LINEAR TECHNOLOGY LTC4061-4.4 Single Cell Li-Ion Battery Charger with Ntc User Guide
- June 3, 2024
- LINEAR TECHNOLOGY
Table of Contents
TECHNOLOGY LTC4061-4.4 Single Cell Li-Ion Battery Charger with Ntc
User Guide
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 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 conditions 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. Terminals are pro- 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 (DETECT). 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
Table 1. Typical Specifications (25°C)
Input Voltage Range VIN| 4.5 to 8V (upper range limited by PC board power
dissipation)
---|---
Input Undervoltage Lockout| 3.8V
Output Float Voltage VBAT (constant voltage mode)| 4.375V ±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%
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 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 current 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 onboard
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| (detect Current| Charge Current|
Idetect Current
HIGH| C| 1A| 100mA| 500mA| 50mA
C / 5| 200mA| 100mA| 100mA| 50mA
LOW| C| 500mA| 100mA| 250mA| 25mA
C/5| 100mA| 100mA| 50mA| 25mA
The CHRG LED always indicates the presence of a charge current that is greater
than the DETECT current level that is selected by the IDET jumper (JP4). The
LED is on for a 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 the 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 programming resistor from the current monitor terminal to the ground. See the data sheet for details.
QUICK START PROCEDURE
The charger can be evaluated using an actual Lithium 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 provide 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 simulator, 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’s 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 the 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) 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 uses 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
- An ammeter or 100mΩ 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 terminals to measure the
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 approximately 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 accepting a 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 current 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 voltage 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).
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 removing Jumper JP3 and adding a
suitable external resistor from the Current Monitor terminal to the ground
(Note that the position of JP2 and JP4 will also determine the charge
current).
Likewise, other minimum charge current termination 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 termination 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 dependent on the value of the output
capacitor. With a 2.2µF output capacitor, the frequency is approximately 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 voltages caused by the capacitor when the input voltage 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.
Figure 1. Demo Circuit Hookup and Jumper Information
See the table on the lower section of the demo board for all pre-programmed
charge and termination current levels.
Note: This demonstration circuit must be used with Batteries designed to be
charged at the higher voltage of 4.375V
| IDET= 100mA| IDET= C/10
---|---|---
ICHG-1| ICHG-2| | CHARGE CURRENT| IDET
100mA| CHARGE CURRENT| IDET
C/10
HIGH| C| | 1A| 100mA| 500mA| 50mA
C/5| 200mA| 100mA| 100mA| 50mA
LOW| C| 500mA| 100mA| 250mA| 25mA
C/5| 100mA| 100mA| 50mA| 25mA
NOTES: UNLESS OTHERWISE SPECIFIED
- ALL RESISTORS ARE IN OHMS, 0402. ALL CAPACITOR ARE 0402.
- INSTALL SHUNTS ON JP1-JP5 PIN 1 AND 2.
CUSTOMER NOTICE
LINEAR TECHNOLOGY HAS MADE ITS BEST EFFORT TO DESIGN A CIRCUIT THAT MEETS
CUSTOMER•SUPPLIED SPECIFICATIONS, HOWEVER, IT REMAINS THE CUSTOMER’S
RESPONSIBILITY TO VERIFY PROPER AND RELIABLE OPERATION IN THE ACTUAL
APPLICATION. COMPONENT SUBSTITUTION AND PRINTED CIRCUIT BOARD LAYOUT MAY
SIGNIFICANTLY AFFECT CIRCUIT PERFORMANCE OR RELIABILITY. CONTACT LINEAR
TECHNOLOGY APPLICATIONS ENGINEERING FOR ASSISTANCE.| CONTRACT NO.| 1630
McCarthy Milpitas. CA 95035Blvd.
Phone: (408)432-1900
Fax: (408)434-0507
LTC Confidential-For Customer Use Only
---|---|---
APPROVALS
KIM T.
CHECKED:| TITLE: SCHEMATIC
SINGLE-CELL LI-ION BATTERY CHARGER WITH NTC
APPROVED:
ENGINEER: FRAN H.
SIZE
A| DWG NO,
DC788B * LTC4061EDD-4.4| REV
A
DESIGNER:
THIS CIRCUIT IS PROPRIETARY TO LINEAR TECHNOLOGY AND SUPPLIED FOR USE WITH
LINEAR TECHNOLOGY PARTS.|
DATE: Thursday, December 16, 2004| SHEET 1 OF 1
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