DUAL INPUT LI-ION BATTERY CHARGER WITH SYNCHRONOUS BUCK REGULATOR
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1068A
LTC3550
Demonstration circuit 1068A is a complete sin-
gle cell Lithium-Ion battery charger and a syn-
chronous buck voltage regulator with adjustable
output voltage. Operating at a frequency of
1.5MHz, the regulator can be powered from ei-
ther the Li-Ion battery or from the AC adapter
(selected by a jumper). The battery charger
automatically selects input power from the AC
adapter or USB port, which ever is appropriate.
This demonstration circuit allows the user to
quickly evaluate the LTC3550 performance. In-
dividual jumpers are provided for shutting down
the charger from either input power source,
shutting down the regulator and for selecting
several regulated output voltages.
LEDs indicate charger information (input power
and charge status) and terminals on the board
allow easy hookup to input supplies and battery
or battery simulator. Provisions are provided for
programming and monitoring charge current
Table 1. Typical Specifications (25°
C)
from each input power source individually, pro-
gramming the minimum charge current termina-
tion level and two charge current levels when
charging from USB power.
The high switching frequency of the DC/DC
converter allow tiny LC components to be used
and the 16-Pin 5mm x 3mm DFN thermally en-
hanced package with the metal backside allow
the linear charger to provide up to 950mA of
charge current in addition to the regulators out-
put current. The charge current on this board is
set for either 100mA or 500mA when powered
from USB power and 800mA when used with an
AC adapter.
Design files for this circuit board are available.
Call the LTC factory.
LTC and Burst Mode are trademarks of Linear
Technology Corporation
Adapter and USB Input Voltage Range (
Buck regulator powered from Battery
)
Adapter Input Voltage Range (
Buck regulator powered from Adapter Input
)
Charger Output Float Voltage, VBAT (
constant voltage mode
)
Charge Current, IBAT from Adapter Input (
constant current mode
)
Charge Current, IBAT from USB Input (
constant current mode
) HPWR terminal High/Low
Trickle Charge Current, IBAT from Adapter Input (
Battery Voltage <2.9V)
Adapter and USB Current Monitor Output
Charge Termination Threshold Current
C/x Output Indication Level LED (CHRG)
VOUT Regulator Output Voltage — 1.2V, 1.8V, 2.5V (
100mA Load
)
VOUT Ripple Voltage — (
400mA Load
)
VOUT Ripple Voltage — Burst mode (
Light Load
)
Regulator Maximum Output Current
4.25V to 8V
4.25V to 5.5V
4.2V ±0.5%
800mA ± 6%
500mA/100mA ± 6%
80mA ± 6%
1V ±2.5% @ Full Current
50mA ±10%
50mA ±10%
± 2.5%
18mV p-p
80mV p-p
600mA
1
DUAL INPUT LI-ION BATTERY CHARGER WITH SYNCHRONOUS BUCK REGULATOR
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1068A
The battery charger portion of demonstration
circuit 1068A uses a constant-current/constant
voltage charge algorithm with a programmable
minimum charge current termination. The bat-
tery float voltage is fixed at 4.2V and the
charge current is programmed for 100mA,
500mA or 800mA, depending which power
source is used and the status of the HPWR
terminal. The charge cycle terminates when
the charge current drops below 50mA after
reaching the float voltage. Power and Charge
LEDs indicate charger status. The Power LED
indicates the input voltage from either input
power source is greater than the undervoltage
lockout threshold level and at least 180mV
greater than the battery voltage.
The Charge LED indicates a charge cycle is in
progress. The LED is ON when the charger is
in the trickle current, constant current, or the
constant voltage portion of the charge cycle
(when the charge current is dropping). When
the charge current drops below the charge
termination current threshold level of 50mA,
the LED goes off and the charge cycle ends.
If the battery voltage drops approximately
100mV from the float voltage, after the charge
cycle has ended, a recharge cycle will begin.
With power applied to the adapter input, plac-
ing the EN Jumper (JP1) in the upper position
can shut down the charger. When USB power
is present, the charger can be shut down by
moving the jumper to the middle position. The
lower position enables the charger when either
input is used.
The IDC and the IUSB terminals can be used
to measure the charge current that is being
supplied from either input supply anytime in
the charge cycle. The voltage on these pins is
directly proportional to the charge current
where one Volt is equal to full programmed
current.
The 1.5MHz synchronous buck regulator has
jumpers to select output voltages of 1.2V, 1.8V,
or 2.5V at up to 600mA of output current. Burst
mode operation occurs at low load current and
automatically changes to continuous mode at
high current. Burst mode provides higher effi-
ciency at low load current.
The input power for the buck regulator can be
from either the adapter input or from the bat-
tery, selected by jumper JP2. Note that when
the regulator is powered from the adapter in-
put, the maximum input voltage is limited to
5.5V. Normally, a Li-Ion battery would be con-
nected to the BAT pin, although the buck regu-
lators can be operated without a battery. When
no battery is present, some additional capaci-
tance may be needed on the battery terminal.
