QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 789
SINGLE CELL LI-ION BATTERY CHARGER WITH COMPARATOR
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LTC4062
DESCRIPTION
Demonstration circuit 789 is a complete constant-
current, constant-voltage battery charger for one
Lithium-Ion cell and includes a comparator which can
be used to monitor battery voltage or other voltages.
The LTC4062EDD used on this demo circuit features
an internal P-Channel power MOSFET with a unique
thermal feedback loop that reduces the output current
under high ambient temperature and/or high power
dissipation conditions. This feature allows the charger
to provide higher charge currents under normal con-
ditions and still provide safe charging under abnormal
conditions such as high ambient temperature, high
input voltage or low battery voltage.
Jumpers on the board allow charge currents from
50mA to 1A to be programmed and several charge
termination methods to be used. A jumper also se-
lects either the battery voltage or an external voltage
for the comparator input. Terminals are provided for
the comparator input and output, shutting down the
charger, monitoring charge current and programming
the minimum charge current level for termination
(IDETECT). Two LEDs are included, one indicates
when the charge current has dropped below the
minimum charge current termination level and the
second indicates the comparator output state.
The IC is available in a 10-Pin 3mm x 3mm DFN
thermally enhanced package featuring an exposed
bottom-side metal pad for soldering to the PC board.
Design files for this circuit board are available. Call
the LTC factory.
LTC is a trademark of Linear Technology Corporation
Table 1. Typical Specifications (25°C)
Input Voltage Range VIN 4.3 to 8V (upper range limited by PC board power
dissipation)
Input UnderVoltage Lockout 3.8V
Output Float Voltage VBAT (constant voltage mode) 4.2V ±0.5%
Output Current IBAT (constant current mode) From 50mA to 1A ± 8% (selected by jumpers)
Current Monitor Output 1V ±5% @ Full Current
Charge Termination Timer 3 Hours ±10%
Charge Termination Threshold Current (IDETECT) 25mA, 50mA, 100mA ± 10%
Comparator Threshold 2.910V ±3%
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 789
SINGLE CELL LI-ION BATTERY CHARGER WITH COMPARATOR
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OPERATION
Demonstration circuit 789 allows three methods of
charge termination which are selected using jumper
JP1. In the lower “TIMER” position, the charge cy-
cle terminates at the end of the timer period as set
by capacitor C2. The 3 hour timer is sufficient time
to fully charge a depleted battery when charging at
a current level ranging from C/2 to 1C.
The upper “ITERM” position selects minimum
charge current termination (IDETECT). This method
terminates the charge cycle when the charge cur-
rent drops to a programmed threshold level after
the battery has reached the constant voltage portion
of the charge cycle. Placing the jumper (JP1) in the
middle position defeats the on board termination
thus allowing external user termination.
The charge current and the termination current are
selected using a combination of jumpers JP2, JP3
and JP4. (See table 2)
Table 2. Jumper Positions for Charge Current and Termination Current.
IDET JUMPER (JP4)
100MA C / 10
ICHG-1
(JP3)
ICHG-2
(JP2)
Charge Current Idetect Current Charge Current Idetect Current
C 1A 100mA 500mA 50mA
HIGH C / 5 200mA 100mA 100mA 50mA
C 500mA 100mA 250mA 25mA LOW
C/5 100mA 100mA 50mA 25mA
The CHRG LED always indicates the presence of
charge current that is greater than the IDETECT cur-
rent level that is selected by the IDET jumper (JP4).
The LED is on for charge current greater than IDET,
regardless of the termination method used as set by
jumper JP1.
When minimum charge current termination
(IDETECT) is used, the charge cycle ends when the
Charge current drops below the IDETECT level. The
CHRG LED also goes off.
The CURRENT MONITOR 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. This terminal can also be
used to program other charge currents by removing
jumper JP3 and connecting an external program-
ming resistor from the CURRENT MONITOR termi-
nal to ground.
The COMP IN terminal is connected to the com-
parator’s non-inverting input when selected using
the COMP jumper (JP5 upper position) and COMP
OUT is the open drain comparator output. The
comparator output also drives the COMP LED. The
comparator monitors the battery voltage when
jumper (JP5) is in the BAT (lower) position. See
data sheet for details.
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 789
SINGLE CELL LI-ION BATTERY CHARGER WITH COMPARATOR
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QUICK START PROCEDURE
The charger can be evaluated using an actual Lith-
ium Ion battery or a battery simulator. The battery
simulator is faster because all battery state-of-
charge conditions can be quickly simulated.
A battery simulator consists of an adjustable power
supply with a load resistor across the power supply
output. The resistor value is selected that will pro-
vide approximately 1A when the power supply is set
for 2.5V and the power supply must provide at least
1.7A when adjusted for 4.2V. For this battery simu-
lator, a 2.5 Ohm, 10 Watt power resistor connected
to the output of a 5V, 2A bench supply will work fine.
The power supply can now sink and source current,
similar to a battery, and by changing the power sup-
ply voltage, any battery state-of-charge condition
can be quickly simulated.
