advertisement Universal Li-Ion Battery Charger Operates from USB and 6V to 36V Input in Just 2cm2 – Design Note 395 Liu Yang 3mm × 6mm DFN package. The LTC4089’s buck regulator output voltage tracks the battery voltage to within 300mV. This Bat-TrackTM feature minimizes overall power dissipation. The LTC4089-5 has a fixed 5V at OUT when power is applied at HVIN. When power is supplied from the USB port, the power manager maximizes the available power to the system load; up to the full USB available power of 2.5W. It automatically adjusts the Li-Ion battery charge current with respect to the system load current to maintain the total input current compliance within the USB limits. The total solution size is less than 2cm2 with all components on one side of the PCB. Introduction There are a number of advantages to offering USB and high input voltage power and battery-charging capability in handheld devices such as GPS navigators, PDAs, digital still cameras, photoviewers and MP3 players. For instance, charging and operation from USB offers the obvious convenience of not requiring a travel adapter. High voltage sources, such as Firewire and 12V to 24V adapters are even better, since they provide faster charging than USB and allow charging in more places, such as in the car. Nevertheless, there is an important design consideration with high voltage power sources: the voltage difference between the high voltage source and the battery in the handheld is very large. Since a linear charger cannot handle the power dissipation, a switching charger is required. Adaptive High Voltage Buck Minimizes Total Power Loss The LTC4089’s buck converter output voltage VOUT tracks the battery voltage VBAT. It is always 0.3V higher than VBAT, so that the battery can be charged quickly while The LTC® 4089 and LTC4089-5 (see Figure 1) conveniently integrate a high voltage and wide input range (6V to 36V with 40V absolute maximum) monolithic 1.2A buck switching regulator and a USB power manager/charger into a compact thermally enhanced , LT, LTC and LTM are registered trademarks of Linear Technology Corporation. Bat-Track is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. D2 C2 0.1µF 20 BOOST SW L1 10µH 19 C3 22µF 6.3V D1 HVIN 6V TO 36V 21 C1 1µF 50V HVIN HVOUT HVEN HVOUT 3 18 22 7 HVPR USB 4.35V TO 5.5V 12 C5 4.7µF 6.3V 15 C4 0.15µF 16 17 R3 2.1k 14 R4 71.5k 9 OUT IN HPWR GATE SUSP BAT CHRG TIMER VNTC C10 10pF GND 4 2 NTC GND 1 (TO SYSTEM LOAD) 13 10 C6 4.7µF 6.3V Q2 11 8 OUT Li-ION+ (OPTIONAL) 6 CLPROG PROG VC Q1 R6 10k U1 LTC4089EDJC 5 R5 10k 1% RNTC 10k DN395 F01 Figure 1. The LTC4089 Schematic Illustrates Multiple Input Voltage Capability 08/06/395 minimizing overall power dissipation. Figure 2 shows the overall efficiency at various input voltages, where the total power dissipation is less than 1.1W. Furthermore, if the battery is excessively discharged and VBAT falls too low, the minimum VOUT is 3.6V to ensure continuous system operation. USB Power Manager Maximizes Power Available to the System In a traditional dual input device, the input charges the battery and the system’s power is directly taken from the battery. This creates a number of problems. One of these is that the system’s available power is reduced by the low-battery voltage when there is USB power present. For example, when VBAT = 3.3V, the available power to the system is only 1.65W while the USB itself supplies 2.5W. The balance is dissipated as heat. The LTC4089 successfully solves this problem by providing an intermediate voltage VOUT to power the system load. 1.3 1.2 80 1.1 75 1.0 70 0.9 65 0.8 CHARGER EFFICIENCY 0.7 BUCK EFFICIENCY TOTAL EFFICIENCY 0.6 TOTAL PLOSS 0.5 10 15 20 25 30 35 40 HIGH VOLTAGE INPUT (V) 0 5 The LTC4089 integrates a high voltage wide input monolithic switching regulator, USB power manager and Li-Ion battery charger into a 3mm × 6mm DFN package and improves the functionality of USB-based and multiple power input portable devices. 1.4 85 55 Summary TOTAL POWER LOSS (W) EFFICIENCY (%) VBAT = 3.5V 95 IBAT = 700mA IOUT = 0 90 50 Small Footprint With all the necessary components on the same side of the PCB, the total solution size is less than 2cm2 (11.3mm × 17.5mm) as shown in Figure 3. 1.5 100 60 This VOUT is independent of the battery voltage and equal to the USB voltage, thus the full USB power is available to the system load. Table 1 shows the advantages of the LTC4089 power manager over the traditional dual input configuration. DN395 F02 Figure 2. The LTC4089 High Voltage Charger Efficiency and Total Power Loss DN395 F03 Figure 3. The LTC4089 Demo Circuit with Layout in Bottom Right Corner Table 1. Comparison of Traditional Dual Input Charger and Linear Technology’s LTC4089 Power Manager/Charger for USB Charging SCENARIO Battery voltage is below trickle charging voltage Battery is not present VBAT = 3.3V at USB input System consuming close to the input power limit TRADITIONAL DUAL INPUT CHARGER LTC4089 POWER MANAGER/CHARGER Available current to system is only trickle charge current (50mA to 100mA), which may not be sufficient to start the system Most chargers consider this as a fault. The system cannot start Available power to system is only 1.65W. The system power cannot be greater than this Cannot distinguish the available charging current. Charger timer runs out before the battery is fully charged Full adapter/USB power is available to system, although battery is in trickle charge Full adapter/USB power is available to system Full 2.5W USB power is available to the system Charger time proportionally increases with less available charge current. The battery is always fully charged Data Sheet Download http://www.linear.com For applications help, call (408) 432-1900, Ext. 2364 Linear Technology Corporation dn395f LT 0806 305K • PRINTED IN THE USA FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2006 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ●