Linear Technology DC708 Manuale utente

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC708

LITHIUM-ION LINEAR BATTERY CHARGER WITH THERMAL REGULATION

LTC4064EMS-4.0



Demonstration circuit DC708 is a complete constant-

current, constant-voltage battery charger designed to

charge one Lithium-Ion cell used in battery backup ap-

plications or applications that require greatly increased

cycle life at the expense of battery capacity. The

LTC4064EMS-4.0 used on this demo circuit features an

internal P-channel power MOSFET with a unique thermal

feedback loop that reduces the output current under

high ambient temperature and/or high power dissipation

conditions. This feature allows the charger to provide

higher charge currents under normal conditions and still

provide safe charging under abnormal conditions such

as high ambient temperature, high input voltage or low

battery voltage. The IC is available in a 10-pin MSOP

thermally enhanced package featuring an exposed bot-

tom-side metal pad for soldering to the PC board.

Other Features include:

•

Preset float voltage of 4.0V±1%.

•

Greatly increased cycle life when used for charging

4.1V or 4.2V batteries.

•

1A and 0.5A Constant Current selected by a jumper.

•

Capable of charging directly from USB power.

•

3-hour charge termination timer. This timer can be set

for other time periods through a capacitor change.

For instance, you may want to use a much shorter pe-

riod (on the order of 30 seconds) when evaluating the

board with a battery simulator instead of a real Li-Ion

battery.

•

Charge Current Monitor Output can be used for gas

gauging.

•

Manual Shutdown

•

Low battery drain current when input supply is re-

moved

•

No isolation diode or current sense resistor required.

•

C/10 Trickle charge for deeply discharged batteries

•

Auto recharge when battery voltage drops below pre-

set threshold

•

Input Power OK LED indicator (ACPR)

•

C/10 Charge LED indicator (CHRG)

•

Fault LED indicator for “out of temp range” (FAULT)

Small surface mount components are used to minimize

board space and height with the circuitry occupying ap-

proximately 0.15 square inches of board space with a

height of 0.054 inches (1.4mm).

Table 1. Typical Demo Board Specifications

Input Voltage Range V

4.25V to 7V (upper

range limited by PC

board dissipation)

Output Voltage V

BAT

(constant

voltage mode)

4.0V ±1%

Output Current I

BAT

(constant

current mode)

1 A ± 8%, 0.5A ± 8%

••••••••••••••••••(se

lected by jumper)

Current Monitor Output

1.5V

±5% @ Full Cur-

rent

Output Current I

BAT

(trickle

current mode)

100mA ± 20%, 50mA ±

20%

C/10 CHRG LED Threshold Level

100mA ± 25%. 50Ma ±

25%

Circuit Board Temperature in

Thermal Feedback Mode

60°C to 70°C

Trickle Charge Threshold

Voltage

2.457V

Battery Drain Current with

Removed

<1µA

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC708

LITHIUM-ION LINEAR BATTERY CHARGER WITH THERMAL REGULATION

     



To save time, we recommend using a battery simulator

(described in Table 2 and Figure 1•) If an actual re-

chargeable Li-Ion battery is used, keep the DC resistance

between the charger and the battery to a minimum, as

this will affect the charge current in the constant voltage

mode.

Table 2. Test Equipment Required for Demo Board Evaluation

Lab Power supply for input power 0 to 7V, 1.2A

Digital voltmeter for measuring

input voltage (VIN)

3 1/2 digits

Digital voltmeter for measuring

battery voltage (VBAT)

4 1/2 digits, resolution to 1mV

Digital voltmeter for measuring

PROG pin voltage (current moni-

tor)

3 1/2 digits, resolution to 1mV

Digital voltmeter for measuring

voltage across current sense resis-

tor (IBAT)

100mV range

4.2V Rechargeable Li-Ion Cell or

Battery Simulator

600mA/Hr to 1.3A/Hr

Battery Simulator Consists of:

Power supply with coarse and fine

output voltage adjust controls

0 to 5V, 2.5A

Power resistor (preload for power

supply)

Ω

, 10W

Current sense resistor for measur-

ing charge current

0.1

Ω

, 1%, 1W

Current sense resistor for measur-

ing battery drain current

1k, 1%, 0.5W

SETUP

Refer to Table 2 and Figure 1 for equipment require-

ments and proper setup.

Set jumper JP1 to the “RUN” position (lower posi-

tion).

Set jumper JP2 to the lower position, which programs

the constant charge current to 1A.

Set the input power supply to 0V, and then connect it

to the VIN and GND pins of the demo board.

Set the battery simulator to 0V, and then connect it to

the BAT and GND pins.

Connect the digital voltmeters as shown in the setup

diagram to measure VIN, V(current monitor), charge

voltage (VBAT) and the charge current (IBAT).

EVALUATION

Undervoltage Lockout Feature

•

Increase the input power supply to approximately

3.8V (battery simulator power supply set for 0V).

