DEMO BOARD QUICK START GUIDE DC454
LITHIUM-ION LINEAR BATTERY CHARGER WITH THERMAL REGULATION
LTC1733
DESCRIPTION
Demonstration board DC454 is a complete constant-
current, constant-voltage battery charger designed to
charge one Lithium-Ion cell. The LTC1733 used on this
demo board features an internal P-channel power
MOSFET with a unique thermal feedback loop that re-
duces the output current under high ambient tempera-
ture and/or high power dissipation conditions. This fea-
ture allows the charger to provide higher charge cur-
rents under normal conditions and still provide safe
charging under abnormal conditions such as high ambi-
ent temperature, high input voltage or low battery volt-
age. The IC is available in a 10-pin MSOP thermally en-
hanced package featuring an exposed bottom-side metal
pad for soldering to the PC board.
Other Features include:
•
Preset float voltages of 4.1 and 4.2V±1% (DC364A-A)
•
1.24A Constant Current (can be programmed for
other charge currents up to 1.5A)
•
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.
•
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
IN
Output Voltage V
BAT
(constant voltage
mode)
Output Current I
BAT
(constant current
mode)
4.7V to 7V (upper range lim-
ited by PC board dissipation)
4.1 or 4.2V ±1% selected by
jumper
1.24A ± 8%
Output Current I
BAT
(trickle current mode) 120mA ± 20%
C/10 CHRG LED Threshold Level
Circuit Board Temperature in Thermal
Feedback Mode
Trickle Charge Threshold Voltage
Battery Drain Current with V
IN
Removed
125mA ± 25%
80°C to 85°C
2.457V
<1µA
1
DEMO BOARD QUICK START GUIDE DC454
LITHIUM-ION LINEAR BATTERY CHARGER WITH THERMAL REGULATION
QUICK START PROCEDURE
To save time, we recommend using a battery simulator
(described in Table 2 and Figure 1) If an actual recharge-
able Li-Ion battery is used, keep the DC resistance be-
tween 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
Digital voltmeter for measuring in-
put voltage (V
IN
)
0 to 7V, 1.5A
3½ digits
4.
Set
the battery simulator to 0V, and then connect it to
the BAT and GND pins.
the digital voltmeters as shown in the setup
diagram to measure V
IN
, V
PROG
, charger voltage
(V
BAT
) and the charge current (I
BAT
).
5.
Connect
EVALUATION
Undervoltage Lockout Feature
•
Increase the input power supply to approximately
4.0V (battery simulator power supply set for 0V).
The charger output voltage and charge current should
be 0. The CHRG and ACPR LEDs should be off, and
the FAULT LED should be on. The charger is off due to
the undervoltage lockout feature.
Trickle Current Charge
•
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
(V
BAT
) should be approximately 300mV, 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
Digital voltmeter for measuring bat- 4½ digits, resolution to 1mV
tery voltage (V
BAT
)
Digital voltmeter for measuring
PROG pin voltage
3½ digits, resolution to 1mV
Digital voltmeter for measuring
100mV range
voltage across current sense resis-
tor (I
BAT
)
4.1 or 4.2V Rechargeable Li-Ion Cell or Battery Simulator
Battery Simulator Consists of:
Power supply with coarse and fine
output voltage adjust controls
Power resistor (preload for power
supply)
Current sense resistor for measur-
ing charge current
Current sense resistor for measur-
ing battery drain current
0 to 5V, 2.5A
2Ω, 10W
0.1Ω, 1%, 1W
1k, 1%, 0.5W
SETUP
Refer to Table 2 and Figure 1 for equipment require-
ments and proper setup.
1.
Set jumper
•
Starting at 0V, slowly increase the battery simulator
power supply (V
BAT
), observing the charger’s output
voltage on the DVM.
When the charger’s output voltage exceeds approxi-
mately 2.4V, 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 1.24A (124mV on
the charge current DVM). This is constant current
mode.
JP1 to select the voltage of the cell.
For 4.2V cell, JP1 should be between the center pin
and the top pin; for a 4.1V cell it should be connected
to the center and the bottom pin.
2.
Set
3.
Set
jumper JP2 to the upper position, which enables
the circuit.
the input power supply to 0V, and then connect it
to the V
IN
and GND pins of the demo board.
