DC839A Analog Devices

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 839 DUAL IDEAL DIODE-TRIPLE POWER PATH CONTROLLER LTC4413 DESCRIPTION Demonstration circuit 839 is a triple input ideal diode The LTC4413 is offered in a MS08 exposed pad 8 pin based PowerPath circuit featuring the LTC4413 dual package. Careful PCB layout in terms of heat sinking Ideal diode controller with dual Integrated MOSFETs. is critical to obtaining maximum circuit current. Q1 has no short circuit or thermal overload protection The circuit allows one of 3 sources to become the and care must be taken to not destroy the MOSFET. primary power source. Under certain circumstance, current sharing is possible among all power sources The maximum continuous current in free air room at any given time. However, only the BAT and USB temp is about 2.4A. 2.6A is permissible with some air inputs can share current equally given identical cooling or improved thermal management. Current sources. Furthermore, only the BAT and USB power levels above 280mA, the output voltage drop will be- inputs are protected from reverse current flow. Wall come a function of the LTC4413 Rds-on value. input FET Q1 is not driven as an Ideal Diode. The LTC4413 has weak internal pull-downs that allow The WALL input (Q1) will automatically come on BAT and USB inputs to be on by default with no when the voltage is high enough to pick up the load connections to the ENBA and ENBB control inputs. on Vout being supplied by the BAT input. The turn-on Test points are provided to monitor or control WALL, trip voltage will be Q1s internal diode drop above BAT, USB, VOUT, ENBA and ENBB. Multiple Ground Vout. The LTC4413 will sense the drop in current the Test-points are also provided. BAT input and turns on Q1 through it status output. When using ceramic capacitors, care must be taken Once Q1 is turned on, Q1s internal diode drop is to not cause voltage spikes. The 1Ohm resistors ad- eliminated creating a snap-on hysteresis effect. dress this issue. See LT Application Note 88 for more Likewise the snap action works in reverse once the information. WALL input voltage drops below the BAT input volt- age allowing the BAT input to supply current to the Design files for this circuit board are available. Call load. The USB input has no influence over Q1s state the LTC factory. unless the BAT input is reversed or disabled. See Ta- LTC is a trademark of Linear Technology Corporation ble 2 for Truth Table Information. 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 839 DUAL IDEAL DIODE-TRIPLE POWER PATH CONTROLLER Table 1. Performance Summary PARAMETER CONDITION/NOTES MAX VALUE Maximum Input Voltage 5.5V Minimum Input Voltage 2.5V Datasheet Max Current BAT Thermally Limited 2.6A & USB 839 Max Current BAT & USB Room temp, No fan, 5V on BAT or USB input 2.4A Typical Voltage Drop 3.6V on BAT or USB input. 100mOhm Rds-on. 50mV 0.5A Typical Transition Current 3.6V, From Vfwd = Regulated 28mV to = (Rds-on x 280mA Iload) Thermal Overload Current Thermal overload caused by Short Circuit on output. 1.8A min. Limit Typical DCIN MOSFET Rds- Fairchild FDC606P 2.5Vgs / 4.5Vgs 35mOhm / 26mOhm on Maximum Current on WALL Thermally Limited. 4A 2.5V input Table 2. Q1 & LED State table BAT FOWARED CURRENT USB FORWARD CURRENT WALL (Q1) / LED STATE OFF OFF ON OFF ON ON ON OFF OFF ON ON OFF Disabled OFF ON Disabled ON OFF OFF Disabled ON ON Disabled OFF Disabled Disabled ON 2