DEMO CIRCUIT 1377A QUICK START GUIDE LTC4088-2 LTC4088-2 High Efficiency Battery Charger/USB Power Manager with Regulated Output Voltage DESCRIPTION Demonstration circuit 1377A is a High Efficiency Battery An ideal diode ensures that system power is available Charger/USB Power Manager with Regulated Output from the battery when the input current limit is reached Voltage featuring the LTC4088-2. The LTC4088-2 in- or if the USB or wall supply is removed. The external P- cludes a synchronous switching input regulator, a full- channel MOSFET supplements the internal ideal diode featured battery charger and an ideal diode. Designed by reducing R and increasing efficiency. ON specifically for USB applications, the LTC4088-2s A CHRG LED indicates four possible states of the bat- switching regulator automatically limits the input current tery charger. Charging is indicated when the LED is to a maximum of 100mA or 500mA for USB applications, steady-ON. Not charging is indicated by a steady-OFF. or 1A for wall-powered applications via logic control. an NTC fault is indicated by a slow blinking rate The switching input stage provides power to VOUT (1.5Hz) and a bad battery is indicated by a fast blink- where power sharing between the application circuit and ing rate (6.1Hz). the battery charger is managed. Charge current is auto- The LTC4088-2 is available in a low profile 14-Lead 4mm matically reduced to maintain a regulated 3.6V VOUT 3mm 0.75mm DFN surface mount package. during low battery conditions. As the battery is charged, VOUT tracks BAT for high efficiency charging. This fea- Design files for this circuit board are available. Call ture allows the LTC4088-2 to provide more power to the the LTC factory. application and eases thermal issues in constrained ap- L, LTC, LT, and PowerPath are registered trademarks of Linear Technology Corporation. plications. Other product names may be trademarks of the companies that manufacture the products. PERFORMANCE SUMMARY Specifications are at T = 25C A SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS V Input Supply Range 4.35 5.5 V BUS V Output Voltage Range V = 5V, 1x, 5x, 10x Modes, 0V < BAT 4.2V 3.5 BAT+0.3 4.7 V OUT BUS V = 5V, USB Suspend Modes, I = 250A 4.5 4.6 4.7 V BUS OUT V BAT Regulated Output Voltage 4.179 4.2 4.221 V FLOAT I Constant-Current Mode Charge Current V = 5V, R = 2K, BAT = 3.8V 490 515 540 mA CHRG BUS PROG I Battery Charge Current at Programmed End of V = 5V, R = 2K 42.5 50 57.5 mV C/X BUS C/X Charge Indication OPERATING PRINCIPLES This demo circuit is designed to demonstrate the full ca- the demo board near the IC and listed in the Required pability of the LTC4088-2 High Efficiency Battery Circuit Components section of the Bill-of-Materials. Charger. Not all components are required in all applica- The input RC network of C6 and R13 is used to dampen tions. The critical circuit components are on the top of source lead inductances that commonly are present in 1 LTC4088-2 laboratory setups with twisted leads and a bench power The RC network of C4 and R8, R9, and R12 is included supply. When using a USB cable or adaptor cable this to simulate a low impedance battery. It is especially help- input damping network will likely not be required. Please ful when testing the demo circuit with a battery simulator note that the in-circuit capacitance of the 10uF, 0805 ce- comprised of a standard power supply with a 3.6 Ohm ramic capacitor specified for C2 and C6 is approximately power resistor across it. The leads connecting the power 5uF each at a VBUS greater than 4.25 Volts. supply to the demo circuit should be a twisted pair to minimize lead inductance although, even twisted pairs The LTC4088-2 requires a minimum of 10uF on the can introduce enough inductance into the circuit to cause VOUT pin in 10X mode for voltage loop stability. As an instability in the battery charger section without the pres- alternative to using two smaller X5R capacitors, one lar- ence of C4. If desired, it is possible to use a ceramic ca- ger X5R ceramic capacitor would be acceptable, pro- pacitor in series with a low valued resistor to stabilize the vided that the actual in-circuit capacitance with 4.6 Volts battery charger when no battery is present. Please refer applied is greater than 10uF. to the datasheet for the suggested capacitor and resis- tance range. QUICK START PROCEDURE Demonstration circuit 1377A is easy to set up to evaluate 3. Use Table 1 to set JP2, JP3, and JP4 (D0, D1, and the performance of the LTC4088-2. Refer to the Per- D2 respectively) to select the desired input current formance Summary for a listing of the inputs and out- limit and charger status. puts of the 1377A Demo Circuit. Demo Circuit 1377A is TABLE 1. Controlled Input Current Limit best evaluated using a Li-Ion/Polymer battery. When us- ing a battery simulator for evaluation, oscillations must D0 D1 D2 CHARGER I BUS(LIM) be verified with a real battery at the same conditions 0 0 0 ON 100mA(1x) because it is difficult to match the impedance of a real 0 0 1 OFF 100mA(1x) battery. Refer to Figure 1 for proper measurement equipment setup and follow the procedure below: 0 1 0 ON 500mA(5x) NOTE. When measuring the input or output voltage ripple, care must be 0 1 1 OFF 500mA(5x) taken to avoid a long ground lead on the oscilloscope probe. Measure the 1 0 0 ON 1A(10x) input or output voltage ripple by touching the probe tip directly across the VBUS or VOUT and GND terminals. See Fig ure 2 for proper scope probe 1 0 1 OFF 1A(10x) technique. 1 1 0 OFF 500uA(Susp Low) 1. If using an external supply, connect a 0 to 6V, 1.5A 2.5mA(Susp high) 1 1 1 OFF supply with voltage adjusted to 0V between the VBUS and GND terminals. Connect a Voltmeter 4. Connect a 0 to 2A adjustable load in series with an across the VBUS and GND terminals. If using the ammeter between the VOUT terminal and the GND USB input option, have the cable ready to plug in terminal. Connect a Voltmeter between the VOUT when all loads and jumpers are set. Do not use the and GND terminals. USB input and an external supply at the same time. 5. Connect a partially charged (~3.6V) Lithium ion 2. Set JP1, NTC jumper, to INT to use the demo board battery with the positive lead to the BAT terminal resistor. To use an external 100kOhm NTC resistor, and the negative lead to a GND terminal. Connect connect the NTC resistor between J2-3 and the the positive lead of a Voltmeter to the BAT terminal GND terminal. Then set the NTC jumper to EXT. and the negative lead to the GND terminal. Connect 2