2
DEMO BOARD QUICK START GUIDE DC454
LITHIUM-ION LINEAR BATTERY CHARGER WITH THERMAL REGULATION
V
PROG
Verification
•
With 1.24A charge current flowing into the battery
simulator, measure the program pin voltage V
PROG
.
This voltage is proportional to charge current with
1.5V indicating full programmed current (1.24A).
Constant Voltage Charge
1.
Continue
At C/10, when the CHRG LED goes out, the battery is
about 94% charged. The charger will continue charg-
ing for 3 hours (0.1µF timing capacitor) then stop, at
which point the battery is 100% charged.
Recharge
•
After the timer has timed out, slowly decrease the
battery simulator power supply. At around 3.95V
(with jumper JP1 in the 4.2V position), the 1.24A
charge current should return. This is the Recharge
Threshold Voltage.
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.
NOTE:
slowly increasing the battery simulator
power supply, thus simulating a battery accepting
charge.
The charge current should remain at the programmed
value of 1.24A until the charger output voltage is
within approximately 10mV of the of the preset
charge voltage, at which time the charge current will
begin to decrease. This is the beginning of the con-
stant voltage portion of the charge cycle.
Sleep Mode
•
To verify battery drain current in the sleep mode, re-
move the input supply voltage or shut the supply off,
replace the 0.1Ω current sense resistor with a 1kΩ,
and set the battery simulator power supply to ap-
proximately 4V. The charge current DVM will now
read battery drain current with 1mV/µA.
On this demo board, the thermistor (R6) is re-
placed with a 10kΩ resistor. Because the board can
get quite hot, the thermistor must be located near the
battery, not on the pc board.
NOTE:
2.
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 will be ei-
ther 4.1V±40mV or 4.2V±40mV depending on the
location of the SELECT jumper.
Shutdown
1.
Move
the SHDN/CHRG jumper JP2 to the center and
lower pins.
The charger shuts down dropping the charge current
to 0mA. This is the shutdown mode.
Thermal Control Loop
1.
Increase
2.
Move the jumper back to the original location.
the input voltage to about 6.5V, and reduce
the battery simulator power supply to around 2.8V.
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 1.24A. This verifies that the C/10 output is operat-
ing correctly.
The LED current drops from approximately
10mA when the LED is on, to approximately 50µA
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).
NOTE:
This causes increased power dissipation, which raises
the LTC1733 junction temperature. When the junction
temperature reaches approximately 105°C, the charge
current decreases enough to maintain the junction
temperature at 105°C. (Printed circuit board tempera-
ture will be approximately 82°C).
2.
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 1.24A.
3
DEMO BOARD QUICK START GUIDE DC454
LITHIUM-ION LINEAR BATTERY CHARGER WITH THERMAL REGULATION
MEASURE CHARGE CURRENT (I
BAT
)
+
–
LI-ION BATTERY SIMULATOR
0.1Ω
1%
+
BATTERY
SIMULATOR
BENCH
POWER SUPPLY
0V–4.3V
2.5A
WITH COURSE
AND FINE
VOLTAGE
ADJUSTMENT
+
–
+
V
PROG
TO MONITOR
CHARGE CURRENT (I
BAT
)
Figure 1. Proper Measurement Equipment Setup
DROP IN CHARGE CURRENT IS DUE TO THE
THERMAL FEEDBACK LOOP LIMITING THE
JUNCTION TEMPERATURE TO 105˚C
4.5
BATTERY VOLTAGE
1.4
CHARGE CURRENT (A)
4.0
BATTERY VOLTAGE (V)
3.5
3.0
CHARGE CURRENT
2.5
80˚
60˚
40˚
TIMER ENDS
PC COPPER TEMP
2.0
1.5
1.0
0.5
180
1.2
1.0
0.8
0.6
0.4
0.2
0
20˚
CHRG LED OFF
30
60
90
120 150
CHARGE TIME (MINUTES)
DEMO BOARD DC454A
2" x 2" 4-LAYER PC BOARD
AMBIENT TEMP = 25˚C
V
IN
= 5.2V
CHARGE CURRENT = 1.24A
18650 LI-ION 1300mA/Hr
Figure 2. Typical Li-Ion Charge Profile
–
–
INPUT POWER
SUPPLY
0–7V
1.5A
DO NOT
EXCEED 7V
V
BAT
+
2Ω
10W
PRELOAD
+
–
–
4
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