Datasheet LT3650-8.2, LT3650-8.4 (Analog Devices) - 10

LT3650-8.2/LT3650-8.4
operaTion
The ITH error voltage corresponds linearly to average cur- timing capacitor value (CTIMER). When timer termination rent sensed across the inductor current sense resistor, is used, the charge cycle does not terminate after C/10 allowing maximum charge current control by limiting the is achieved. Because the CHRG status pin responds to effective voltage range of ITH. A clamp limits this voltage the C/10 current level, the IC will indicate a fully charged to 1V which, in turn, limits the current sense voltage to battery status, but the charger will continue to source 100mV. This sets the maximum charge current, or the low currents into the battery until the programmed EOC current delivered while the charger is operating in constant- time has elapsed, at which time the charge cycle will current (CC) mode, which corresponds to 100mV across terminate. At EOC, when the charging cycle terminates, if RSENSE. This maximum charge current level can also be the battery did not achieve at least 97.5% of the full float manipulated through the RNG/SS pin (see the RNG/SS: voltage, charging is deemed unsuccessful. The LT3650 Dynamic Charge Current Adjust and RNG/SS: Soft-Start will then re-initiate, and charging will continue for another sections). full timer cycle. If the voltage on the BAT pin is below VBAT(PRE), the LT3650 Use of the timer function also enables bad-battery detec- engages precondition mode. During the precondition inter- tion. This fault condition is achieved if the battery does val, the charger continues to operate in constant-current not respond to preconditioning and the charger remains mode, but the maximum charge current is reduced to 15% in (or enters) precondition mode after one-eighth of the of the maximum programmed value as set by RSENSE. programmed charge cycle time. A bad-battery fault halts When the charger output voltage on the BAT pin approaches the charging cycle, the CHRG status pin goes high imped- the float voltage (VBAT(FLT)), the charger transitions into ance, and the FAULT pin is pulled low. constant-voltage (CV) mode, and charge current is reduced When the LT3650 terminates a charging cycle, whether from the maximum value. As this occurs, the ITH voltage through C/10 detection or by reaching timer EOC, the falls from the limit clamp and servos to lower voltages. average current mode analog loop remains active but The IC monitors the ITH voltage as it is reduced, and the internal float voltage reference is reduced by 2.5%. detection of the C/10 charge current is achieved when Because the voltage on a successfully charged battery is ITH = 0.1V. If the charger is configured for C/10 termina- at the full float voltage, the voltage error amp detects an tion, this threshold is used to terminate the charge cycle. overvoltage condition and rails low. When the voltage er- Once the charge cycle is terminated, the CHRG status ror amp output drops below 0.3V, the IC enters standby pin becomes high impedance and the charger enters low mode, where most of the internal circuitry is disabled, and current standby mode. the VIN bias current is reduced to 85µA. When the voltage The LT3650 contains an internal charge cycle timer that on the BAT pin drops below the reduced float reference terminates a successful charge cycle after a programmed level, the output of the voltage error amp will climb, at amount of time. This timer is typically programmed to which point the IC comes out of standby mode and a new achieve end-of-cycle (EOC) in three hours, but can be charging cycle is initiated. configured for any amount of time by setting an appropriate 36508284fd 10 Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Typical Applications Package Description Revision History Typical Application Related Parts