Linear Technology DC708 Quick Start Manual page 3

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
1.
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
2.
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-
1.
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.
2.
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 0.1Ω current sense resistor with a 1kΩ,
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 10kΩ resistor. Because the board can
get quite hot, the thermistor must be located near the
battery, not on the pc board.
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