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ISL6292BCRZ Datasheet(PDF) 7 Page - Intersil Corporation |
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ISL6292BCRZ Datasheet(HTML) 7 Page - Intersil Corporation |
7 / 12 page 7 FN9139 .1 April 19, 2005 Theory of Operation The ISL6292B is based on the Intersil Patent-pending dual-mode charging technology. The dual-mode technology generates very low heat, which enables the charger to be used in space-limited applications. To take advantage of the low-heat feature, a current-limited ac/dc converter is required as the power supply to the charger. The current-limited supply has the I-V characteristics shown in Figure 1. The supply is a dc source before the load current reaches the limited current ILIM. Once the current limit is reached, the supply current cannot increase further; instead, the supply voltage falls. The current-limited supply is equivalent to a voltage source with an equivalent output impedance or a current source, depending on the region it operates at, as shown in Figure 1. The ISL6292B charges a battery with the traditional constant current/constant voltage (CC/CV) profile. The constant current is determined by the current limit ILIM of the supply during the constant-current charge mode. To ensure dual- mode operation, the current protection level set by the IREF pin should be higher than ILIM. In the constant-voltage charge mode, the battery voltage is regulated at 4.2V. When the battery voltage is below the VMIN given in the Electrical Specification, the charger preconditions the battery using trickle charge mode. The trickle-charge current is 10% of the protection current level programmed by the IREF pin. Figure 2 shows the typical waveforms in a charge cycle of the dual mode operation. When the battery is below VMIN, the charge current is 10% of IREF set by the IREF pin. Since the charge current is much less than the ILIM, the ac/dc converter operates in the voltage source region. Once the battery voltage exceeds VMIN, the charger starts to fully turn on the internal P-channel power MOSFET. The ac/dc converter operates in the current-limited region and its voltage is pulled down to a level slightly higher than the battery voltage. As shown in Figure 2, the charge current is ILIM and is lower than IREF. As the battery voltage reaches the 4.2V VCH, the charge current starts to decrease. The ac/dc supply moves out of the current-limit region and becomes a voltage source again. When the charge current reaches a programmable end-of-charge (EOC) level set by the IMIN pin, the charger sends out an EOC indication. The real termination of the charger happens at the end of a total charge time set by the TIME pin. The power dissipation is also shown in Figure 2. The power dissipation in both the trickle mode and the constant-current (CC) mode are very low. The possible peak power occurs at the transition from the CC mode to the constant-voltage (CV) mode. This peak power is much lower than the peak power normally seen in a linear charger and can be further reduced by properly designing the ac/dc converter. One simple approach is to design the ac/dc converter output voltage just high enough to fully charge the battery (normally lower than 5V). More information can be found in the ISL6292 datasheet available at http://www.intersil.com. To ensure the thermal safety, the ISL6292B has an internal thermal fold- back function that automatically reduces the charge current if the internal temperature typically rises above 100°C. The ISL6292B offers many other features. The trickle current, the CC charge current, and the end-of-charge (EOC) current are all programmable. A thermal foldback function monitors the internal temperature and reduces the charge current when the internal temperature rises above 100°C to prevent further temperature rise. A safety timer sets the charge time limit for both trickle mode and fast mode charge. When the battery voltage drops after the charge cycle terminates, the charger automatically starts recharging the battery to full. Two indication pins are designed to drive a tri-color LED (a red and a green LED in the same package). A simple thermistor circuit interface allows the user to set a different level of ambient temperature before and after the charger starts. All these features are described in detail in the Application Information section. FIGURE 1. THE I-V CHARACTERISTICS OF THE CURRENT- LIMITED AC/DC CONVERTER. V NL V FL I LIM r O V NL I LIM r O = (V NL - VFL )/ILIM A B C FIGURE 2. TYPICAL CHARGE CURVES USING A CURRENT- LIMITED ADAPTER. V CH V MIN V IN I REF I REF/10 P 1 P 2 I LIM Trickle Mode Constant Current Mode Constant Voltage Mode Inhibit TIMEOUT Input Voltage Battery Voltage Charge Current Power Dissipation ISL6292B |
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