QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC937A
USB POWER SOLUTION IN DFN 3X4
1
LTC4085
DESCRIPTION
Demonstration circuit DC937A is a complete power con-
troller for a USB powered device. It is based on the
LTC4085 and provides the following functions: 700mA
CC/CV timer terminated temperature qualified charger
suitable for Li-Ion cells, a USB power manager that in-
sures compliance with the USB power specification and
power path management for the battery. The LTC4085
uses the intermediate bus voltage topology that results
in faster charging and lower power loss than the charger
fed topology. All this functionality consumes less than
56mm
2
of PCB area.
Design files for this circuit board are available. Call
the LTC factory.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Table 1.
Performance Summary
PARAMETER
CONDITION
VALUE
Input Voltage
4.5V - 5.5V
Battery Charger
Iout
V
IN
= 5V, Vbat=3.6V
700mA +/- 7%
Float Voltage
Vin = 5V, battery disconnected from BATT pin
4.20V+/- 35mV
Trickle Charge Threshold
V
IN
= 5V
2.9V +/-0.1V
Recharge Threshold
V
IN
= 5V
(Vfloat – 130mV) to (Vfloat-60mV)
USB Current
Input Current 500mA Mode
V
IN
= 5V, USB Active 500mA Mode
475mA typical, 500mA max
Input Current 100mA Mode
V
IN
= 5V, USB Active 100mA Mode
93mA typical, 100mA max
Input Current Suspend Mode
V
IN
=5V, USB Suspend
300uA max
OPERATING PRINCIPLES
DC937A is the demo board for LTC4085. This chip
manages the power supplies that would be typical for a
USB powered device. Power is input from either the
USB cable or an adapter to an intermediate voltage bus.
The intermediate voltage bus is preferentially powered
from the adapter, then USB and finally if required from
the battery via an ideal diode. The battery charger is a
CC/CV timer terminated type capable of charge currents
of up to 1500mA.
QUICK START PROCEDURE
Demonstration circuit DC937A is easy to set up to evalu-
ate the performance of the LTC4085. Refer to Figure 1
for proper measurement equipment setup and follow the
procedure below:
1.
Connect input power supply, meters and output load
as shown in Figure 1.
USB Charging
2.
Place the USB ON/OFF jumper (JP1) in the ON posi-
tion. Place the USB current jumper (JP2) in the
500mA position. Set the battery simulator voltage to
zero, slowly raise the USB input voltage. When the
supply voltage exceeds 3.8V the charger should acti-
vate and the charge LED D2 will illuminate. The bat-
tery will be in trickle charge mode, I
BAT
is around
70mA. Increase the battery voltage to about 2.9V. The
