QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 920
STAND ALONE LI-ION CHARGER WITH SYNCHRONOUS BUCK REGULATOR
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LTC4080
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
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
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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
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Figure 1. Demonstration Circuit Test Setup
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
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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
V
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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