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LTC4011EFE Datasheet(PDF) 10 Page - Linear Technology |
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LTC4011EFE Datasheet(HTML) 10 Page - Linear Technology |
10 / 24 page 10 LTC4011 4011p OPERATIO Shutdown State The LTC4011 remains in micropower shutdown until DCIN (Pin 1) is driven above VCC (Pin 8). In shutdown all status and PWM outputs and internally generated termi- nations or supply voltages are inactive. Current consump- tion from VCC and BAT is reduced to a very low level. Charge Qualification State Once DCIN is greater than VCC, the LTC4011 exits mi- cropower shutdown, enables its own internal supplies, provides VRTvoltagefortemperaturesensing,andswitches VCDIV to GND to allow measurement of the average single- cell voltage. The IC also verifies that VCC is at or above 4.25V, VCC is 500mV above BAT and VCELL is between 350mV and 1.95V. If VCELL is above 1.95V, the fault state is entered, which is described in more detail below. Once adequate voltage conditions exist for charging, READY is asserted. If the voltage between VTEMP and GND is below 200mV, the LTC4011 is paused. If VTEMP is above 200mV but below 2.85V, the LTC4011 verifies that the sensed tem- perature is between 5°C and 45°C. If these temperature limits are not met or if its own die temperature is too high, the LTC4011 will indicate a fault and not allow charging to begin. If VTEMP is greater than 2.85V, battery temperature related charge qualification, monitoring and termination are disabled. Once charging is fully qualified, precharge begins (unless the LTC4011 is paused). In that case, the VTEMP pin is monitored for further control. The charge status indicators and PWM outputs remain inactive until charging begins. Charge Monitoring The LTC4011 continues to monitor important voltage and temperature parameters during all charging states. If the DC input is removed, charging stops and the shutdown state is entered. If VCC drops below 4.25V or VCELL drops below 350mV, charging stops and the LTC4011 returns to the charge qualification state. If VCELLexceeds1.95V,charg- ing stops and the IC enters the fault state. If an external thermistor indicates sensed temperature is beyond a range of 5°C to 60°C, or the internal die temperature exceeds an internal thermal limit, charging is suspended, the charge timer is paused and the LTC4011 indicates a fault condi- tion. Normal charging resumes from the previous state when the sensed temperature returns to a satisfactory range. In addition, other battery faults are detected during specific charging states as described below. Precharge State If the initial voltage on VCELL is below 900mV, the LTC4011 enters the precharge state and enables the PWM current source to trickle charge using one-fifth the programmed charge current. The CHRG status output is active during precharge. The precharge state duration is limited to tMAX/12 minutes, where tMAX is the maximum fast charge period programmed with the TIMER pin. If sufficient VCELL voltage cannot be developed in this length of time, the fault state is entered, otherwise fast charge begins. Fast Charge State If adequate average single-cell voltage exists, the LTC4011 enters the fast charge state and begins charging at the programmed current set by the external current sense resistor connected between the SENSE and BAT pins. The CHRG status output is active during fast charge. If VCELL is initially above 1.325V, cell voltage processing begins immediately. Otherwise –∆V termination is disabled for a stabilization period of tMAX/12. In that case, the LTC4011 makes another fault check at tMAX/12, requiring the aver- age cell voltage to be above 1.22V. This ensures the battery pack is accepting a fast charge. If VCELL is not above this voltage threshold, the fault state is entered. Fast charge state duration is limited to tMAX and the fault state is entered if this limit is exceeded. 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 network is present, chemistry-specific limits for ∆T/∆t (rate of temperature rise) are also used in the termination algorithm. Temperature-based termination, if enabled, becomes active as soon as the fast charge state is entered. (Refer to Figure 1) |
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