Linear Technology DC937A Manuale utente

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC937A

USB POWER SOLUTION IN DFN 3X4

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

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

= 5V, Vbat=3.6V 700mA +/- 7%

Float Voltage Vin = 5V, battery disconnected from BATT pin 4.20V+/- 35mV

Trickle Charge Threshold V

= 5V 2.9V +/-0.1V

Recharge Threshold V

= 5V (Vfloat – 130mV) to (Vfloat-60mV)

USB Current

Input Current 500mA Mode V

= 5V, USB Active 500mA Mode 475mA typical, 500mA max

Input Current 100mA Mode V

= 5V, USB Active 100mA Mode 93mA typical, 100mA max

Input Current Suspend Mode V

=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:

Connect input power supply, meters and output load

as shown in Figure 1.

USB Charging

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

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC937A

USB POWER SOLUTION IN DFN 3X4

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.

Now increase the load on the SYSTEM LOAD OUTPUT

OUT

). 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 posi-

tion and note that the USB current falls to under

300uA to comply with the USB suspend mode cur-

rent.

Adapter Charging

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.

Note that the charge current to the battery has in-

creased to 700mA.

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

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.

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC937A

USB POWER SOLUTION IN DFN 3X4

Figure 1. Proper Measurement Equipment Setup

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC937A

USB POWER SOLUTION IN DFN 3X4

Mouser Electronics

Authorized Distributor

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DC937A

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