2
DUAL INPUT LI-ION BATTERY CHARGER WITH SYNCHRONOUS BUCK REGULATOR
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1068A
-
ADAPTER
+5V
INPUT
POWER
(0 to 5V)
USB
INPUT
POWER
(0 to 5V)
monitor
charge
current
V1
+
+
Regulator
Load
Resistor
+5V
+
V2
V4
V5
(connect to
USB Input)
Charger
Enable
V3
0.1ž
3ž
10W
from USB
from Adapt
-
Regulator
100mA 500mA
Selects power
OFF ON
from USB
source for
regulator
BATTERY
SIMULATOR
POWER
SUPPLY
(0 to 5V)
Battery Simulator
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
Charger Evaluation
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 800mA when the power supply is
set for 2.6V and the power supply must provide
at least 1.4A when adjusted for 4.2V. For this
battery simulator, a 3 Ohm 10 Watt power resis-
tor connected to the output of a 5V, 1.5A bench
supply will work fine.
Begin circuit evaluation by placing the jumpers
to the following positions; JP1 lower, JP2 up-
per, JP3 lower, and place a jumper in the JP4
(1.2V) position. With the input power supply
and battery simulator power supply turned on
and adjusted for 0V, connect the demonstra-
tion circuit as shown in Figure 1. Note: Con-
nect an external wire from the USB input ter-
minal to the HPWR terminal to pull it high.
Adjust the battery simulator power supply to
approximately 2.5V, then begin increasing the
USB input supply up to 5V. At approximately
3.9V (the USB undervoltage lockout threshold),
the Power and Charge LEDs will turn on and a
preconditioning trickle charge of 50mA will be-
gin flowing into the battery simulator. The IUSB
pin voltage (Voltmeter V4) will measure about
100mV indicating 10% of the programmed cur-
rent. Increase the battery simulator power
3
DUAL INPUT LI-ION BATTERY CHARGER WITH SYNCHRONOUS BUCK REGULATOR
supply to 3V as measured by V2. At approxi-
mately 2.85V, the charge current will abruptly
increase to the programmed constant current of
500mA, which is the maximum rated current
available from a USB port. Voltmeter V4, con-
nected to the IUSB terminal, will measure 1 Volt
and V3 will measure 50mV across the 100m
charge current sense resistor indicating the full
500mA charge current is flowing. Remove the
wire connected to the HPWR terminal allowing
the internal pull-down resistor to pull the HPWR
pin low, dropping the charge current to 100mA.
V4 will measure 200mV & V3 will be 10mV.
Adjust the Adapter input supply to 5V. At ap-
proximately 4.15 (the Adapter input undervolt-
age lockout threshold) the charge current will
abruptly increase to the programmed adapter
charge current of 800mA. Voltmeter V4 will be
0V and V5 will now measure 1V indicating full
programmed current from the Adapter input
power supply. Note; reducing the simulator
power supply voltage below the trickle charge
voltage of 2.85V will reduce the charge current
to 10% of the programmed value.
Slowly increase the battery simulator power
supply, thus simulating the Li-Ion battery ac-
cepting charge. As the battery simulator ap-
proaches the float voltage of 4.200V, as meas-
ured 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 portion of the charge cy-
cle, small changes in the simulator power sup-
ply voltage will result in relatively large changes
in charge current. The IUSB and the IDC termi-
nals indicate charge current levels from the re-
spective input power sources at all times during
the charge cycle with 1 Volt indicating 100% of
the programmed current. When the charge cur-
rent drops below the End-of-Charge threshold
of 50mA (programmed by R6), the Charge
LED will go OFF and the charge cycle ends.
Reducing the battery simulator voltage by ap-
proximately 100mV will start a recharge cycle.
When no battery is present, the charger output
will exhibit a sawtooth waveform of several
hundred mV centered on 4.2V. This is a result
of the repeated cycling between charge termi-
nation and recharge threshold. This also
causes the Charge LED to pulse rapidly and
appear to light dimly.
The one-Ohm resistor in series with the ce-
ramic input capacitors minimizes the ringing
and overshoot that appears at the input when
the input voltage is hot switched. Input voltage
transients can easily exceed the maximum rat-
ings causing serious damage to the LTC3550.
Buck Regulator Evaluation
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1068A
Move the DC/DC Power jumper (JP2) to the
ADAPT (lower) position and select the desired
output voltage using jumpers JP4 through JP6.
Place the RUN jumper, JP3 in the ON (upper)
position and connect a suitable load resistor
between the VOUT terminal and GND. The
maximum load current is approximately
600mA. With Adapter input power applied, ver-
ify that the output voltage, as measured by V1
is between the limits as shown in Table 1. A
scope can also be used to measure the regula-
tor output ripple voltage. When evaluating out-
put ripple, observe proper scope probe meas-
uring technique as shown in Figure 3. To in-
crease efficiency at light loads, the regulator
operates in burst mode resulting in higher out-
put ripple voltage. As the load current in-
creases, the output ripple decreases as the
regulator changes to continuous operation.
See LTC3550 Data Sheet for additional information.
4
DUAL INPUT LI-ION BATTERY CHARGER WITH SYNCHRONOUS BUCK REGULATOR
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1068A
20mV/div 200ns/div (400mA load)
V
OUT
GND
50mV/div 20µs/div (burst mode)
Figure 3. Scope Probe Placement for Measur-
ing Output Ripple Voltage
Figure 2. Output Ripple Voltage
5
无线连接
京公网安备 11010802033920号
Copyright © 2005-2026 EEWORLD.com.cn, Inc. All rights reserved
电子工程世界
