A number of ultra-thin portable applications on the market today use single-cell Li-Ion/Polymer batteries, which require a full-featured, reliable battery charger that provides excellent functionality, very small size, and a very good price/performance ratio. And flexibility. The AAT3681A meets all of the above requirements and requires only one external component.
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The AAT3681A's very small package size is only 2.0 x 2.1mm, making it ideal for portable and ultra-portable applications. This device is the ideal device for plug-and-play charger designers, helping designers save on design and PCB layout time, as well as helping to bring products to market quickly.
AnalogicTech offers a wide range of power conversion solutions designed for portable and handheld battery-powered applications. One of the most important features of a successful design is that the match between the device and the target application is perfect.
As far as the AAT3681A is concerned, the capabilities of modern portable applications are expanding at an alarming rate, and all new types of functionality are being added to meet market requirements. Therefore, the purpose of providing this device is to integrate all the functions required for a single-cell Li-Ion battery charger and to minimize the design effort of the circuit designer. Now they can focus more on the main goal of charger design than on the in-depth details of battery charger design.
The AAT3681A Battery Manager is a highly integrated single-cell Li-Ion/Polymer battery charger IC designed to charge from a DC power supply or USB port with input voltages up to 7.5V. It requires only one external component to perform all functions. The AAT3681A accurately regulates battery charging voltage and current for a 4.2V (or 4.375V) Li-Ion/Polymer battery.
When charging from an AC adapter or USB port, battery charging currents up to 300mA can be set with an external resistor. The state of charge of the battery is continuously monitored and the device automatically shuts down in the event of an error condition such as an overvoltage, short circuit or overheating, thereby protecting the charging device, the control system and the battery in a charged state. The AAT3681A provides a status monitoring output pin that indicates the state of charge of the battery by directly driving an external LED.
The AAT3681A is available in a space-saving 8-pin lead-free, heat-resistant SC70JW package with a footprint of only 2.0 x 2.1mm and an operating temperature range of -40°C to +85°C.
The recently released AAT3681A is a single-cell battery charger that is suitable for many applications, including: 1) Bluetooth headset; 2) DECT headset; 3) digital camera; 4) MP3 portable music player, PMP; 5) wristwatch; 6) Other lithium ion/polymer battery powered equipment.
Although the device is designed to make the charger design very fast, simple, and easy, it integrates many features to help optimize battery charging performance and PCB layout area. The following are some of these features and functions: 1) USB or AC adapter system battery charger; 2) 15mA to 300mA programmable charge current; 3) 4.0V to 7.5V input voltage range; 4) with internal charging device Highly integrated; 5) reverse blocking diode; 6) automatic current sensing; 7) automatic recharge sequencing; 8) fully charged automatic shutdown / sleep mode / charge termination; 9) shutdown current less than 1uA; 10) battery precharge Automatic trickle charge under overvoltage and emergency overheat protection; 11) Power-on reset and soft-start; 12) LED status pin; 13) 8-pin 2.0×2.1mm SC70JW package.
Module description
Single-cell Li-Ion/Polymer batteries are becoming the primary choice for portable and ultra-portable applications. Developed for this end market, the AAT3681A is a high-performance battery charger designed to charge a single-cell Li-Ion/Polymer battery from an external power source at currents up to 300mA. This charging current can be customized from a wide range of 15mA to 300mA with an external resistor. This allows the adapter/USB port to perform fast charging in different applications. It is a stand-alone charging solution that requires only one external component to perform all functions. This device accurately regulates battery charging voltage and current for a 4.2V Li-Ion/Polymer battery pack
The device is specified for operation over the -40°C to +85°C temperature range. At a given constant current charge level, when the operating ambient temperature exceeds the power dissipation capability of the device package, its charge control will enter a thermal limit state.
The device provides a status monitor output pin that directly drives an external LED to indicate battery charge status. The device junction temperature and state of charge are adequately monitored to prevent false conditions.
The AAT3681A implements a complete protection system. When an overvoltage or overtemperature error condition occurs, the device will automatically shut down to protect the charging device, control system, and battery under charge.
Charging operation
The AAT3681A has four basic charging modes for the entire battery charge cycle: precharge / trickle charge, constant current / fast charge, constant voltage charge and charge termination.
