Datasheet LT3650-4.1, LT3650-4.2 (Analog Devices) - 10

LT3650-4.1/LT3650-4.2
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 to the C/10 current level, the IC will indicate a fully charged 1V which, in turn, limits the current sense voltage to 100mV. battery status, but the charger will continue to source This sets the maximum charge current, or the current low currents into the battery until the programmed EOC delivered while the charger is operating in constant-current time has elapsed, at which time the charge cycle will (CC) mode, which corresponds to 100mV across RSENSE. terminate. At EOC, when the charging cycle terminates, if This maximum charge current level can also be manipu- the battery did not achieve at least 97.5% of the full float lated through the RNG/SS pin (see the RNG/SS: Dynamic voltage, charging is deemed unsuccessful. The LT3650 Charge Current Adjust and RNG/SS: Soft-Start sections). will then re-initiate, and charging will continue for another If the voltage on the BAT pin is below V full timer cycle. BAT(PRE), the LT3650 engages precondition mode. During the precondition inter- Use of the timer function also enables bad-battery detec- val, the charger continues to operate in constant-current tion. This fault condition is achieved if the battery does mode, but the maximum charge current is reduced to 15% not respond to preconditioning and the charger remains of the maximum programmed value as set by RSENSE. in (or enters) precondition mode after one-eighth of the When the charger output voltage on the BAT pin approaches programmed charge cycle time. A bad-battery fault halts the float voltage (VBAT(FLT)), the charger transitions into the charging cycle, the CHRG status pin goes high imped- constant-voltage (CV) mode, and charge current is reduced ance and the FAULT pin is pulled low. from the maximum value. As this occurs, the ITH voltage When the LT3650 terminates a charging cycle, whether falls from the limit clamp and servos to lower voltages. through C/10 detection or by reaching timer EOC, the The IC monitors the ITH voltage as it is reduced, and average current mode analog loop remains active but detection of the C/10 charge current is achieved when the internal float voltage reference is reduced by 2.5%. ITH = 0.1V. If the charger is configured for C/10 termina- Because the voltage on a successfully charged battery is tion, this threshold is used to terminate the charge cycle. at the full float voltage, the voltage error amp detects an Once the charge cycle is terminated, the CHRG status overvoltage condition and rails low. When the voltage er- pin becomes high impedance and the charger enters low ror amp output drops below 0.3V, the IC enters standby current standby mode. mode, where most of the internal circuitry is disabled, and The LT3650 contains an internal charge cycle timer that the VIN bias current is reduced to 85µA. When the voltage terminates a successful charge cycle after a programmed on the BAT pin drops below the reduced float reference amount of time. This timer is typically programmed to level, the output of the voltage error amp will climb, at achieve end-of-cycle (EOC) in three hours, but can be which point the IC comes out of standby mode and a new configured for any amount of time by setting an appropriate charging cycle is initiated. 36504142fc 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