QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 788B
SINGLE CELL LI-ION BATTERY CHARGER WITH NTC
LTC4061-4.4
DESCRIPTION
Demonstration circuit 788B is a complete constant-
current, constant-voltage battery charger for one
Lithium-Ion cell that requires a higher float voltage of
4.375V. The LTC4061EDD-4.4 used on this demo cir-
cuit 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 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
ambient temperature, high input voltage or low bat-
tery voltage.
Jumpers on the board allow charge currents from
50mA to 1A to be programmed and several charge
termination methods to be used. Terminals are pro-
Table 1. Typical Specifications (25°C)
Input Voltage Range VIN
Input UnderVoltage Lockout
Output Float Voltage VBAT (constant voltage mode)
Output Current IBAT (constant current mode)
Current Monitor Output
Charge Termination Timer
Charge Termination Threshold Current (IDETECT)
4.5 to 8V (upper range limited by PC board power
dissipation)
3.8V
4.375V ±0.5%
From 50mA to 1A ± 8% (selected by jumpers)
1V ±5% @ Full Current
3 Hours ±10%
25mA, 50mA, 100mA ± 10%
vided for adding a thermistor for sensing battery
temperature, shutting down the charger, monitoring
charge current and programming the minimum
charge current level for termination (IDETECT). An
LED indicates when the charge current has dropped
below the minimum charge current termination level.
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
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 788B
SINGLE CELL LI-ION BATTERY CHARGER WITH NTC
OPERATION
Demonstration circuit 788B allows three methods
of charge termination which are selected using
jumper JP1. In the lower “Timer” position, the
charge cycle terminates at the end of the timer pe-
riod as set by capacitor C2. The 3 hour timer is suf-
ficient 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 por-
tion of the charge cycle. Placing the jumper (JP1)
in the middle position defeats the on board termi-
nation 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
ICHG-1
(JP3)
HIGH
ICHG-2
(JP2)
C
C/5
C
LOW
C/5
Charge Current
1A
200mA
500mA
100mA
Idetect Current
100mA
100mA
100mA
100mA
C / 10
Charge Current
500mA
100mA
250mA
50mA
Idetect Current
50mA
50mA
25mA
25mA
The CHRG LED always indicates the presence of
charge current that is greater than the IDETECT
current 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 indi-
cate 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 remov-
ing jumper JP3 and connecting an external pro-
gramming resistor from the current monitor termi-
nal to ground. See data sheet for details.
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 788B
SINGLE CELL LI-ION BATTERY CHARGER WITH NTC
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 4.4V. 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 supply voltage, any battery state-of-charge
condition can be quickly simulated.
Begin circuit evaluation by moving the jumpers to
the appropriate 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” (up-
per) position and the ICHG-1 jumper (JP3) to the
HIGH (upper) position. For this evaluation, disable
the NTC feature by placing the NTC jumper (JP5) in
the lower position. The charger is now set to charge
at 1A and use minimum charge current (IDET =
100mA) for charge termination.
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 (the undervoltage lockout threshold), the
CHRG LED will turn on and the preconditioning
trickle charge of 100mA will begin flowing. Adjust
the battery simulator power supply to 3V. At ap-
proximately 2.9V, the charge current will abruptly
increase 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 4.375V, 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
selected (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).
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 788B
SINGLE CELL LI-ION BATTERY CHARGER WITH NTC
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 ter-
minal.
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.
For batteries that have an internal thermistor to
sense battery temperature, place the NTC jumper
(JP5) in the EXT (upper) position and connect the
thermistor wire to the NTC terminal on the PC
board. Note, R6 must be the same value as the
thermistor at 25°C.
See LTC4061-4.4 Data Sheet for additional
information.
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 788B
SINGLE CELL LI-ION BATTERY CHARGER WITH NTC
Figure 1. Demo Circuit Hookup and Jumper Information
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