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2021-07-11
Portable power applications are broad and diverse. Products range from wireless sensor nodes with average power consumption of only a few μW to vehicle-mounted medical or data acquisition systems with hundreds of watt-hour battery packs. However, despite their wide variety, they have shown a relatively consistent trend. Designers are constantly asking their products to have higher power to support more functions and expect to be able to charge the battery from any available power source. . The first trend requires an increase in battery capacity. Unfortunately, users often lack patience and the increased battery capacity must be charged within a reasonable amount of time, which inevitably leads to an increase in charging current. The second trend requires great flexibility in battery charging solutions. We will explore these issues one by one in more detail.
Higher power
New handheld devices (whether consumer or industrial) may include a cellular modem, a WiFi module, a Bluetooth module, a large backlit display, and more. The power architecture of many handheld devices can be reflected through cellular phones. Typically, a 3.7V lithium ion battery is used as the primary power source due to its high weight (Wh/kg) and volume (Wh/m3) energy density. In the past, many high-power density devices used a 7.4V lithium-ion battery to reduce current demand, but the availability of inexpensive 5V power management ICs has led to more and more handheld devices switching to lower voltage architectures. Tablets do a good job of this. Standard Tablets have a wealth of features and a very large (for portable devices) screen. When powered by a 3.7V battery, the battery must have a capacity of several thousand mAh. In order to be able to charge such a battery within a few hours, a charging current of several thousand mA is required.
However, consumers also want to be able to charge their high-power devices from a USB port when no high-current wall adapters are available, a desire not to be contained because of the high charging current described above. To meet these requirements, the battery charger must be able to charge at high current (>2A) when the wall adapter is available, but still efficiently utilize the 2.5W to 4.5W power provided by the USB port. In addition, the product must avoid sensitive downstream low-voltage components from overvoltages that could cause damage, seamlessly directing high currents from a USB input, a wall adapter or battery to the load, and minimizing power loss. At the same time, ICs must safely manage battery charging algorithms and monitor critical system parameters.
Solve the power problem of single-cell battery-powered portable products
Although not seem to find a single IC to meet the above requirements, but may wish to consider the LTC4155, which is a high power, I2C control, high efficiency PowerPathTM manager, ideal diode controller and a lithium ion battery charger. Designed to efficiently deliver up to 3A from a wide range of 5V supplies, the device delivers more than 3.5A for battery charging and system use. Even at these high current levels, the 88% to 94% efficiency of the LTC4155 can relax thermal budget constraints. The LTC4155's Switching PowerPath topology seamlessly manages power delivery from two input power sources (such as wall adapters and USB ports) to the device's rechargeable Li-Ion battery, and prioritizes system load when input power is limited powered by.
The LTC4155's switching regulator acts as a transformer, allowing the load current on VOUT to exceed the current drawn by the input supply, greatly improving the efficiency of battery charging available compared to conventional linear mode chargers. As shown in the previous example, the LTC4155 can charge up to 3.5A with high current, which reduces charging time. Unlike conventional switch battery chargers, the LTC4155 has an “on-the-fly” capability to ensure immediate system power when plugged in, even if a failed battery or a deeply discharged battery is used.
It is important to monitor the safety of the battery when charging the battery at high speed. The LTC4155 will automatically stop charging when the battery temperature drops below 0°C or rises above 40°C (measured by an external negative temperature coefficient [NTC] thermistor). In addition to this autonomous feature, the LTC4155 provides a 7-bit extended scale analog-to-digital converter (ADC) for monitoring battery temperature at approximately 1°C resolution. Combined with four available floating voltage settings and 15 battery charge current settings, the ADC can be used to create a battery-based custom charging algorithm.
The NTC ADC results are obtained from a simple 2-wire I2C port, which adjusts the charge current and voltage settings accordingly. The I2C port also provides compatibility with the USB specification by controlling 16 input current limit settings, including those compatible with USB 2.0 and 3.0 specifications. The communication bus allows the LTC4155 to provide additional status indication information such as input power status, charger status, and fault status. USB OTG (On-The-Go) support provides a 5V power supply back to the USB port without any additional components.
