DC937A - Demo Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC937A
USB POWER SOLUTION IN DFN 3X4
LTC4085
DESCRIPTION
Demonstration circuit DC937A is a complete power controller 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 insures 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
2
56mm 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
VIN = 5V, Vbat=3.6V
700mA +/- 7%
Float Voltage
Vin = 5V, battery disconnected from BATT pin
4.20V+/- 35mV
Trickle Charge Threshold
VIN = 5V
2.9V +/-0.1V
Recharge Threshold
VIN = 5V
(Vfloat – 130mV) to (Vfloat-60mV)
Input Current 500mA Mode
VIN = 5V, USB Active 500mA Mode
475mA typical, 500mA max
Input Current 100mA Mode
VIN = 5V, USB Active 100mA Mode
93mA typical, 100mA max
Input Current Suspend Mode
VIN =5V, USB Suspend
300uA max
USB Current
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 evaluate 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 position. 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 activate and the charge LED D2 will illuminate. The battery will be in trickle charge mode, IBAT is around
70mA. Increase the battery voltage to about 2.9V. The
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC937A
USB POWER SOLUTION IN DFN 3X4
battery charge current (IBAT) will increase to 475mA.
Note that the input current from the USB (IUSB) does
not exceed the USB spec of 500mA.
3.
4.
5.
Now increase the load on the SYSTEM LOAD OUTPUT
(IOUT). Note that as the output load is increased the
charging current is decreased and the USB current
remains within the 500mA limit.
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
Place the USB ON/OFF jumper (JP1) in the OFF position and note that the USB current falls to under
300uA to comply with the USB suspend mode current.
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 increased 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 diode 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 connection 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.
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC937A
USB POWER SOLUTION IN DFN 3X4
Figure 1. Proper Measurement Equipment Setup
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC937A
USB POWER SOLUTION IN DFN 3X4
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