Datasheet LT3652 (Analog Devices) - 10

LT3652
APPLICATIONS INFORMATION Overview
Once charging is terminated, the LT3652 automatically LT3652 is a complete monolithic, mid-power, multi-chem- enters a low-current standby mode where supply bias istry buck battery charger, addressing high input voltage currents are reduced to 85µA. The IC continues to monitor applications with solutions that require a minimum of exter- the battery voltage while in standby, and if that voltage nal components. The IC uses a 1MHz constant frequency, falls 2.5% from the full-charge float voltage, the LT3652 average-current mode step-down architecture. engages an automatic charge cycle restart. The IC also automatically restarts a new charge cycle after a bad bat- The LT3652 incorporates a 2A switch that is driven by tery fault once the failed battery is removed and replaced a bootstrapped supply to maximize efficiency during with another battery. charging cycles. Wide input range allows operation to full charge from voltages as high as 32V. A precision threshold The LT3652 contains provisions for a battery temperature shutdown pin allows incorporation of UVLO functionality monitoring circuit. This feature monitors battery tempera- using a simple resistor divider. The IC can also be put into ture using a thermistor during the charging cycle. If the a low-current shutdown mode, in which the input supply battery temperature moves outside a safe charging range bias is reduced to only 15µA. of 0°C to 40°C, the IC suspends charging and signals a fault condition until the temperature returns to the safe The LT3652 employs an input voltage regulation loop, charging range. which reduces charge current if a monitored input volt- age falls below a programmed level. When the LT3652 is The LT3652 contains two digital open-collector outputs, powered by a solar panel, the input regulation loop is used which provide charger status and signal fault conditions. to maintain the panel at peak output power. These binary-coded pins signal battery charging, standby or shutdown modes, battery temperature faults, and bad The LT3652 automatically enters a battery precondition battery faults. mode if the sensed battery voltage is very low. In this mode, the charge current is reduced to 15% of the programmed
General Operation (See Block Diagram)
maximum, as set by the inductor sense resistor, RSENSE. The LT3652 uses average current mode control loop Once the battery voltage reaches 70% of the fully charged architecture, such that the IC servos directly to average float voltage, the IC automatically increases maximum charge current. The LT3652 senses charger output voltage charge current to the full programmed value. through a resistor divider via the VFB pin. The difference The LT3652 can use a charge-current based C/10 termina- between the voltage on this pin and an internal 3.3V volt- tion scheme, which ends a charge cycle when the battery age reference is integrated by the voltage error amplifier charge current falls to one tenth of the programmed (V-EA). This amplifier generates an error voltage on its maximum charge current. The LT3652 also contains an output (ITH), which corresponds to the average current internal charge cycle control timer, for timer-based termina- sensed across the inductor current sense resistor, RSENSE, tion. When using the internal timer, the IC combines C/10 which is connected between the SENSE and BAT pins. detection with a programmable time constraint, during The ITH voltage is then divided down by a factor of 10, which the charging cycle can continue beyond the C/10 and imposed on the input of the current error amplifier level to top-off a battery. The charge cycle terminates (C-EA). The difference between this imposed voltage and when a specific time elapses, typically 3 hours. When the current sense resistor voltage is integrated, with the the timer-based scheme is used, the IC also supports bad resulting voltage (VC) used as a threshold that is compared battery detection, which triggers a system fault if a battery against an internally generated ramp. The output of this stays in precondition mode for more than one eighth of comparison controls the charger’s switch. the total charge cycle time. 3652fe 10 For more information www.linear.com/LT3652 Document Outline Description Typical Application Absolute Maximum Ratings Pin Configuration Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Applications Information Package Description Typical Application Related Parts