The charger output voltage and charge current should

be 0. All three LEDs should be off. The charger is in

shutdown due to the undervoltage lockout feature.

Trickle Charge Current

•

Increase the input voltage to 5V and keep the battery

simulator power supply at 0V.

The CHRG and ACPR LEDs should now be on, and the

FAULT LED should be off.

The charger output voltage

(VBAT) should be approximately 240mV, and the

charge current should be about 100mA (10mV on the

charge current DVM). This is the trickle charge mode

for a deeply discharged battery. Typically, a battery

that has not been charged for a long time.

Constant Current Charge

•

Starting at 0V, slowly increase the battery simulator

power supply (VBAT), observing the charger’s output

voltage on the DVM.

When the charger’s output voltage exceeds approxi-

mately 2.45V, the charger will suddenly enter the con-

stant current portion of the charge cycle, resulting in

an abrupt jump in the charge current to the pro-

grammed value of approximately 1.0A (100mV on the

charge current DVM). This is constant current mode.

Move jumper JP2 to the upper position (0.5A) to re-

duce the charge current (IBAT) to 500mA, resulting in

a reading of approximately 50mV on the charge cur-

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC708

LITHIUM-ION LINEAR BATTERY CHARGER WITH THERMAL REGULATION

rent DVM. Move the jumper back to the original posi-

tion.

VPROG Verification

•

With 1.0A charge current flowing into the battery

simulator, measure the current monitor pin voltage

VPROG. This voltage is proportional to charge current

with 1.5V indicating full programmed current (1.0A).

Constant Voltage Charge

Continue slowly increasing the battery simulator

power supply, thus simulating a battery accepting

charge.

The charge current should remain at the programmed

value of 1.0A until the charger output voltage is within

approximately 10mV of the of the preset charge volt-

age (4.0V), at which time the charge current will be-

gin to decrease. This is the beginning of the constant

voltage portion of the charge cycle.

Continue slowly increasing the battery simulator

power supply until the charge current drops to ap-

proximately 200mA (20mV on the charge current

DVM), then read the charger output voltage. This

reading is the charger float voltage which should be

4.0V±40mV.

Shutdown

Move the SHDN/CHRG jumper JP1 to the upper posi-

tion.

This shuts the charger down dropping the charge cur-

rent to 0mA. This is the shutdown mode.

Move the jumper back to the original location.

Charge LED, C/10 Charge Near Complete

•

Continue to slowly increase the battery simulator

power supply while observing the CHRG LED. The

LED will go out when the charge current drops to ap-

proximately 10% of the programmed charge current

of 1.0A. This verifies that the C/10 output is operating

correctly.

NOTE: The LED current drops from approximately

10mA when the LED is on, to approximately 25µA

when the charge current drops to 10%, and drops to

0µA after the timer has timed out. (3 hours when a

0.1µF timing capacitor is used).

At C/10, when the CHRG LED goes out, a 4.2V battery

is about 60% charged. The charger will continue

charging for 3 hours (0.1µF timing capacitor) then

stop, at which point the battery is approximately 68%

charged.

NOTE: Charging a 4.2V Li-Ion battery at 4.0V will de-

crease the mah capacity of the battery to approxi-

mately 68%, but will extend the battery cycle life to

many thousands of cycles, possibly 10,000 or more

cycles.

Recharge

•

After the timer has timed out, slowly decrease the

battery simulator power supply. At around 3.9V, the

1.0A charge current should return. This is the Re-

charge Threshold Voltage.

NOTE: For evaluation purposes, the time can be de-

creased from the programmed 3 hours to approxi-

mately 30 seconds by reducing the timer capacitor

(C3) from 0.1µF to 270pF.

Sleep Mode

•

To verify battery drain current in the sleep mode, re-

move the input supply voltage or shut the supply off,

replace the 0.1

Ω

current sense resistor with a 1k

Ω

and set the battery simulator power supply to ap-

proximately 3.9V. The charge current DVM will now

read battery drain current with 1mV/µA.

NOTE: On this demo board, the thermistor (R6) is re-

placed with a 10k

Ω

resistor. Because the board can

get quite hot, the thermistor must be located near the

battery, not on the pc board.

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC708

LITHIUM-ION LINEAR BATTERY CHARGER WITH THERMAL REGULATION

Thermal Control Loop

Increase the input voltage to about 6.5V, and reduce

the battery simulator power supply to around 3V.

This causes increased power dissipation, which raises

the LTC4064 junction temperature. When the junction

temperature reaches approximately 105°C, the charge

current decreases enough to maintain the junction

temperature at 105°C.

Increase the battery simulator voltage or reduce the

input voltage to reduce the charger power dissipation

and allow the charge current to return to the pro-

grammed current of 1A.

Figure 1.

Proper Measurement Equipment Setup

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC708

LITHIUM-ION LINEAR BATTERY CHARGER WITH THERMAL REGULATION

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DC708A

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