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MAX1909 Datasheet(PDF) 18 Page - Maxim Integrated Products |
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MAX1909 Datasheet(HTML) 18 Page - Maxim Integrated Products |
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18 / 30 page  Multichemistry Battery Chargers with Automatic System Power Selector 18 ______________________________________________________________________________________ The input range for ICTL is 0 to 3.6V on the MAX1909, and 0 to 3.2V on the MAX8725. The charger shuts down if ICTL is forced below 0.75V for the MAX1909 and 0.06V for the MAX8725. When choosing current-sense resistor RS2, note that it must have a sufficient power rating to handle the full-load current. The sense resistor’s I2R power loss reduces charger efficiency. Adjusting ICTL to drop the voltage across the current-sense resistor improves efficiency, but may degrade accuracy due to the current-sense amplifier’s input offset error. The charge-current error amplifier (GMI) is compensated at the CCI pin. See the Compensation section. Conditioning Charge The MAX1909 includes a battery voltage comparator that allows a conditioning charge of overdischarged Li+ battery packs. If the battery-pack voltage is less than 3.1V x the number of cells programmed by CELLS, the MAX1909 charges the battery with 300mA current when using sense resistor RS2 = 0.015Ω. After the battery voltage exceeds the conditioning charge threshold, the MAX1909 resumes full-charge mode, charging to the programmed voltage and current limits. The MAX8725 does not provide automatic support for providing a conditioning charge. To configure the MAX8725 to provide a conditioning charge current, ICTL should be directly driven. Setting the Input Current Limit The total input current, from a wall cube or other DC source, is the sum of the system supply current and the current required by the charger. The MAX1909/MAX8725 reduce the source current by decreasing the charge cur- rent when the input current exceeds the set input current limit. This technique does not truly limit the input current. As the system supply current rises, the available charge current drops proportionally to zero. Thereafter, the total input current can increase without limit. An internal amplifier compares the differential voltage between CSSP and CSSN to a scaled voltage set with the CLS input. VCLS can be driven directly or set with a resistive voltage-divider between REF and GND. Connect CLS to REF to set the input current-limit sense voltage to the maximum value of 75mV. Calculate the input current as follows: VCLS determines the reference voltage of the GMS error amplifier. Sense resistor RS1 sets the maximum allowable source current. Once the input current limit is reached, the charge current is decreased linearly until the input current is below the desired threshold. Duty cycle affects the accuracy of the input current limit. AC load current also affects accuracy (see the Typical Operating Characteristics). Refer to the MAX1909/MAX8725 EV kit data sheet for more details on reducing the effects of switching noise. When choosing the current-sense resistor RS1, carefully calculate its power rating. Take into account variations in the system’s load current and the overall accuracy of the sense amplifier. Note that the voltage drop across RS1 contributes additional power loss, which reduces efficiency. System currents normally fluctuate as portions of the system are powered up or put to sleep. Without input current regulation, the input source must be able to deliver the maximum system current and the maximum charger input current. By using the input current-limit circuit, the output current capability of the AC wall adapter can be lowered, reducing system cost. Current Measurement The MAX1909/MAX8725 include an input current monitor IINP. The current delivered at the IINP output is a scaled- down replica of the system load current plus the input- referred charge current that is sensed across CSSP and CSSN inputs. The output voltage range is 0 to 3V. The voltage of IINP is proportional to the input current according to the following equation: VIINP = ISOURCE ✕ RS1 ✕ GIINP ✕ R9 where ISOURCE is the DC current supplied by the AC adapter power, GIINP is the transconductance of IINP (3mA/V typ), and R9 is the resistor connected between IINP and ground. Leave the IINP pin unconnected if not used. LDO Regulator LDO provides a 5.4V supply derived from DCIN and can deliver up to 10mA of extra load current. The low- side MOSFET driver is powered by DLOV, which must be connected to LDO as shown in Figure 1. LDO also supplies the 4.2235V reference (REF) and most of the control circuitry. Bypass LDO with a 1µF capacitor. Shutdown and Charge Inhibit ( PKPRES) When the AC adapter is removed, the MAX1909/ MAX8725 shut down to a low-power state that does not significantly load the battery. Under these conditions, a maximum of 6µA is drawn from the battery through the combined load of the SRC, CSSP, CSSN, CSIP, CSIN, and BATT inputs. The charger enters this low-power state when DCIN falls below the undervoltage-lockout (UVLO) threshold of 7V. The PDS switch turns off, the PDL switch turns on, and the system runs from the battery. I RS V V IN CLS REF =× 0 075 1 . |
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Similar Description - MAX1909 |
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