QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 551
LITHIUM-ION BATTERY CHARGER WITH CHARGE TERMINATION
3
*Battery Simulator consists of;
Battery Simulator
A battery simulator can be very useful for
evaluating a battery charger. A simple battery
simulator consists of a lab power supply with
coarse and fine (or a multi-turn) voltage adjust
controls and a power resistor connected to the
power supply output terminals. With the resistor
load connected, the power supply can source and
sink current, similar to an actual battery. Any level
of charge from a fully discharged to fully charged
battery can be quickly simulated by simply
changing the battery simulator power supply
voltage. A fully discharged Li-Ion cell will be
approx. 2.6V to 3V and a fully charged cell will be
either 4.1V or 4.2V depending on the battery
chemistry. When the cell is nearly fully charged,
small changes in battery voltage will result in large
changes in charge current.
Of course, there are times when an actual battery is
needed, for example when plotting a complete
charge cycle from start to finish.
QUICK START PROCEDURE
With both power supplies set to 0V, connect the
demo board to power supplies and meters as
shown in Figure 1. The electrical connections
between the charger output and the battery
simulator must be high quality and a 0.1
Ω
sense
resistor is recommended for the charge current
measurement. The dc resistance in the charge
current path should be kept to a minimum.
Undervoltage Lockout and Trickle Charge - After
placing jumper (JP1) in the “RUN” position, begin
increasing the input power supply voltage. At
approximately 4.3V, the LTC4002 undervoltage
lockout will allow the charger to start and the
charge current will abruptly rise to approximately
300mA (30mV on the meter). This is the trickle
charge current for a deeply discharged battery (V
BAT
< 2.9V). Adjust the input supply to approximately
6V.
Trickle Charge Threshold and Constant Current
Charge - Begin increasing the battery simulator
power supply (V
BAT
), observing the charger output
voltage on the DVM. When the voltage exceeds
approximately 2.9V, the charger will suddenly enter
the Constant Current portion of the charge cycle
resulting in an abrupt increase in charge current to
the programmed value of approximately 3A (300mV
on the charge current DVM). This is the constant
current mode. The CHRG LED will also turn on.
Constant Voltage Charge and CHRG LED Indicator -
Continue slowly increasing the battery simulator
power supply, thus simulating a battery accepting
charge. The charge current should remain at the
programmed value of 3A until the charger output
voltage is within approximately 10mV of the preset
charge voltage (4.2V ±1%), at which time the charge
current will begin to decrease. This is the beginning
of the Constant Voltage portion of the charge cycle.
Continue very slowly increasing the battery
simulator power supply until the CHRG LED turns
off, and note the charge current level when it went
off. The current level should be approximately
750mA ±25%. The LED is an indicator that the
battery is approaching full charge. It is not a charge
complete indication. The charge cycle will continue
until the 3 hour timer ends. (Note: when the LED
Power supply with coarse and fine output voltage adjust controls 0 to 5V @ 6A
Power resistors (preload for power supply) 3ea 2
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10W
