Linear Technology LTC4080 User manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 920

STAND ALONE LI-ION CHARGER WITH SYNCHRONOUS BUCK REGULATOR

LTC4080

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Demonstration circuit 920 is a complete single

cell Lithium-Ion battery charger and adjustable

output voltage buck switching regulator. Operat-

ing at a frequency of 2.25MHz, the 300mA syn-

chronous regulator is powered from the Li-Ion

battery.

This demonstration circuit allows the user to

quickly evaluate the LTC4080 performance. In-

dividual jumpers are provided for shutting down

the charger and/or the switching regulator, for

selecting several regulated output voltages and

the mode of operation (fixed frequency or

Burst). LEDs indicate charger status (input

power and charge) and pins on the board allow

easy hookup to an input supply and battery or

battery simulator.

The high switching frequency of the voltage

regulator allow tiny LC components to be used

and the 10-Pin 3mm x 3mm DFN thermally en-

hanced package with the metal backside allow

the linear charger to provide up to 500mA of

charge current in addition to the regulator out-

put current.

Design files for this circuit board are available.

Call the LTC factory.

LTC and Burst Mode are trademarks of Linear Technol-

ogy Corporation

Table 1. Typical Specifications (25°C)

Input Voltage Range VIN 3.75V to 5.5V

Output Charger Float Voltage VBAT (constant voltage mode)

4.2V ±0.5%

Output Current IBAT (constant current mode) 500mA ± 5%

Current Monitor Output 1V ±1.5% @ Full Current

Charge Termination Timer 4.5 Hours ±25%

C/10 Output Indication Level (CHRG) 50mA ± 10%

1.2V Regulator VOUT (100ma) 1.2V ± 2.5%

1.5V Regulator VOUT (100ma) 1.5V ± 2.5%

1.8V Regulator VOUT (100ma) 1.8V ± 2.5%

2.5V Regulator VOUT (100ma) 2.5V ± 2.5%

Regulator Output Ripple Voltage (fixed frequency) 5mV p-p

Regulator Output Ripple Voltage (burst mode) 50mV p-p

Buck Regulator Maximum Output Current (fixed frequency) 350mA

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The battery charger portion of demonstration

circuit 920 uses a constant-current/constant

voltage charge algorithm with timer charge

termination. The battery float voltage is fixed at

4.2V and the charge current is programmed for

500mA, although a lower charge current can

be programmed by replacing the program re-

sistor (R5) with a suitable value. Either a

leaded resistor, from PROG to GND, or a 0402

surface mount resistor can be used.

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 920

STAND ALONE LI-ION CHARGER WITH SYNCHRONOUS BUCK REGULATOR

Power and Charge LEDs indicate charger

status. The Power LED indicates that the input

voltage is greater than the undervoltage lock-

out threshold level.

The Charge LED has three states. With a bat-

tery connected, the LED is on when either

trickle current is flowing (VBAT < 2.9V) or

when charge current greater than 10% of the

programmed value is flowing (VBAT > 2.9V).

When the battery voltage approaches the float

voltage, the charge current will begin to drop.

When it drops below 10%, the Charge LED

goes out, indicating that the battery is near full

charge. Charging continues until the timer

ends the charge cycle. During a trickle charge,

if the battery voltage does not exceed 2.9V af-

ter ¼ of the total charge time, the battery is

considered defective, charging ends and the

Charge LED flashes at a 2Hz rate.

With no battery connected, there is a condition

where the Charge LED will be on with very lit-

tle or no charge current flowing. This occurs

with low input voltage. When the input voltage

exceeds approximately 3.5V, the Power and

Charge LEDs come on. Above 4.3V, the

Charge LED goes off.

The charger jumper (JP1) can be used to shut

down the charger and reset the timer. The

PROG terminal can be used to program differ-

ent charge current and also measure the

charge current anytime in the charge cycle.

The PROG pin voltage is directly proportional

to the charge current where one Volt is equal

to full programmed current.

After the charge cycle has ended, if the battery

voltage drops approximately 100mV, a new

2.25 hour recharge cycle will begin.

The 2.25MHz synchronous buck regulator has

jumper selected output voltages of 1.2V, 1.5V,

1.8V and 2.5V with output current up to

300mA. Jumpers are also provided for low

quiescent current shutdown and for either fixed

frequency or Burst mode operation. Burst

mode provides high efficiency at low load cur-

rent. The input power for the regulator comes

from the BAT pin. Normally, a Li-Ion battery

would be connected to the BAT pin, although

the buck regulator can be operated without a

battery. When no battery is present, some ad-

ditional capacitance on the BAT pin may be

needed. Also, when the termination timer ends,

the BAT voltage will begin to drop. When it

drops below the recharge threshold, the timer

is reset and the charger output voltage returns

to the float voltage of 4.2V.

