DC1085 DC1085 QUICK START GUIDE QUICK START GUIDE LTC3559 Linear USB Battery Charger with Dual Buck Regulators DESCRIPTION Demonstration circuit 1085 is a Linear USB Battery Each monolithic synchronous buck regulator provides up Charger with Dual Buck Regulators featuring the to 400mA of output current while operating at efficien- LTC3559. The LTC3559 is a USB battery charger with cies greater than 90% over the entire Li-Ion/Polymer dual high efficiency buck regulators. The part is ideally range. A MODE pin provides the flexibility to place both suited to power single cell Li-Ion/Polymer based hand- buck regulators in a power saving burst mode operation held applications needing multiple supply rails. or a low noise pulse skip mode. Battery charge current is programmed via the PROG pin The LTC3559 is offered in a low profile thermally en- and the HPWR pin, with capability up to 950mA at the hanced 16-lead (3mm 3mm) QFN package. BAT pin. The battery charger has an NTC input for tem- Design files for this circuit board are available. Call perature qualified charging. The CHRG pin allows battery the LTC factory. status to be monitored continuously during the charging L, LTC, LTM, LT, Burst Mode, are registered trademarks of Linear Technology Corporation. process. An internal timer controls charger termination. All other trademarks are the property of their respective owners. TABLE 1. TYPICAL SPECIFICATIONS (25C) 4.35V to 5.5V Input Voltage Range: V CC VOUT1 25C 2.5V, 2.5%, 400mA (Max) VOUT2 25C 1.2V, 2.5%, 400mA (Max) Output Float Voltage V (constant voltage mode) 4.2V BAT Output Charge Current I (constant current mode) 500mA maximum (R = 1.74K and Jumper HPWR = 100%) BAT PROG OPERATING PRINCIPLES The LTC3559 is a linear battery charger with dual via a single PROG resistor. The actual BAT pin cur- monolithic synchronous buck regulators. The buck rent is set by the status of the HPWR pin. regulators are internally compensated and need no For proper operation, the BAT and PVIN pins must external compensation components. be tied together. If a buck regulator is also enabled The battery charger employs a constant-current during the battery charging operation, the net cur- constant-voltage charging algorithm and is capable rent charging the battery may be lower than the ac- of charging a single Li-Ion battery at charging cur- tual programmed value. rents up to 950mA. The user can program the maximum charging current available at the BAT pin 1 DC1085 QUICK START GUIDE QUICK START PROCEDURE Using short twisted pair leads for any power connec- 8. Remove the NTC jumper and observe the CHRG LED slow blink rate indicating a temperature fault. Replace tions and with all loads and power supplies off, refer the NTC Jumper. to Figure 1 for the proper measurement and equip- ment setup. The Battery should not be connected to 9. Monitor the battery voltage and current (via VPROG) the circuit until told to do so in the procedure below. as it charges to its float voltage (4.2 Volts). The CHRG LED will be ON, indicating that the battery is charging th NOTE. When measuring the input or output voltage ripple, care must be until the charge current drops to 1/10 of its pro- taken to avoid a long ground lead on the oscilloscope probe. Measure the grammed value. The charger will continue to supply input or output voltage ripple by touching the probe tip directly across the current into the battery until the 4 hour safety timer VCC or VOUT and GND terminals. See Figure 2 for proper scope probe technique. has timed out. 1. Place jumpers in the following positions: JP1 HPWR = 100% APPLICATION INFORMATION JP2 EN1 = ON This demo circuit is designed to demonstrate the full JP3 EN2 = ON capability of the LTC3559 Linear USB Battery Charger JP4 MODE = PULSE SKIP with Dual Buck Regulators. Not all components are JP5 SUSP = ON required in all applications. The critical circuit com- ponents are on the top of the board near the IC and JP6 NTC = INT listed in the Required Circuit Components section of the Bill of Materials, see Figure 4. 2. Connect a battery charged to 3.6 Volts to the demo board as shown in Figure 1. The input capacitor network of C7 and R15 is used to dampen source lead inductances that commonly oc- 3. Verify that VOUT1 and VOUT2 are operational with cur in laboratory setups with twisted leads and a proper output voltages. bench power supply. When using a USB cable this 4. Once the proper output voltages are established, ad- input damping network will likely not be required. just the loads within the operating range and observe Please note that the in-circuit capacitance of the the output voltage regulation, ripple voltage, and effi- specified 10uF, 0805 ceramic capacitor for C7 is less ciency. than 5uF with VCC greater than 4.25 Volts. 5. Set PS1 to 5.0 Volts. Turn on PS1 and verify that the input current measured by ammeter, AM1, does not Capacitor C8 and resistor R12 are included for battery exceed the USB limit of 500mA. charger stability in float mode when the battery is NOTE. Make sure that the Vcc node does not exceed 6V. temporarily not present. Increasing input capacitor 6. Verify that VOUT1 and VOUT2 are operational with C1 to 10uF will allow the part to operate without a bat- proper output voltages. tery, provided that the input current limit is not ex- ceeded. A 100uF, 6.3V, OSCON capacitor in a B6 case 7. Monitor the PROG voltage for a representation of the may be required on the BAT pin when testing is per- battery charge current. I = 800V / R BAT PROG formed with a battery simulator comprised of a power supply with a 3.6 Ohm power resistor across it. Refer 2