Datasheet LTC4020 (Analog Devices) - 9

LTC4020
pin FuncTions
is terminated or when charge current is below the C/10 During CC/CV or lead-acid charging algorithms, a bad bat- threshold. tery fault is generated if the battery voltage does not reach If the LTC4020 is configured for a CC charging algorithm, the precondition threshold voltage within 1/8 of TEOC, or: the STAT1 pin is pulled low during the entire charging TPRE = CTIMER • 1.82 x 106. cycle. The STAT1 pin becomes high impedance when the A 0.2µF capacitor is typically used for CC/CV charging, charge cycle is terminated. which generates a 2.9 hour timer TEOC, and a precondition If the LTC4020 is configured for a lead-acid charging limit time of 22 minutes. A 0.47µF capacitor is typically algorithm, the STAT1 pin is used as a charge cycle stage used for a lead-acid charger, which generates a 6.8 hour indicator pin, and pulled low during the bulk and absorp- absorption stage safety timeout. tion charging stages. The pin is high impedance during the
RNG/SS (Pin 15):
Battery Charge Current Programming float charging period and during NTC or bad battery faults. Pin. This pin allows dynamic adjustment of maximum See Applications Information section. charge current, and can be used to employ a soft-start
STAT2 (Pin 13):
Open-collector status output, typically function. pulled up through a resistor to a supply voltage. This sta- Setting the voltage on the RNG/SS pin reduces maximum tus pin can be pulled up to voltages as high as 55V when charge current from the value programmed. The maximum disabled, and can sink currents up to 1mA when enabled charge current is reduced to the fraction of programmed (<0.4V). Pull down currents as high as 5mA (absolute current (as per the sense resistor, RCS) corresponding maximum) are supported for higher current applications, to the voltage set on the pin (in volts). This pin has an such as lighting LEDs. effective range from 0 to 1V. If the LTC4020 is configured for a CC/CV charging algo- For example, with 0.5V RNG/SS on the pin, the maximum rithms, the STAT2 pin is pulled low during NTC faults or charge current will be reduced to 50% of the programmed after a bad battery fault occurs. value set by the sense resistor values. If the LTC4020 is configured for a CC charging algorithms, 50µA is sourced from the RNG/SS pin, so maximum the STAT2 pin is pulled low during NTC faults. charge current can be programmed by connecting a single If the LTC4020 is configured for a lead-acid charging resistor (RRNG/SS) from RNG/SS to ground, such that the algorithm, the STAT2 pin is used as a charge cycle stage voltage dropped across the resistor is equivalent to the indicator pin, and pulled low during the bulk and float desired pin voltage: charging stages. The pin is high impedance during the VRNG/SS = 50µA • RRNG/SS absorption charging stage and during NTC or bad bat- Soft-start functionality can be implemented by connecting tery faults. a capacitor (CRNG/SS) from RNG/SS to ground, such that See Applications Information section. the time required to charge the capacitor is the desired
TIMER (Pin 14):
End-Of-Cycle Timer Programming Pin. soft-start interval (TSS1). The voltage that corresponds to If a timer based charging algorithm is desired, connect full programmed inductor current on the RNG/SS pin is a capacitor (C 1V, so the relation for this capacitor reduces to: TIMER) from this pin to ground. If no timer functions are desired, connect this pin to ground. CRNG/SS = 50µA • TSS1 End-of-cycle time (in hours) is programmed with the value of CTIMER following the equation: TEOC = CTIMER • 1.46 x 107; 4020fd For more information www.linear.com/LTC4020 9 Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Order Information Electrical Characteristics Pin Configuration Electrical Characteristics Pin Functions Block Diagram Operation Applications Information Package Description Revision History Typical Application Related Parts