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 920

STAND ALONE LI-ION CHARGER WITH SYNCHRONOUS BUCK REGULATOR

Figure 1. Demonstration Circuit Test Setup

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The charger section can be evaluated using an

actual Lithium Ion battery or a battery simulator.

The battery simulator is faster because all bat-

tery state-of-charge conditions can be quickly

simulated.

Battery Simulator

A battery simulator consists of an adjustable

power supply with a load resistor across the

power supply output. The load resistor allows

the battery simulator to source and sink current,

similar to an actual battery. Any battery state-of-

charge condition can be quickly simulated by

simply changing the power supply output volt-

age. The load resistor value is selected that will

sink at least 500mA when the power supply is

set for 2.5V and the power supply must provide

at least 850mA when adjusted for 4.2V. For this

battery simulator, a 5 Ohm, 5 Watt power resis-

tor connected to the output of a 5V, 1A bench

supply will work fine.

Battery Charger

Begin circuit evaluation by moving the jumpers

to the appropriate positions. With the input

power supply and battery simulator power

supply adjusted to 0V, connect the demonstra-

tion circuit as shown in Figure 1.

Begin increasing the input supply voltage, up

to 5V. At approximately 3.6V (the undervoltage

lockout threshold), the Power and Charge

LEDs will turn ON and the preconditioning

trickle charge of 50mA will begin flowing into

the battery or battery simulator. The PROG pin

voltage (Voltmeter V1) will measure 100mV

indicating 10% of the programmed current. Ad-

just the battery simulator power supply to 3V

as measured by V2. At approximately 2.9V, the

charge current will abruptly increase to the

programmed constant current of 500mA. Volt-

meter V1 will measure 1 Volt and V3 will

measure 50mV indicating full charge current is

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 920

STAND ALONE LI-ION CHARGER WITH SYNCHRONOUS BUCK REGULATOR

flowing. Continue slowly increasing the battery

simulator power supply, thus simulating the Li-

Ion battery accepting charge. As the battery

simulator approaches the float voltage of

4.200V, as measured by V2, the charge current

will begin to drop as the charger begins the

constant voltage portion of the charge cycle.

When the charger is in the constant voltage por-

tion of the charge cycle, small changes in the

simulator power supply voltage will result in

relatively large changes in charge current. The

PROG terminal can be used to indicate charge

current level at all times during the charge cycle

with 1 Volt indicating 100% of the programmed

current. When the charge current drops below

the End-of-Charge threshold level of 50mA, the

Charge, LED will go OFF indicating the battery

is near full charge. The charge cycle will con-

tinue until the 4.5 hour timer ends.

The one Ohm resistor in series with the ceramic

input capacitor on Vcc minimizes the ringing

and overshoot that appears at the input when

the input voltage is hot switched. Without the

series resistor, serious damage to the LTC4080

can occur. See Figure 2. Pads are also included

for an additional input capacitor. Adding a tan-

talum capacitor at this location will also mini-

mize voltage ringing and overshoot.

Buck Regulator

Select one of the four output voltages using

jumpers JP4 through JP7. (With no jumpers

installed, the output voltage is set to the refer-

ence voltage of 800mV.) With jumpers JP3 in

the fixed frequency position, JP1 and JP2 in

the ON position, connect a suitable load resis-

tor between VOUT and GND terminals. The

maximum load current is approximately

300mA. Verify that the output voltage, as

measured by V4 is between the limits as

shown in Table 1. A scope can also be used to

measure the regulator output ripple voltage.

When evaluating output ripple, observe proper

scope probe measuring technique as shown in

Figure 3. For high efficiency at light load condi-

tions, move jumper J3 to the BURST position.

In Burst mode, the output ripple voltage is

higher (20 - 40mV) and the maximum output

current is approximately 50mA.

See LTC4080 Data Sheet for additional information.

Figure 2. Input Voltage Transient When Input

Power is Hot Switched

OUT

GND

Figure 3. Scope Probe Placement for Measur-

ing Output Ripple Voltage

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 920

STAND ALONE LI-ION CHARGER WITH SYNCHRONOUS BUCK REGULATOR

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