QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC937A
USB POWER SOLUTION IN DFN 3X4
2
battery charge current (I
BAT
) will increase to 475mA.
Note that the input current from the USB (I
USB
) does
not exceed the USB spec of 500mA.
3.
Now increase the load on the SYSTEM LOAD OUTPUT
(I
OUT
). Note that as the output load is increased the
charging current is decreased and the USB current
remains within the 500mA limit.
4.
Place the USB current jumper in the 100mA position
and note that USB input current falls to maintain
compliance with the USB input current spec. Also
note that as the external load is increased the battery
will start to discharge into the SYSTEM LOAD
OUTPUT, illustrating the ideal diode function of the
LTC4085
5.
Place the USB ON/OFF jumper (JP1) in the OFF posi-
tion and note that the USB current falls to under
300uA to comply with the USB suspend mode cur-
rent.
Adapter Charging
6.
Ramp up the wall adapter voltage. When the wall
adapter exceeds 4.3 volts the LTC4085 will cease
drawing current from the USB and switch over to the
wall adapter. Both the AC-present LED (D1, red) and
charge LED (D2, green) are on.
7.
Note that the charge current to the battery has in-
creased to 700mA.
8.
Increase the battery voltage to 4.2V and note that the
charge current falls to 0. This illustrates the constant
voltage portion of the charging characteristic. In the
mean time, the charge LED (D2) turns off.
Battery Powered Operation
9.
Set Both USB input voltage and the adapter input
voltage to zero. The battery will now power the load
on the System Load Output, illustrating the ideal di-
ode function of the LTC4085. Note that the battery is
now being discharged.
Other
Frequency at charge timer cap C3 changes with charging
current, indicating the adaptive feature to ensure the full
charge of battery.
10.
Pins are provided to all control functions in order to
simplify wiring of the demo circuit into a system
board.
11.
NTC function; provision has been made for connec-
tion of an external 10k NTC, for temperature qualified
charging. To use this feature set the NTC jumper in
the external position and connect the external NTC to
the NTC terminal and ground.
