R4 and C3. The efficiency curves versus load current for the Li-Ion battery range are shown in Figure 2. With Burst Mode operation enabled at light loads, efficiencies 100 L1 10µH VOUT 3.3V 600mA R4 1M Li-Ion 8 + 2 C3 0.1µF C1 10µF SD R5 1k * 1 RT 60k *1 = Burst Mode OPERATION 0 = FIXED FREQUENCY SHDN/SS FB MODE/SYNC RT VC GND R1 340k 9 C2 22µF C4 330pF 10 5 R3 100k Burst Mode OPERATION 80 70 60 50 VIN = 4.2V VIN = 2.5V VIN = 3.3V 40 30 20 R2 200k 10 fOSC = 1MHz C1: TAIYO YUDEN JMK212BJ106MG JMK212BJ106MG C2: TAIYO YUDEN JMK325BJ226MM JMK325BJ226MM L1: SUMIDA CDRH4D28-100 CDRH4D28-100 0 0.1 DN275 DN275 F01 Figure 1. Simple Lithium-Ion to 3.3V Converter at 600mA 01/02/275 90 EFFICIENCY (%) 4 SW1 SW2 LTC3440 LTC3440 6 7 VIN VOUT 3 VIN = 2.5V TO 4.2V , LTC and LT are registered trademarks of Linear Technology Corporation. Burst Mode is a registered trademark of Linear Technology Corporation. 1.0 10 100 OUTPUT CURRENT (mA) 1000 DN275 DN275 F02 Figure 2. Li-Ion to 3.3V Efficiency of over 85% are achieved for more than three decades of load current. At 200µA, the efficiency remains above 70%, primarily due to the low 25µA quiescent current in Burst Mode operation. In many applications the decreased load demand on the converter is known by the application and the converter can be commanded to enter power saving Burst Mode operation by driving the MODE/SYNC pin high. voltage. Figure 4 demonstrates the efficiency of the converter versus input voltage at various load currents. The transient response of the power converter for a 1.5V output voltage change, commanded by the DAC, is shown in Figure 5. 100 98 VOUT = 3.4V 96 IOUT = 100mA 94 EFFICIENCY (%) WCDMA Dynamically Controlled Power Amp Power Supply For the new 3rd generation (3G) cellular phones, the high speed data transmission imposes a stringent power demand on the battery. Maximum overall efficiency and operation over the entire battery voltage range are required to maximize run time. A 2W, dynamically controlled power supply for a WCDMA cell phone power amplifier (PA) is shown in Figure 3. By adjusting the voltage across the PA, the overall efficiency to the antenna is improved, and a linear PA can be utilized. At peak power, the PA requires the highest programmed voltage, typically 3.4V to 4V depending on the PA. At the lowest power level, when only voice is transmitted and the user is close to the basestation, the PA draws less than 100mA and requires a lower voltage, typically between 0.4V to 2V. Since the LTC3440 LTC3440 can regulate an output voltage above, below or equal to the battery voltage, the maximum transmit power can be maintained over the entire voltage range. For applications requiring a program voltage below 2V, a Schottky diode is required from the SW2 to VOUT pins to provide a low impedance power path since the internal synchronous switch looses gate drive at low output 92 IOUT = 250mA 90 88 IOUT = 600mA 86 84 82 80 2.5 3 4 4.5 3.5 INPUT VOLTAGE (V) 5 DN275 DN275 F04 VOUT 1V/DIV Figure 4. Efficiency of the WCDMA Power Amp Power Supply 4.5V 2.6V 0V 4.5V COMMAND 50µs/DIV DN275 DN275 F05 2.6V COMMAND Figure 5. Output Voltage Transient Response of the WCDMA Power Supply VOUT = 3.3V 1.7V (VPROG 1.22) DAC L1 3.3µH D1 C3 33pF 4 SW1 SW2 LTC3440 LTC3440 6 7 VIN VOUT 3 VIN = 2.5V TO 4.2V 8 Li-Ion + C1 * 10µF 2 1 SHDN/SS FB MODE/SYNC VC RT RT 30k GND R1 340k 9 10 R3 15k C4 150pF 5 C5 10pF VOUT 0.4V TO 5V 600mA R5 10k R6 200k R2 200k C2 10µF fOSC = 1MHz *1 = Burst Mode OPERATION C1, C2: TAIYO YUDEN JMK212BJ106MM JMK212BJ106MM D1: ON SEMICONDUCTOR MBRM120T3 MBRM120T3 0 = FIXED FREQUENCY L1: SUMIDA CDRH4D28-3R3 CDRH4D28-3R3 DN275 DN275 F03 Figure 3. WCDMA Power Amp Power Supply with Dynamic Voltage Control Data Sheet Download http://www.linear.com/go/dnLTC3440 Linear Technology Corporation For literature on our Buck-Boost Converters, call 1-800-4-LINEAR 1-800-4-LINEAR. For applications help, call (408) 432-1900, Ext. 2759 dn275f LT/TP 0102 371.5K · PRINTED IN THE USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 q FAX: (408) 434-0507 q www.linear.com © LINEAR TECHNOLOGY CORPORATION 2002