QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1138A-A/B USB POWER MANAGER WITH Li-ION CHARGER AND TRIPLE BUCK REGULATORS LTC3557/LTC3557-1 + LT3505 DESCRIPTION The DC1138A-A/B contains the vides a high input voltage, high efficiency battery LTC3557/LTC3557-1 Power Management Inte- charger and PowerPath function. An always-on grated Circuit (PMIC) plus the LT3505EDD high LDO provides a regulated 3.3V from VOUT. This voltage buck controller. The LTC3557/LTC3557-1 LDO will be on at all times and can be used to is a highly integrated power management IC that supply up to 25mA. includes a PowerPath controller, battery charger, The LTC3557/LTC3557-1 includes three 2.25MHz an ideal diode, an always-on LDO, three synchro- constant frequency current mode step-down nous step-down switching regulators as well as a switching regulators providing 400mA, 400mA and buck regulator VC controller. Designed specifically 600mA. All step-down switching regulators can be for USB applications, the PowerPath controller programmed for a minimum output voltage of 0.8V incorporates a precision input current limit which and can be used to power a microcontroller core, communicates with the battery charger to ensure I/O, memory or other logic circuitry. All step-down that the input current does not violate the USB switching regulators support 100% duty cycle op- specification. The ideal diode from BAT to VOUT eration and are capable of operating in Burst guarantees that ample power is always available Mode operation for highest efficiencies at light to VOUT even if there is insufficient or absent loads (Burst Mode operation is pin selectable). No power at VBUS. external compensation components are required The LTC3557/LTC3557-1 also has the ability to for the switching regulators. receive power from a wall adapter or other non- The LTC3557/LTC3557-1 is available in a 28- current-limited power source. Such a power sup- pin low profile (4mm x 4mm x 0.75mm) QFN ply can be connected to the VOUT pin of the package. LTC3557/LTC3557-1 through an external device Design files for this circuit board are avail- such as a power Schottky diode or MOSFET, Q1, able by calling the LTC factory. as shown in the demo board circuit schematic, L, LTC, LT and Burst Mode are registered trademarks of Linear Technol- Figure 4. The LTC3557/LTC3557-1 has the ogy Corporation. PowerPath is a trademark of LinearTechnology Corpora- tion. Other product names may be trademarks of the companies that manu- unique ability to use the output, which is powered facture the products. by an external supply, to charge the battery while providing power to the load. A comparator on the WALL pin is configured to detect the presence of the wall adapter and shut off the power connection between VOUT and the USB input. This prevents reverse conduction from VOUT to VBUS when a wall adapter is present. The LTC3557/LTC3557-1 provides a VC output pin which can be used to drive the VC pin of an external high voltage buck switching regulator such as the LT3480, LT3481, or LT3505 to provide power to the VOUT pin. The VC control circuitry adjusts the regulation point of the switching regu- lator such that VOUT equals the greater of BAT Figure 1. LTC3557/LTC3557-1 Simplified Typical plus 300mV or 3.6 Volts. This control method pro- Application 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1138A-A/B USB POWER MANAGER WITH Li-ION CHARGER AND TRIPLE BUCK REGULATORS LTC3557/LTC3557-1 + LT3505 Table 1. Typical Specifications (25C) RANGE PARAMETER VBUS 4.35V to 5.5V 5V ADAPTER 4.5V to 5.5V HVIN 8V to 36V VOUT 2.9V 5.5V, 1.2A VOUT1 3.3V, 600mA VOUT2 1.2V, 400mA VOUT3 1.8V, 400mA LDO3V3 3.3V, 25mA Battery Float Voltage in Constant Voltage Mode LTC3557EUF = 4.2V (DC1138A-A), LTC3557EUF-1 = 4.1V (DC1138A-B) Battery Charge Current in Constant Current Mode 500mA (R = 2K Ohms) PROG QUICK START PROCEDURE Demo Circuit 1138 is best evaluated using a 2. Set the NTC jumper to INT to use the lithium ion battery. The test set-up in Figure 2 demo board resistors. To use an external shows a battery simulator, consisting of PS4 NTC resistor, connect an NTC resistor be- and a 3.6 Ohm power resistor. Since the tween J2-3 (ENTC) and GND. Then set demo circuit is designed to possibly be used the NTC jumper to EXT. with a battery simulator, it includes a capacitor 3. Use Table 2 to set ILIM1 and ILIM0 to se- between the BAT and GND terminals with lect the desired input current limit. some series resistance. Please see the Ap- Table 2. Maximum Current Limit Settings plications Section below for a detailed discus- sion of selecting the proper bypass capacitor ILIM1 ILIM0 MAXIMUM INPUT CURRENT LIMIT and series resistance for the BAT terminal. 0 0 100mA Refer to Figure 2 for the proper measurement 01 1A and equipment setup and follow the proce- 1 0 SUSPEND dure below. 1 1 500mA 1. Set all Power Supplies to zero volts and all loads to zero amps and then connect the 4. Set EN1, EN2 and EN3 to ON. test equipment as shown in Figure 2. If 5. Set PS4 to 3.6 Volts. Alternatively, PS4 using the USB input option, have cable and the Power resistor could be replaced ready to plug in for when all loads and with a lithium ion battery conditioned to 3.6 jumpers are set. Do not use the USB in- Volts. Observe VOUT, VOUT1, VOUT2, put and an external supply at the same VOUT3 and LDO3V3 outputs. time. 2