LINEAR TECHNOLOGY LTC4062 Single Cell Li-Ion Battery Charger With Comparator User Guide
- June 6, 2024
- LINEAR TECHNOLOGY
Table of Contents
LINEAR TECHNOLOGY LTC4062 Single Cell Li-Ion Battery Charger With
Comparator
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 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. 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%
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
(DETECT). 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 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| Idetect 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 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
(I DETECT) is used, the charge cycle ends when the Charge current drops below
the DETECT 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 program-ming
resistor from the CURRENT MONITOR terminal to the ground.
The COMP IN terminal is connected to the comparator’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 the jumper (JP5) is in the BAT
(lower) position. See datasheet 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 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 the evaluation by moving the jumpers to the following 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) 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
- An ammeter 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 terminals to measure the
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 programmed
current) will begin flowing. The COMP LED will be off because the battery
voltage is below 2.910V. 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 4.200V, 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 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). Reducing the battery simulator down to approx. 2.910V will result in the comparator changing states (LED off). The micropower comparator receives power from the battery allowing the comparator to be active when input power is removed. 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.
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 to charge current).
Likewise, another minimum charge current termination level 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. See LTC4062 Data Sheet
for additional information.
Figure 1. Demo Circuit Hookup and Jumper Information