DEMO CIRCUIT 1276B QUICK START GUIDE LTC3558EUD: Linear USB Battery Charger with Buck and Buck-Boost Regulators DESCRIPTION Demonstration Circuit DC1276B is a Linear USB Battery Charger with Buck and Buck-Boost Converters featuring the LTC®3558EUD. The LTC3558EUD is a linear battery charger IC for Li-Ion/polymer battery applications, with a general purpose synchronous stepdown switching regulator and a general purpose buckboost regulator. For USB powered applications, the battery charge current can be limited to 500mA, by setting RPROG to 1.74 kΩ. For non-USB powered applications, the charge current can be set as high as 950mA, by simply changing RPROG. The buck and the buck-boost switching regulators can deliver up to 400mA load current, each. The LTC3558EUD is available in 20-pin (3mm × 3mm) QFN surface mount package. Design files for this circuit board are available, call the LTC factory. , LTC and LT are registered trademarks of Linear Technology Corporation. PowerPath is a trademark of Liner Technology Corporation. PERFORMANCE SUMMARY Specifications are at TA = 25°C SYMBOL VCC VFLOAT IBAT PARAMETER Input voltage range BAT float voltage Battery charge current VOUT1 VOUT2 Buck regulator output voltage Buck-Boost regulator output voltage CONDITIONS Constant Voltage mode Constant current mode, RPROG = 1.74kΩ, HPWR=HI IOUT1 ≤ 400mA IOUT2 ≤ 400mA MIN 4.35 4.15 0.46 1.17 3.27 TYP MAX 5.5 4.23 0.5 UNITS V V A 1.23 3.33 V V QUICK START PROCEDURE Demo Circuit DC1276B is best evaluated using a LiIon or Li-Polymer battery. When using a battery simulator for evaluation, oscillations must be verified with a real battery at the same conditions because it is difficult to match the impedance of a real battery. Capacitor C10 was added to simulate the low impedance of a real battery. It will allow proper operation of the demo circuit with or without a battery and even with a battery simulator consisting of a power supply in parallel with a 3.6 Ohm resistor. Refer to Figure 1 for the proper measurement equipment setup and jumper settings and follow the procedure below. NOTE. When measuring the input or output voltage ripple, care must be taken to avoid a long ground lead on the oscilloscope probe. Measure the input or output voltage ripple by touching the probe tip directly across the VCC or VOUT(x) and GND terminals. See Figure 2 for proper scope probe technique. 1. Set PS1 to 5.0V, and PS2 to 3.6V. 2. Observe AM1, AM4, VM2, VM3, VM4, VM5, and VM6. QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC1276B HIGH EFFICIENCY USB POWER MANAGER WITH BUCK AND BUCK-BOOST REGULATORS LTC3558EUD 3. Set the HPWR jumper (JP1) to “20%”. Observe AM1 and AM4. 4. Set the NTC jumper (JP3) to “EXT”. Observe VM3. The “CHRG” LED (D1) should be blinking. 5. Set the HPWR jumper (JP1) to “100%”, the SUSP jumper (JP2) to “OFF” and the NTC jumper (JP3) to “INT”. 6. Set Ld1 to 400mA. Observe VM4 and AM2. Set Ld1 to 0mA. 7. Set Ld2 to 400mA. Observe VM5 and AM3. Set Ld2 to 0mA. ments a charge termination timeout of 4 hours, and a bad cell charging timeout of 30 minutes. An NTC input is used to determine if the battery temperature is suitable for charging, too hot or too cold. The state of charge, as well as any faults, is signaled with the CHRG pin. Buck Regulator The general purpose 400mA buck regulator is implemented as a current mode, synchronous rectifier regulator, operating at 2.25MHz. Step response is excellent and output ripple is very low. 8. Set EN1 (JP4) and EN2 (JP5) to “OFF”. Observe VM4 and VM5. OPERATING PRINCIPLES The LTC3558 is composed of 3 major functional blocks working together: Battery Charger, Buck Regulator, and Buck-Boost Regulator. The Battery Charger The battery charger is a linear Li-Ion battery charger that operates in constant current mode, until the battery voltage rises to approximately the FLOAT voltage, of 4.2V, and then the charger switches to constant voltage mode. The charge current is programmed by the PROG (R6) resistor, and has been set to 500mA, on DC1276B, with a 1.74kΩ resistor. The HPWR pin is used to select 20% or 100% of the programmed charge current. The charge current delivered is nominally the programmed current, so if the application requires compliance with the USB specification of presenting a 100mA/500mA or less load, the nominal charge