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ACT3704YH Datasheet(PDF) 8 Page - Active-Semi, Inc |
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ACT3704YH Datasheet(HTML) 8 Page - Active-Semi, Inc |
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8 / 15 page  ACT3704 Rev2, 26-Jul-07 Innovative Products. Active Solutions. - 8 - www.active-semi.com Copyright © 2007 Active-Semi, Inc. FUNCTIONAL DESCRIPTION The ACT3704 is an intelligent, stand-alone Con- stant-Current, Constant-Voltage control (CC/CV), linear-mode, single-cell charger for Lithium-Based cell chemistries. The device incorporates current and voltage sense circuitry, an internal 12V power MOSFET, a 120°C thermal-regulation loop that mini- mizes total charge time, a complete state-machine that implements charge safety features, and circuitry that eliminates the reverse-blocking diode required by conventional charger designs. The ACT3704 features an accurate charge termina- tion voltage, programmable fast-charge constant current, and a programmable charge safety timeout period. Other features include current-limited nSTAT and nEOC outputs that can directly drive LED indi- cators without external resistors or provide a logic- level status signal to the host microprocessor. CC/CV Regulation Loop At the core of the ACT3704 is a CC/CV regulation loop, which regulates either current or voltage as necessary to ensure fast and safe charging of the battery. In a normal charge cycle, this loop regulates the cur- rent to the value set by RISET. Charging continues at this current until the battery voltage reaches the charge termination voltage. At this point the CV loop takes over, and charge current is allowed to de- crease as necessary to maintain charging at the charge termination voltage. Setting The Charge Termination Voltage The ACT3704 offers two pin-programmable battery termination voltages; connect ADJ to G to select a 4.10V termination voltage, connect ADJ to IN (or to a voltage greater than 1.4V) to select a 4.20V termi- nation voltage. Charge Current Programming The maximum charging current is programmed by an external resistor (RISET) connected from ISET to G. Calculate RISET as follows: Where IBAT is Amps. The voltage at ISET is fixed at 1.20V, and the maxi- mum charge current at BAT is set by: The RISET values in Table 1 are standard 1%. Note that the actual charging current may be limited to a current that is lower than the programmed fast- charge current due to the ACT3704’s internal ther- mal-regulation loop. See the Thermal Regulation Loop section for more information. Thermal Regulation Loop The ACT3704 features an internal thermal regula- tion loop that reduces the charging current as nec- essary to ensure that the die temperature does not rise beyond the thermal regulation threshold of 120°C. This feature protects the ACT3704 against excessive junction temperature and makes the ACT3704 more accommodating to aggressive ther- mal designs. Note, however, that attention to good thermal designs is required to achieve the fastest possible charge time by maximizing charge current. In order to account for the extended total charge time resulting from operation in thermal regulation mode, the charge timeout periods are extended proportionally to the reduction in charge current. In order to ensure a safe charge, the maximum time- out periods are limited to 2x the room temperature values. The conditions that cause the ACT3704 to reduce charge current in accordance to the internal thermal regulation loop can be approximated by calculating the power dissipated in the part. Most of the power dissipation is generated from the internal charge MOSFET (Q1 in the Functional Block Diagram). The power dissipation is calculated to be approxi- mately: Table 1: Charge Current Programming RISET(kΩ) Charge Current (mA) 89 297 64 413 56 470 47 562 33 800 27 989 () ISET BAT R / V 20 . 1 Ω k 22 I × = (2) () BAT ISET I / V 20 . 1 Ω k 22 R × = (1) ( ) BAT BAT IN D I V - V P × = (3) PD is the power dissipated, VIN is the input supply voltage, VBAT is the battery voltage and IBAT is the charge current. The approximate ambient tempera- |
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