Linear Technology DC937A, LTC4085 Quick Start 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

in faster charging and lower power loss than the charger
fed topology. All this functionality consumes less than
56mm2 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.

uses the intermediate bus voltage topology that results

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)

USB Current

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

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

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

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.

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, I
70mA. Increase the battery voltage to about 2.9V. The

is around

BAT

1

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC937A

USB POWER SOLUTION IN DFN 3X4

battery charge current (I
Note that the input current from the USB (I

) will increase to 475mA.

BAT

) does

USB

not exceed the USB spec of 500mA.

3.

Now increase the load on the SYSTEM LOAD OUTPUT
(I

). Note that as the output load is increased the

OUT

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 posi­tion and note that the USB current falls to under
300uA to comply with the USB suspend mode cur­rent.

Adapter Charging

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.

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.

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.

2