QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 839
DUAL IDEAL DIODE-TRIPLE POWER PATH CONTROLLER
1
LTC4413
DESCRIPTION
Demonstration circuit 839 is a triple input ideal diode
based PowerPath circuit featuring the LTC4413 dual
Ideal diode controller with dual Integrated MOSFETs.
The circuit allows one of 3 sources to become the
primary power source. Under certain circumstance,
current sharing is possible among all power sources
at any given time. However, only the BAT and USB
inputs can share current equally given identical
sources. Furthermore, only the BAT and USB power
inputs are protected from reverse current flow. Wall
input FET Q1 is not driven as an Ideal Diode.
The WALL input (Q1) will automatically come on
when the voltage is high enough to pick up the load
on Vout being supplied by the BAT input. The turn-on
trip voltage will be Q1’s internal diode drop above
Vout. The LTC4413 will sense the drop in current the
BAT input and turns on Q1 through it status output.
Once Q1 is turned on, Q1’s internal diode drop is
eliminated creating a snap-on hysteresis effect.
Likewise the snap action works in reverse once the
WALL input voltage drops below the BAT input volt-
age allowing the BAT input to supply current to the
load. The USB input has no influence over Q1’s state
unless the BAT input is reversed or disabled. See Ta-
ble 2 for Truth Table Information.
The LTC4413 is offered in a MS08 exposed pad 8 pin
package. Careful PCB layout in terms of heat sinking
is critical to obtaining maximum circuit current. Q1
has no short circuit or thermal overload protection
and care must be taken to not destroy the MOSFET.
The maximum continuous current in free air room
temp is about 2.4A. 2.6A is permissible with some air
cooling or improved thermal management. Current
levels above 280mA, the output voltage drop will be-
come a function of the LTC4413 Rds-on value.
The LTC4413 has weak internal pull-downs that allow
BAT and USB inputs to be on by default with no
connections to the ENBA and ENBB control inputs.
Test points are provided to monitor or control WALL,
BAT, USB, VOUT, ENBA and ENBB. Multiple Ground
Test-points are also provided.
When using ceramic capacitors, care must be taken
to not cause voltage spikes. The 1Ohm resistors ad-
dress this issue. See LT Application Note 88 for more
information.
Design files for this circuit board are available. Call
the LTC factory.
LTC is a trademark of Linear Technology Corporation
