DEMO CIRCUIT 1448 LTC3455EUF-1 QUICK START GUIDE LTC3455EUF-1 Dual DC/DC Converter with USB Power Manager and Li-Ion Battery DESCRIPTION Demonstration circuit 1448 is a Dual DC/DC Converter verters and reset and power button status outputs for with USB Power Manager and Li-Ion Battery Charger interface with a microprocessor. featuring the LTC3455EUF-1. Power may be received The LTC3455EUF-1 is available in a 4mm x 4mm 24- from the USB input, a Wall Adapter, or a battery. DC1448 pin exposed-pad QFN package. provides the following functions 700mA CC/CV timer Design files for this circuit board are available. Call terminated charger suitable for Li-ion cells, USB power the LTC factory. manager that ensures compliance with the USB power L, LTC, and Burst Mode are registered trademarks of Linear Technology Corporation. Hot specification, two 1.5MHz synchronous step down con- Swap is a trademark of Linear Technology Corporation. Other product names may be trade- marks of the companies that manufacture the products. PERFORMANCE SUMMARY Specifications are at T = 25C A PARAMETER CONDITIONS MIN TYP MAX UNITS Wall Adapter Input Voltage Range 4.75 5.5 V USB Input Voltage Range 4.20 5.5 V Battery Charger Iout Vin = 5V, VBat = 3.6V 585 690 795 mA Float Voltage Vin = 5V 4.058 4.142 V Trickle Charge Threshold Vin = 5V (Battery voltage rising) 2.85 V Recharge Threshold V - V 150 mV BAT(REGULATED) RECHARGE USB Current Input Current 500mA Mode Vin = 5V USB Active 500mA Mode 440 500 mA Input Current 100mA Mode Vin = 5V USB Active 100mA Mode 60 100 mA Input Current Suspend Mode Vin = 5V USB Suspend 4 20 uA Buck Converters Switcher 1 1.72 1.86 V Switcher 2 3.02 3.27 V Hot Swap Output VBat 3.6V 3.02 3.27 V OPERATING PRINCIPLES Demo Circuit 1448 manages the power supplies that voltage outputs via high efficiency step down converters. would be typical for a USB powered device. Power is in- The intermediate voltage bus is preferentially powered put from either the USB cable or an adapter to an inter- from the Wall Adapter, then from the USB input, and fi- mediate voltage bus. This intermediate voltage is then nally from the battery via an ideal diode. The battery used to charge a Li-ion battery and to generate two low charger is a CC/CV timer terminated type capable of 1 L TC3455EUF-1 charge currents of up to 800mA. The two step down LTC3455-1 provides a reset signal for 200msec after converters are high efficiency synchronous Bucks with power up. The ON pin is designed to interface to a push outputs set at 1.8V and 3.15V. Other output settings are button while the PBSTAT reports the button status to possible by altering the feedback resistor ratios. The chip allow the host microprocessor to shut down. Additionally is normally ON if either USB or Wall Adapter is present. If there is an uncommitted op-amp which is used on the the battery is the only source of power then the circuit demo board as a low battery detector. Another possible must be turned on by pressing the ON button and can be use for the uncommitted op-amp would be as an LDO turned off by depressing the OFF button. The OFF button controller to generate an additional output or to augment will only function when in battery power mode. The the peak current capability of one of the existing outputs. QUICK START PROCEDURE Demonstration circuit 1448 is easy to set up to evaluate voltage to 3.6V. Note that the input current from the the performance of the LTC3455EUF-1. Refer to Figure 1 USB does not exceed the USB spec of 500mA. for proper measurement equipment setup and follow the 4. Increase the loads on the outputs. Note that as the procedure below: output load is increased the charging current is de- NOTE. When measuring the input or output voltage ripple, care must be creased and the USB current remains within the taken to avoid a long ground lead on the oscilloscope probe. Measure the 500mA limit. input or output voltage ripple by touching the probe tip directly across the VIN or VOUT and GND terminals. See Figure 2 for proper scope probe 5. Place the USB Current jumper, JP4, in the 100mA po- technique. sition and note that USB input current falls to maintain 1. With power off, connect input power supplies, meters, compliance with the USB input current specification. battery simulator, and output loads as shown in Figure Also note that as the external load is increased the 1. battery will start to discharge to power the VMAX in- termediate voltage bus, illustrating the ideal diode 2. Set the Jumpers on Demo Circuit 1448 as shown be- function of the LTC3455EUF-1 low: 6. Place the USB Suspend jumper, JP5, in the SUSPEND JP1. MODE jumper to CONTINUOUS MODE position. position and note that the USB current falls to under JP3. HOT SWAP OUTPUT jumper to ON position. 100uA to comply with the suspend mode current. JP4. USB CURRENT jumper to 500mA position. Adapter Charging JP5. USB SUSPEND jumper to USB ACTIVE position. 7. Ramp up the wall adapter voltage. When the wall adapter exceeds 4.7V the LTC3455EUF-1 will cease JP6. 3.15V ON/OFF jumper to ON position. drawing current from the USB and switch over to the USB Charging wall adapter. 3. Set the battery simulator voltage to zero slowly raise 8. Note that the charge current to the battery has in- the USB input voltage. When the supply voltage ex- creased to approximately 690mA. ceeds 4.1V the charger should activate and the charge 9. Increase the battery voltage to 4.1V and note that the LED will illuminate. Continue increasing the USB input charge current falls to 0. This illustrates the constant voltage to 5.0V. The battery will be in trickle charge voltage portion of the charging characteristic. mode. Slowly increase the battery voltage. At voltages above 2.85V the battery charge current will increase to approximately 400mA. Continue increasing the battery 2