Battery precharge
Before the start of charging, the AAT3681A checks several conditions to ensure a safe charging environment. The input power must exceed the minimum operating voltage or undervoltage lockout threshold to initiate the charging sequence. When these conditions are met and the battery is connected to the BAT pin, the AAT3681A checks the battery status. If the battery voltage is below the pre-charge threshold, the charge control circuit begins pre-charging the battery. The battery precharged trickle charge current is one-tenth of the fast charge constant current.
For example, if the programmable fast charge current is 300mA, the precharge current is 30mA. Battery cell precharge is a safety precaution for deep discharge cells, which also helps limit power dissipation on the turn-on transistor because the voltage difference across the device is maximized. The constant current rechargeable battery unit is precharged until the voltage on the BAT pin exceeds the precharge voltage threshold. After reaching this point, the device begins the constant current charging phase. The constant current charging amplitude is programmed by the user by setting the resistor. The AAT3681A maintains a constant current charging mode until the battery reaches the voltage regulation point.
Constant voltage charging
During the constant current fast charging phase, when the battery voltage reaches the output charge regulation threshold, the system enters the constant voltage charging mode. The regulated voltage level is set to 4.2V (±0.5%) at the factory. The charging current in constant voltage mode drops because the battery unit in charge reaches its maximum capacity quickly.
Charge cycle termination and recharge sequence
In constant voltage mode, when the charging current drops to 10% of the fast charging current, the device terminates charging and goes to sleep. The charger will remain asleep until the battery voltage drops below the battery recharge threshold.
Due to the very low current consumption during sleep, the AAT3681A minimizes battery leakage when not charging. This feature is especially useful for applications where the input power level may be lower than the charge battery level or undervoltage lockout level. In these cases, when the AAT3681A input voltage drops, the device goes to sleep and automatically resumes charging once the input power source recovers from an error condition.
Thermal considerations
The AAT3681A is available in an SC70JW-8 package that dissipates up to 687mW of power and has a thermal resistance of up to 160°C/W when properly mounted on a PCB. There are a number of factors that should be considered when designing the PCB and arranging the location of the charger IC with other heat sink components in a particular application design.
The ambient temperature of the charger IC will also have an impact on the thermal limits of the battery charging application. The maximum limit that can be expected under a particular environmental condition can be estimated by the following discussion.
First, the maximum power consumption in a particular environment can be calculated by:
among them:
PD(MAX) = maximum power consumption (W)
θJA = package thermal resistance (°C/W)
TJ(MAX) = maximum device junction temperature (°C) [135°C]
TA = ambient temperature (°C)
Second, the power consumption can be calculated by:
among them:
PD = total power consumption of the device
VIN = input voltage
VBAT = battery voltage on the BAT pin
ICH = constant charging current programmed for an application
IOP = quiescent current consumed by the charger IC under normal operating conditions [0.5mA]
By way of substitution, we can deduce the maximum charging current before reaching the thermal limit condition (thermal cycle). This maximum charging current is a key factor in designing battery charger applications.
In summary, the worst case scenario is the maximum voltage drop across the charger IC, at which point the battery voltage is charged to the precharge voltage threshold.
Protection circuit; overvoltage protection
An overvoltage event is defined as the voltage on the BAT pin exceeds the maximum battery charging voltage and is set at the overvoltage protection threshold. If an overvoltage event occurs, the AAT3681A charge control circuit will shut down the device until the voltage on the BAT pin falls below the OVP voltage level. The AAT3681A resumes normal charging operation after the overvoltage condition is removed.
Protection circuit; thermal shutdown
The AAT3681A has a thermal protection control circuit that turns off the charging function once the internal die temperature exceeds the preset thermal limit threshold. Once the internal die temperature falls below the thermal limit, it automatically returns to the previous normal state of charge.
Programmability of charging current
The user can program the constant current charge level with a set resistor placed between the ISET pin and ground. Fast charge accuracy and precharged trickle charge current are determined by the tolerance of the set resistor used. Therefore, a metal film resistor with a 1% tolerance is recommended. The fast charge constant current ranges from 15mA to 300mA.
in conclusion
The AAT3681A provides all the functions of a battery charger in a plug-and-play manner. It requires only one external component to perform all operations. This device offers a great price/performance ratio. A small footprint of 2mm x 2.1mm saves PCB space. The device is suitable for a wide range of applications, from Bluetooth headsets to MP3 players to watches. The AAT3681A is the newest member of AnalogicTech's family of different complexity and category products.
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