Begin evaluation by moving the jumpers to the fol-
lowing positions. Move the TERMINATION METHOD
jumper (JP1) to the ITERM (upper) position to select
minimum charge current termination. Move the IDET
jumper (JP4) to the 100mA (lower) position, the
ICHG-2 jumper (JP2) to the “C” (upper) position and
the ICHG-1 jumper (JP3) to the HIGH (upper) posi-
tion. For this evaluation place the COMP jumper
(JP5) in the BAT (lower) position. The charger is
now set to charge at 1A and use minimum charge
current (IDET = 100mA) for charge termination. The
comparator is set to monitor the battery voltage and
to indicate when the battery voltage drops below
2.910V.
With the input power supply and battery simulator
power supply adjusted to 0V, connect the input
power supply output to the VIN and GND, and the
battery simulator power supply output to the BAT
and GND terminals as shown in Figure 1. An amme-
ter or 100m current sense resistor can be placed
between the BAT terminal and the positive terminal
of the battery simulator to measure charge current.
Connect a 4½ digit DVM to the BAT and GND termi-
nals to measure battery voltage. Begin increasing
the input supply voltage, up to 5V. At approximately
3.8V (undervoltage lockout threshold), the CHRG
LED will turn on and the preconditioning trickle
charge of 100mA (10% of the programed current)
will begin flowing. The COMP LED will be off be-
cause the battery voltage is below 2.910V. Adjust the
battery simulator power supply to 3V. At approxi-
mately 2.9V, the charge current will abruptly in-
crease to the programmed constant current of 1A.
Continue slowly increasing the battery simulator
power supply, thus simulating the Li-Ion battery ac-
cepting charge. As the battery simulator approaches
the float voltage of 4.200V, the charge current will
begin to drop as the charger begins the constant
voltage portion of the charge cycle. It is important to
keep the DC resistance between the charger output
and the battery to a minimum, otherwise the charge
current will begin dropping much sooner. When the
charger is in the constant voltage portion of the
charge cycle, small changes in the simulator power
supply voltage will result in relatively large changes
in charge current. When the charge current drops
below the IDET threshold of 100mA, the charge cur-
rent will drop to 0, the CHRG LED will go off and the
charge cycle will end. When timer termination is se-
lected (using JP1), the CHRG LED will go off when
the charge current drops below 100mA, but the
charge cycle will continue until the 3 hour timer
ends.
After the charge cycle has ended, if the battery volt-
age drops approximately 100mV, a recharge cycle
will begin. A recharge cycle is 50% (1.5 hours) of
the programmed time (provided timer termination is
selected). Reducing the battery simulator down to
approx. 2.910V will result in the comparator to
change states (LED off). The micropower compara-
tor receives power from the battery allowing the
comparator to be active when input power is re-
moved. Other voltages can be monitored by placing
the COMP jumper (JP5) in the EXT (upper) position
and applying the voltage to be monitored to the
COMP IN pin. The internal comparator reference
voltage is 1.00V ± 1.2%, with 50mV of hysteresis.
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 789
SINGLE CELL LI-ION BATTERY CHARGER WITH COMPARATOR
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ADDITIONAL COMMENTS
The charger can be put into a low quiescent current
shutdown mode by pulling the ENABLE terminal
high.
Jumpers JP2, JP3 and JP4 interact with each other
when programming charge current.
Other charge currents can be programmed by re-
moving Jumper JP3 and adding a suitable external
resistor from the CURRENT MONITOR terminal to
ground (Note that the position of JP2 and JP4 will
also determine charge current).
Likewise, other minimum charge current termina-
tion levels can be selected by selecting a suitable
resistor for R5.
The internal termination can be defeated by moving
jumper JP1 to the center position. Charge termina-
tion is then left to the user through the ENABLE
terminal.
When the minimum charge current termination
method is used and no battery is present, a
sawtooth waveform of several hundred mV p-p will
appear at the charger output. This is a function of
the output capacitor and the charger output voltage
cycling between the recharge threshold voltage and
the float voltage. The sawtooth frequency is de-
pendant on the value of the output capacitor. With a
2.2µF output capacitor, the frequency is approxi-
mately 40Hz, which will cause the CHRG LED to
appear dim. With a larger output capacitor, the LED
will flash briefly.
To speed up the 3 hour timer when evaluating the
charger circuit, replace the timing capacitor with a
much smaller value. A 300pF capacitor will reduce
the total time to approx 30 seconds.
The one Ohm resistor in series with the ceramic
input capacitor is used to minimize transient volt-
ages caused by the capacitor when the input volt-
age is quickly applied.
See LTC4062 Data Sheet for additional informa-
tion.
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 789
SINGLE CELL LI-ION BATTERY CHARGER WITH COMPARATOR
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Figure 1. Demo Circuit Hookup and Jumper Information
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 789
SINGLE CELL LI-ION BATTERY CHARGER WITH COMPARATOR
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