With the wide application of portable electronic products in various fields, the performance requirements of rechargeable batteries such as cadmium cadmium batteries, nickel hydride batteries and lithium batteries as power sources are getting higher and higher, and the development of charger integrated circuits with them is increasingly attracting attention. .
In order to occupy this market, semiconductor device manufacturers all over the world have launched their own new charger IC products. There are many manufacturers, new products are developing fast, and competition is fierce, reaching an unprecedented level. According to incomplete statistics, there are more than a dozen manufacturers of charger integrated circuits, and the product models are shown in the following table.
Charger performance indicators
The main requirements of modern chargers are short charging times and safety (without damaging the battery and shortening battery life). This requires the charger IC to drive large currents with strong detection capability and a complete charging process.
Generally, the charging time of the fast charger is within 1 hour, so the charging current is required to be large. Most charger ICs allow a charging rate of 1c-5c (the old charger is charged in the standard way, and its charging rate is C/10). For example, PHILIPS' TEA1101 has a charging rate of 1c-5c. It can charge up to 800mAh of battery in 0.5 hours and charge 1600mAh of battery in 1 hour. ICS's 1CS1700 uses a 4C charging rate and can be filled with 500mAh of cadmium-cadmium batteries in 20 minutes. BENCHMARQ uses a bq2005 integrated circuit charger to charge nickel-metal hydride batteries for 1 to 1.5 hours, while nickel-cadmium-filled batteries only take 10 to 20 minutes.
During the charging process, the internal temperature and pressure of the battery increase with the increase of the voltage, especially when it is rapidly filled, the speed of increase is very fast. The relationship curve is shown in the figure below.
Whether the battery is full or not is based on one or more of the following: (1) A ΔV/Δt (generally referred to as a △) is detected; (2) A set maximum charging voltage Vmax is detected (according to the number of rechargeable batteries) And (3) the highest detected temperature Tmax, AT or ΔT/Δt; (4) reaches the set charging time tmax.
The detection of -A is the main basis for most charger ICs to judge whether they are full, and Vmax, Tmax, and tmax are generally only used as protection measures, because when charging, the measurement temperature and the ambient temperature have a large influence, and it is not easy to measure.
For NiMH batteries, the high temperature caused by overcharging exacerbates internal hydrogen activity, and the pressure increases too high and there is a danger of explosion. In addition, when the nickel-hydrogen battery is fully charged, its Δ value is small, even ΔV/Δt≈O, so the detection sensitivity is very high. Therefore, some charger integrated circuits are considered to be full when detecting the AV/At=O of the nickel-hydrogen battery, and there are also chargers for detecting AT/At as the basis for ending the fast charging of the nickel-hydrogen battery (bq2003). For example, PHA. IPS's TEA1100 has a detection resolution of 7.5 mV/cell, and the resolution of TEA1101 developed thereafter is increased to 2 mV/cell. The latter is suitable for charging nickel-metal hydride batteries.
Charging method is the same
The old-fashioned charger uses constant voltage charging or constant current charging, that is, the charging voltage and current are constant throughout the charging process. The new generation of charger ICs varies in design process due to different designers.
Generally, the charging process of the simplest fast charger is divided into two phases: fast charging and trickle charging. When the charger detects a â–³, it automatically switches from fast charging to trickle charging. The fast charging rate and the slip current charging rate can be selected by the user. For example, the rapid charging rate of TEA1101 is 1c~5c, and the trickle charge rate can be selected from 0.05c to 0.25C.
ICS's ICS1700 uses the company's patented charging method (Reflex charging method). In the charging process, it is in seconds and is divided into four stages in each unit. The first stage is 983ms, in the state of charge; the second stage is 2ms, stop charging; the third stage is 5ms, large current discharge; the fourth stage is lOms, for detecting and reading voltage data. This charging method is shown in Figure (a). This charging method prevents chemical crystallization from forming on the electrode plates during charging.
The ICS1700 has a 16-bit ROM inside and a simple digital signal processor (DSP). The ICS1700A has new improvements, adding a soft-start function that is still charged in four stages, as shown in Figure (b).
As shown above, BENCHMARQ's bq2003 charging is divided into four stages, 1 to be charged (for battery detection); 2 for discharge (each battery is placed at 1V); 3 for fast charging (pulse charging); 4 for supplementary charging (allow The cycle of stopping for 30 seconds after 4 seconds is also charged by pulse.
ChipSGARDEN's UT500 has a similar charging method to the ICS1700. It has a high current discharge time of 4ms, as shown in the figure below.
The ATC105 charger IC uses a method of first discharging and recharging, and has an automatic conversion function. This type of charging prevents the "memory effect" (or memory effect) caused by charging the battery when it is not used up.
Additional features have their own
In order to improve the performance of the charger, companies have added some additional features that are easy to use on the charger IC. For example, in addition to using an LED to display the charging status, the ICS1700 also uses two LEDs to indicate whether there is over temperature and whether the battery is defective. In addition to using two LEDs to display the charging and discharging states, the ATC105 also has a buzzer that can sound an alarm to indicate battery failure (battery open circuit, short circuit, etc.), as shown in the table below. CHIPSGARDEN's UT500 has five LEDs that represent the percentage of charging voltage (20%, 40%, 60%, 80%, 100%).
If 100% of the LEDs are on, it means the battery is sufficient, as shown in the figure above. It can also drive LEDs through the decoder to make it more visible, as shown in the following figure.
Reduce pin simplification circuit
The number of integrated circuit pins reflects the complexity of the internal structure and, to a certain extent, reflects the demand for external components. That is to say, under the condition that the charger performance is satisfied, the charger integrated circuit has fewer pins, and the design level is higher.
In BENCHMARQ's charger IC, the bq2001 is a 24-pin device. Bq2003 is a 16-pin device, and the latest bq2002 is an 8-pin device. bq2002 can also charge nickel-cadmium batteries and nickel-hydrogen batteries, which can detect a â–³, the highest temperature Tmax and the longest charging time tmax. It can be charged in three stages (fast charge, supplementary charge and trickle charge). The advent of the 8-foot bq2002 is a big breakthrough.
DALLAS's DS1633 charger IC is not as functional as other companies' products. It only detects the Vmax and charging time tmax of the rechargeable battery, but it is a three-terminal device that does not require external components and is very convenient to use. This is its unique advantage. The DS1633 has an internal EPROM with a charging time of 8 hours. The charging current varies depending on the model, as shown in Table 3.
Novel plug charger integrated circuit
BURR-BROWN (BB)'s DC-151 is the latest in ultra-small, full-featured plug-in products. It has two charger integrated circuits, BCC100 and BC101. The characteristics of this charger are: (1) small volume (53crri3), light weight (100g), (2) rechargeable nickel-cadmium battery and nickel-hydrogen battery; (3) a â–³ detection function; (4) fast charging current It is 600mA. The trickle charge current is 60mA (filling 5 batteries); (5) there is a tmax controller inside; (6) the input is connected to the AC mains input and
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