Ideal for single- and dual-cell Li-Ion packs with coke or graphite anodes? Dropout voltage as low as 0. Optional temperature-monitoring before and during charge? Integrated voltage and current regulation with programmable charge-current and high- or low-side current sensing? Integrated cell conditioning for reviving deeply discharged cells and minimizing heat dissipation during initial stage of charge?
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MAY ? They combine high-accuracy current and voltage regulation, battery conditioning, temperature monitoring, charge termination, charge-status indication, and AutoComp charge-rate compensation in a single 8-pin IC.
The bq continuously measures battery temperature using an external thermistor. For safety, the bq inhibits charge until the battery temperature is within user-defined thresholds. The bq then charges the battery in three phases: conditioning, constant current, and constant voltage. If the battery voltage is below the low-voltage threshold, V min , the bq precharges using a low current to condition the battery.
The conditioning current also minimizes heat dissipation in the external passelement during the initial stage of the charge. After conditioning, the bq applies a constant current to the battery. An external sense-resistor sets the current. The sense-resistor can be on either the high or low side of the battery without additional components. The constant-current phase continues until the battery reaches the charge-regulation voltage.
AutoComp is a trademark of Texas Instruments. Products conform to specifications per the terms of Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters. For single and dual cells, the bq is offered in four fixed-voltage versions: 4.
The bq automatically restarts the charge if the battery voltage falls below the V RCH threshold. The designer also may use the AutoComp feature to reduce charging time. This proprietary technique allows safe and dynamic compensation for the internal impedance of the battery pack during charge.
Note the difference in pinout for this package. The external resistor can be placed on either the high or low side of the battery. See schematics for details. The voltage-regulation output may be programmed to vary as a function of the charge current delivered to the battery. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability. For high-side current sensing configuration 2.
Figure 1 shows the schematic of charger using a PNP pass transistor. Figure 2 is an operational state diagram, and Figure 3 is a typical charge profile. Operation Flowchart 8 www. Typical Charge Profile qualification and precharge When power is applied, the bq starts a charge-cycle if a battery is already present or when a battery is inserted.
Charge qualification is based on battery temperature and voltage. The bq suspends charge if the battery temperature is outside the V TS1 to V TS2 range and suspends charge until the battery temperature is within the allowed range.
The bq also checks the battery voltage. If the battery voltage is below the precharge threshold V min , the bq uses precharge to condition the battery. The conditioning current also minimizes heat dissipation in the external pass-element during the initial stage of charge.
See Figure 3 for a typical charge-profile. F PACK? The bq monitors charge current at the SNS input by the voltage drop across a sense-resistor, RSNS, in series with the battery pack. High-Side Current Sensing Figure 6. This input is tied directly to the positive side of the battery pack. The bq is offered in four fixed-voltage versions: 4.
Other regulation voltages can be achieved by adding a voltage divider between the positive and negative terminals of the battery pack and using bqT or bqW. The voltage divider presents scaled battery-pack voltage to BAT input. See Figure 7 and Figure 8.
Optional Voltage Divider for Nonstandard Regulation Voltage, Low-Side Current Sensing charge termination and recharge The bq monitors the charging current during the voltage-regulation phase.
The bq declares a done condition and terminates charge when the current tapers off to the charge termination threshold, I TERM. A new charge cycle begins when the battery voltage falls below the V RCH threshold.
A negative- or a positive-temperature coefficient thermistor NTC, PTC and an external voltage divider typically develop this voltage. See Figure 9.
See Figure Where R TC is the cold temperature resistance and R TH is the hot temperature resistance of thermistor, as specified by the thermistor manufacturer. RT1 or RT2 can be omitted If only one temperature hot or cold setting is required.
RT2 BAT? The following table summarized the operation of the STAT pin. When interfacing the bq to a processor, the user can use an output port, as shown in Figure 11, to recognize the high-Z state of the STAT pin. In this configuration, the user needs to read the input pin, toggle the output port and read the STAT pin again.
In a high-Z condition, the input port always matches the signal level on the output port. This feature prevents draining the battery pack during the absence of VCC.
The device should be chosen to handle the required power dissipation, given the circuit parameters, PCB layout and heat sink configuration.
Determine the maximum power dissipation, PD, in the transistor. The worst case power dissipation happens when the cell voltage, V BAT , is at its lowest typically 3 V at the beginning of current regulation phase and VI is at its maximum. Where VCS is the voltage drop across the current sense resistor. Select a collector-emitter voltage, V CE , rating greater than the maximum input voltage.
A V device will be adequate in this example. NOTE: The beta of a transistor drops off by a factor of 3 over temperature and also drops off with load. Therefore, note the beta of device at I REG and the minimum ambient temperature when choosing the device.
This beta should be larger than the minimum required beta. Ion bqC. See Figure 4. Where VD is the forward voltage drop across the reverse-blocking diode if one is used , and VCS is the voltage drop across the current sense resistor.
Select a drain-source voltage, V DS , rating greater than the maximum input voltage. A 12 V device will be adequate in this example. Verify that the available drive is large enough to supply the desired charge current. The bq works with both regulated and unregulated external dc supplies. If a non-regulated supply is chosen, the supply unit should have enough capacitance to hold up the supply voltage to the minimum required input voltage at maximum load.
If not, more capacitance must be added to the input of the charger. The user can add output capacitance in order to control the output voltage when a battery is not present. The charger quickly charges the output capacitor to the regulation voltage, but the output voltage decays slowly, because of the low leakage current on the BAT pin, down to the recharge threshold. Addition of a 0. F ceramic capacitor, for instance, results in a mV pp ripple waveform, with an approximate frequency of 25Hz.
Higher capacitor values can be used if a lower frequency is desired. The COMP pin must not be left floating. Figure 12 outlines the major components of a single-cell Li-Ion battery pack. The Li-Ion battery pack consists of a cell, protection circuit, fuse, connector, current sense-resistors, and some wiring. Each of these components contains some resistance.
Total impedance of the battery pack is the sum of the minimum resistances of all battery-pack components. Using the minimum resistance values reduces the odds for overcompensating. Overcompensating may activate the safety circuit of the battery pack. V PACK is the voltage across the battery pack. AutoComp Circuits 18 www. All linear dimensions are in millimeters. This drawing is subject to change without notice. Body dimensions do not include mold flash or protrusion.
Pin SN 0. A - Dimension Millimeters Max. Controlling dimension: millimeters. Inches shown for reference only. Leads shall be coplanar within 0,08 mm at the seating plane. Dimension applies to the flat section of the lead between 0,10 mm and 0,25 mm from the lead tip. NRND: Not recommended for new designs.
Device is in production to support existing customers, but TI does not recommend using this part in a new design.
Brief analysis of lithium battery linear charge management chip BQ2057 and its application
The package is shown in Figure Its model is shown in Table When the working voltage is too low, the charger enters the sleep mode. If the working voltage is normal, check whether the battery temperature is within the set range. If not, enter the temperature. Fault mode, otherwise the battery voltage VBAT is detected.