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LTC4010 Datasheet(PDF) 11 Page - Linear Technology |
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LTC4010 Datasheet(HTML) 11 Page - Linear Technology |
11 / 24 page LTC4010 4010fb operaTion (Refer to Figure 1) Charge Termination Fast charge termination parameters are dependent upon the battery chemistry selected with the CHEM pin. Volt- age-based termination (–∆V) is always active after the initial voltage stabilization period. If an external thermistor networkispresent,chemistry-specificlimitsfor∆T/∆t(rate of temperature rise) are also used in the termination algo- rithm.Temperature-basedtermination,ifenabled,becomes active as soon as the fast charge state is entered. Successful charge termination requires a charge rate between C/2 and 2C. Lower rates may not produce the batteryvoltageandtemperatureprofilerequiredforcharge termination. Top-Off Charge State If NiMH fast charge termination occurs because the ∆T/∆t limit is exceeded after an initial period of tMAX/12 has expired, the LTC4010 enters the top-off charge state. Top-off charge is implemented by sourcing one-tenth the programmed charge current for tMAX/3 minutes to ensure that 100% charge has been delivered to the battery. The CHRG status output is active during the top-off state. If NiCd cells have been selected with the CHEM pin, the LTC4010 never enters the top-off state. Automatic Recharge State Once charging is complete, the automatic recharge state is entered to address the self-discharge characteristics of nickel chemistry cells. The charge status output is inactive during automatic recharge, but VCDIV remains switched to GND to monitor the average cell voltage. If the VCELL voltage drops below 1.325V without falling below 350mV, the charge timer is reset and a new fast charge cycle is initiated. The internal termination algorithms of the LTC4010 are adjusted when a fast charge cycle is initiated from auto- matic recharge, because the battery should be almost fully charged.Voltage-basedterminationisenabledimmediately and the NiMH ∆T/∆t limit is fixed at a battery temperature rise of 1°C/minute. Fault State Asdiscussedpreviously,theLTC4010entersthefaultstate based on detection of invalid battery voltages during vari- ous charging phases. The IC also monitors the regulation of the PWM control loop and will enter the fault state if this is not within acceptable limits. Once in the fault state, the battery must be removed or DC input power must be cycled in order to initiate further charging. In the fault state, the FAULT output is active, the READY output is inactive, charging stops and the charge indicator output is inactive. The VCDIV output remains connected to GND to allow detection of battery removal. Note that the LTC4010 also uses the FAULT output to indi- cate that charging is suspended due to invalid battery or internal die temperatures. However, the IC does not enter the fault state in these cases and normal operation will resume when all temperatures return to acceptable levels. Refer to the Status Outputs section for more detail. Insertion and Removal of Batteries TheLTC4010automaticallysensestheinsertionorremoval of a battery by monitoring the VCELL pin voltage. Should this voltage fall below 350mV, the IC considers the bat- tery to be absent. Removing and then inserting a battery causes the LTC4010 to initiate a completely new charge cycle beginning with charge qualification. External Pause Control After charging is initiated, the VTEMP pin may be used to pause operation at any time. When the voltage between VTEMP and GND drops below 200mV, the charge timer pauses, fast charge termination algorithms are inhibited and the PWM outputs are disabled. The status and VCDIV outputs all remain active. Normal function is fully restored from the previous state when pause ends. |
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