The LTC4155's dual-input, priority multiplexer selects the most appropriate input (wall adapter or USB) based on a user-defined priority (the adapter input is the default preference). An overvoltage protection (OVP) circuit is used to protect both inputs from damage caused by accidental application of high voltage or reverse voltage. The LTC4155's ideal diode controller ensures that enough power is always available to VOUT, even if the input power is insufficient or missing.
For many portable applications such as tablets or industrial barcode scanners, managing two inputs (eg USB and wall adapters) is sufficient. However, designers of portable devices continue to explore ways to charge batteries from any available power source.
Multiple input power supplies
There are many reasons why users want to charge the battery from a variety of input sources. Some applications may need to leave the grid and expect to be powered by solar panels . Other applications want to have the convenience of charging from wall adapters, car batteries or high voltage industrial or telecom power supplies. Whatever the reason, this requirement puts a heavy burden on the battery charging system. Most battery chargers use a buck (switch or linear) architecture to charge the battery from a voltage source that is higher than the maximum battery voltage. Earlier charger products were typically limited to an input voltage of approximately 30V. Such limitations have prevented designers from considering telecommunications power as a viable input source or solar panels with a 42V open circuit voltage. In some cases, it is expected that the voltage range of the input supply will rise above the battery voltage and below the battery voltage. Solutions designed to address these challenges often require the integration of high-precision current-sense amplifiers, ADCs, microprocessors for controlling charging operations, high-performance DC/DC converters, and ideal diodes or multiplexers. Linear Technology has introduced a superior solution.
Powerful and unmatched flexibility charging solution
The LTC4000 converts any externally compensated DC/DC power supply into a full-featured battery charger with PowerPathTM control. Common DC/DC converter topologies that the LTC4000 can drive include, but are not limited to, buck, boost, buck-boost, SEPIC, and flyback. The device provides precise input current and charge current regulation and operates over a wide input and output voltage range of 3V to 60V, making it compatible with a wide range of input voltage sources, battery pack sizes, and chemistries. Due to its versatile configuration, the device is typically used in a wide range of applications, including high-power battery charger systems, high-performance portable instruments, battery backup systems, battery-equipped industrial equipment, and notebook/small notebooks.
In addition to supporting a variety of different DC/DC topologies, the LTC4000's high voltage capability enables it to utilize virtually any input supply to form a powerful battery charging solution. To ensure that power from these inputs can be delivered to the appropriate load, the LTC4000 employs an intelligent PowerPathTM topology that prioritizes power to the system load when input power is limited. The LTC4000 provides low-loss reverse current protection, low-loss charging and discharging of the battery, and “instant-on” operation by controlling the external PFET to ensure immediate system power when plugged in, even if a failed Batteries or batteries that are deeply discharged are no exception. An external sense resistor provides input current and battery charge current information, allowing the LTC4000 to be used with converters ranging from a few milliwatts to several kilowatts.
The LTC4000's full-featured battery charge controller charges a wide range of battery chemistries, including lithium-ion/lithium polymer/lithium iron phosphate batteries, sealed lead-acid batteries (SLA), and nickel batteries. In addition, the battery charger features high-precision current sensing to provide a low detection voltage for high current applications.
in conclusion
Designers of new portable products are engaged in challenging work, especially when faced with power. Customers are constantly chasing features that require more power, so larger batteries are required. At the same time, customers also want the convenience of charging these batteries from almost all available power sources. While the above trends in portable power supplies have created design challenges, the LTC4155 and LTC4000 have greatly simplified the design effort. In low-voltage systems, the LTC4155 efficiently delivers up to 3.5A of charge current with many high-performance features. The LTC4000 is capable of delivering a powerful charging solution with virtually any input with unparalleled performance and flexibility.
