QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC867
DUAL INPUT USB / AC ADAPTER STANDALONE LI-ION CHARGER
1
LTC4075XEDD
DESCRIPTION
Demonstration circuit DC867 features the
LTC4075X standalone linear charger that is capa-
ble of charging a single-cell Li-Ion battery from
both AC adapter and USB inputs. DC867 is de-
signed to demonstrate the LTC4075X capability to
automatically select the appropriate power source
for charging. DC867 is set up so that when the
USB source is used as the input, the charge cur-
rent is set to 500mA and when the AC adapter is
available, regardless of the USB input connection,
the charge current increases to 800mA.
The enable operation of the LTC4075X changes
with different input sources. When the LTC4075X
is charging from the AC adapter source, a “logic
low” enables the charger and when the USB input
is used for charging, “logic high” is needed to acti-
vate the LTC4075X. DC867 is design to start
charging with AC adapter as default mode. For
USB input charging, the JP1 jumper has to be set
to the
USB on
position or the
USB ENABLE
pin
(turret) has to be pulled above 1V. The jumper
setting can be
USB on
for AC adapter charging
mode but the
USB ENABLE
terminal (turret) has
to be floating or pulled low to enable AC adapter
mode charging.
There are two LED indicators (the third LED is for
optional “USB power” indication) for battery
charge status and input power status. The
“CHRG” LED will be turned on when LTC4075X is
charging and it will be turned off when charging is
terminated or the LTC4075X is disabled. The
“PWR” LED will be turned on when the input
source is sufficient to begin charging. The “PWR”
LED will be turned off when the input source is not
present or the input source is below the under
voltage lockout threshold (Typically 4.2V for AC
adapter and 4V for USB inputs).
The charge currents for both USB and AC adapter
charging modes and termination current setting
can be easily adjusted by changing the program
resistors. Please refer to the LTC4075X datasheet
for more information.
Design files for this circuit board are available.
Call the LTC factory.
________________________________________________
LTC is a trademark of Linear Technology Corporation
Table 1.
Performance Summary (T
A
= 25°C unless otherwise noted)
PARAMETER FOR LED DRIVER
CONDITION
VALUE
Input Voltage Range AC adapter and USB
4.3V to 6V
Output Float Voltage VBAT (constant voltage mode)
Over The Full Operating Temperature
Range (0
°
C to 85
°
C)
4.2V +/- 1%
Charge Current AC adapter
R4 = 1.24K
800mA
Charge Current USB Input
R3 = 2.10K
476mA (500mA max, 0
°
C to
85
°
C)
Charge Termination
R5 = 2.00K
50mA