current must be set to accommodate the full distribution of actual charge currents. The battery charger implements trickle charging, for initial battery voltages less than 2.9V. It also imple- Buck-Boost Regulator The general purpose 400mA buck-boost regulator is implemented as a voltage mode regulator, operating at 2.25MHz. A type three compensation is recommended for this regulator to achieve the best performance. APPLICATION INFORMATION This demo circuit is designed to demonstrate the full capability of the device. Not all components are required in all applications. The critical circuit components are on the top of the board near the IC. The VCC input capacitor network of C1 and R1 is used to dampen input source inductances that 2 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC1276B HIGH EFFICIENCY USB POWER MANAGER WITH BUCK AND BUCK-BOOST REGULATORS LTC3558EUD commonly occur in laboratory setups with twisted leads and a bench power supply. When using a USB cable or adaptor cable this input damping network will likely not be required. Please note that the incircuit capacitance of the specified 10uF, 0603 ceramic capacitor for C1 is approximately 5uF each at 5V. Capacitor C9 is included to simulate a low impedance battery. It is especially helpful when testing the demo circuit with a battery simulator comprised of a power supply with a 3.6 Ohm power resistor across it. The leads connecting the power supply to the demo circuit should be a twisted pair to minimize lead inductance; although, even twisted pairs can introduce enough inductance into the circuit to turn on overshoot without damping resistor R17. Power dissipation The LTC3558 implements a linear battery charger with no pre-regulator. The battery charge current can be set as high as 0.95A, by choosing the appropriate PROG (R6) resistor. For a typical application of USB charging of a battery, VCC = 5V, BAT = 3V. The θJA of the package is 68°C/W, and the maximum TJ is 125°C. Thus, for TA(max) = 50°C the maximum charge current without thermal regulation can be as high as 550mA. If a higher charge current is desired, the PROG resistor (R6) can be changed. If the resultant power dissipation exceeds the package dissipation rating the LTC3558 will go into thermal regulation, and reduce charge current to an acceptable level. 3 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC1276B HIGH EFFICIENCY USB POWER MANAGER WITH BUCK AND BUCK-BOOST REGULATORS LTC3558EUD VM3 + - + + VM2 PS1 2A - Ld1 0V - 5V - 1 2A + + + 4.35V - 5.5V supply + AM2 VM4 - AM1 - - + - - VM1 VM5 - + + - + 2A + +A VM6 Ld2 0V - 5V AM3 AM4 3.6Ω - PS2 0V - 5V supply + 5A Note: All connections from equipment should be Kelvin connected directly to the board pins which the are connected on this diagram and any input or output leads should be twisted pair. Figure 1. Proper Measurement Equipment Setup for DC1276B GND VIN Figure 2: Measuring Input or Output Ripple 4 GND JP2 SUSP 20% JP1 HPWR E10 E9 0 JP6 MODE OFF JP5 EN2 OFF 1 ON ON BAT 0 INT 0 100K JP4 EN1 R5 R4 EXT OFF 100% R1 1.0 5% C1 10 6.3V 0603 R3 E6 E8 MODE EN2 5 4 3 TP1 DTP2 D+ TP3 ID CHARGER ON GND ID D+ D- 2 1 R2 100K R9 1.0M R8 1.0M R7 1.0M VCC JP3 NTC E5 E7 PROG EN1 E3 E2 E4 NTC SUSP HPWR GND USB VBUS E1 VCC 4.35V - 5.5V J1 ENTC R6 1.74K 3 15 5 18 17 12 16 MODE EN2 EN1 PROG NTC SUSP HPWR 20 VCC 21 GND LTC3558EUD U1 1 VC2 GND FB2 SWCD2 SWAB2 VOUT2 FB1 SW1 PVIN2 PVIN1 BAT CHRG 14 13 10 9 11 4 6 8 7 2 19 C10 1 10V 330pF C3 C2 10pF 15k R10 R16 324K R12 324k C8 22 6.3V 0805 L2 2.2uH 1072AS-2R2M 1098AS-4R7M L1 4.7uH R18 1k 5% 0603 D1 CHRG GREEN R11 105k R13 121k C4 33pF R14 20 5% R15 649K ENTC CHRG BAT GND ENTC E11 GND E12 VOUT2 3.3V 400mA GND VOUT1 1.2V 400mA E13 E14 E15 GND DF3-3P-2DSA 1 2 3 E16 BAT FLOAT=4.2V 0.5A J2 OPT E17 Unless noted: Resistors: Ohms, 0402, 1%, 1/16W Capacitors: uF, 0402, 10%, 50V JP6 settings BUCK BUCK-BOOST BURST BURST PULSE SKIP PWM C5 22 6.3V 0805 C7 10 6.3V 0603 R17 1.0 5% C9 4.7 6.3V 0603 MODE 1 0 TP4 C6 22pF BAT QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC1276B HIGH EFFICIENCY USB POWER MANAGER WITH BUCK AND BUCK-BOOST REGULATORS LTC3558EUD Figure 3: Circuit Schematic 5 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC1276B HIGH EFFICIENCY USB POWER MANAGER WITH BUCK AND BUCK-BOOST REGULATORS LTC3558EUD Figure 4: Bill of Materials 6