advertisement Shrink Battery-Powered Products with a Combination Battery Charger and DC/DC Converter – Design Note 1002 Tom Hack Introduction Until now, power management in portable devices or systems with battery backup have required a mix of major components to fulfill the basic functions of battery charging and generation of system supply voltages. A typical solution requires at least one charger IC for charging the battery, another IC to supply a regulated system bus voltage from a constantly changing battery voltage, PowerPath™ control and a low dropout regulator (Figure 1). Space is at a premium in these ever shrinking portable products, creating an imperative to shrink the power circuitry as well. The LTC®1980 solves the space problem by combining these functional blocks into a single IC. The result is a substantial reduction in the complexity of portable power systems (Figure 2). How the LTC1980 Reduces Size and Cost The LTC1980 manages both battery charging and generaton of the regulated system bus voltage via a unique bidirectional pulse-width modulator design (Figure 3). When the wall adapter is present, power passes directly to the system load DC/DC converters and to a pulse widthmodulated battery charger formed by M1, M2, T1 and the LTC1980. With the wall adapter present, power flows into CHARGE TERMINATION the battery. With the wall adapter removed, power flows in the opposite direction, out of the battery, and is regulated through the DC/DC converter formed by the same power components. In this way, a single bidirectional supply replaces two traditional pulse width modulated supplies producing a substantial parts savings. No additional power routing/management is needed, further reducing the parts count and power losses that would be incurred by the additional circuitry. 4.1V/1A Li-Ion Battery Charger and 3.3V DC/DC Converter Figure 4 shows a 4.1V/1A Li-Ion battery charger and 3.3V DC/DC converter. The LTC1980 includes a complete PWM regulator controller, PowerPath management functions and charge termination (including pre-trimmed 4.1V, 4.2V, 8.2V and 8.4V float voltages, under- and overvoltage protection, trickle-charge cell conditioning and charge termination timing). Other battery chemistries may be externally programmed. This design is compatible with both regulated and unregulated wall adapters (minimum output voltage 4.1V). For higher voltage wall adapters, adjust R15 to increase the wall-adapter detection threshold. D1 is optional and provides protection against accidental wall-adapter connector shorts—a problem in some products that use charging cradles with exposed connections. , LTC and LT are registered trademarks of Linear Technology Corporation. PowerPath is a trademark of Linear Technology Corporation. FROM WALL ADAPTER BATTERY CHARGER PowerPath CONTROL PWM REGULATOR LOW DROPOUT REGULATOR TO SYSTEM LOAD DC/DC CONVERTERS DN1002 F01 FROM WALL ADAPTER LTC1980-BASED POWER DESIGN DN1002 F02 Figure 1. Traditional Portable Power System 12/03/1002 TO SYSTEM LOAD DC/DC CONVERTERS Figure 2. An LTC1980-Based Portable Power System • T1 Li-Ion BATTERY WALL ADAPTER T1 Li-Ion BATTERY • M1 M1 SYSTEM LOAD DC/DC CONVERTERS RS ISENSE • M2 • M2 SYSTEM LOAD DC/DC CONVERTERS RS ISENSE LTC1980 LTC1980 DN1002 F03a DN1002 F03a (3b) DC/DC Converter Mode (Wall Adapter Removed) (3a) Battery Charger Mode Figure 3. LTC1980 Bidirectional Power Conversion VBAT + 4.1V Li-Ion BATTERY C1 68µF D1* 5819 BH511-1014 + VREG + • 5.1Ω 1nF M1 1/2 FDC6401N WALL ADAPTER C4 68µF 5.1Ω OPTIONAL PASS TRANSISTOR FOR LDO FDC636P 1nF M2 1/2 FDC6401N • 50mΩ RSENSE 14 BGTDR 18 VBAT 23 OVP 3 REGFB 22 CAOUT PROG 1 R9 10k 12 R11 1M 21 GND ISENSE 11 7 6 5 PROGT C11 1nF VC TIMER 4 17 C7 0.27µF 15 REG 16 MODE 9 BATT1 10 BATT2 C12 82pF R13 806k SS 24 C8 0.1µF WA VBIAS1 C9 1µF 200pF ACIN VLDO 3.1V SYSTEM LOAD DC/DC CONVERTERS C6 470µF R5 154k R6 100k 8 RGTDR VREG LDODRV LDOFB LTC1980 2 R10 110k M3 20 PGND DCOUT 3.3V VOUT R15 221k 1% R7 100k 1% R8 169k VBIAS2 13 C10 0.33µF 19 R14 100k R12 100k *OPTIONAL DIODE FOR SHORTED WALL ADAPTER TERMINAL PROTECTION. DN1002 F04 Figure 4. 4.1V/4.2V Selectable 1A Li-Ion Battery Charger and 3.3V DC/DC Converter Conclusion The LTC1980 helps reduce size, complexity and lowers the cost of portable products by integrating a DC/DC converter and battery charger circuitry into a single IC. It also offers high efficiency, increasing battery run time and lowering power dissipation during battery charging. 90 85 EFFICIENCY (%) High Efficiency Makes for Cool Running Products and Extends Operating Time Between Charges Peak DC/DC converter efficiency, excluding the optional, low dropout regulator is over 88% (see Figure 5). In addition, the LTC1980 uses pulse-width modulated charging. When compared to linear chargers, there is less power dissipation keeping operating temperatures lower. 80 75 70 VBAT = 3.6V TA = 25°C FIGURE 4 65 60 10 100 LOAD CURRENT (mA) 1000 DN1002 F05 Figure 5. Regulator Efficiency vs Load Current Data Sheet Download http://www.linear.com Linear Technology Corporation For applications help, call (408) 432-1900, Ext. 2593 dn1002 LT 1203 • PRINTED IN THE USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2003