Datasheet LT3652HV (Analog Devices) - 10

LT3652HV
APPLICATIONS INFORMATION Overview
monitor the battery voltage while in standby, and if that LT3652HV is a complete monolithic, mid-power, multi- voltage falls 2.5% from the full-charge float voltage, the chemistry buck battery charger, addressing high input LT3652HV engages an automatic charge cycle restart. The voltage applications with solutions that require a minimum IC also automatically restarts a new charge cycle after a of external components. The IC uses a 1MHz constant fre- bad battery fault once the failed battery is removed and quency, average-current mode step-down architecture. replaced with another battery. The LT3652HV incorporates a 2A switch that is driven The LT3652HV contains provisions for a battery tem- by a bootstrapped supply to maximize efficiency during perature monitoring circuit. This feature monitors battery charging cycles. Wide input range allows operation to full temperature using a thermistor during the charging cycle. charge from voltages as high as 34V. A precision threshold If the battery temperature moves outside a safe charg- shutdown pin allows incorporation of UVLO functionality ing range of 0°C to 40°C, the IC suspends charging and using a simple resistor divider. The IC can also be put into signals a fault condition until the temperature returns to a low-current shutdown mode, in which the input supply the safe charging range. bias is reduced to only 15µA. The LT3652HV contains two digital open-collector outputs, The LT3652HV employs an input voltage regulation loop, which provide charger status and signal fault conditions. which reduces charge current if a monitored input voltage These binary-coded pins signal battery charging, standby falls below a programmed level. When the LT3652HV is or shutdown modes, battery temperature faults, and bad powered by a solar panel, the input regulation loop is used battery faults. to maintain the panel at peak output power.
General Operation (See Block Diagram)
The LT3652HV automatically enters a battery precondition The LT3652HV uses average current mode control loop mode if the sensed battery voltage is very low. In this mode, architecture, such that the IC servos directly to average the charge current is reduced to 15% of the programmed charge current. The LT3652HV senses charger output maximum, as set by the inductor sense resistor, RSENSE. voltage through a resistor divider via the V Once the battery voltage reaches 70% of the fully charged FB pin. The difference between the voltage on this pin and an internal float voltage, the IC automatically increases maximum 3.3V voltage reference is integrated by the voltage error charge current to the full programmed value. amplifier (V-EA). This amplifier generates an error volt- The LT3652HV can use a charge-current based C/10 age on its output (ITH), which corresponds to the average termination scheme, which ends a charge cycle when current sensed across the inductor current sense resistor, the battery charge current falls to one tenth of the pro- RSENSE, which is connected between the SENSE and BAT grammed maximum charge current. The LT3652HV also pins. The ITH voltage is then divided down by a factor of contains an internal charge cycle control timer, for timer- 10, and imposed on the input of the current error amplifier based termination. When using the internal timer, the (C-EA). The difference between this imposed voltage and IC combines C/10 detection with a programmable time the current sense resistor voltage is integrated, with the constraint, during which the charging cycle can continue resulting voltage (VC) used as a threshold that is compared beyond the C/10 level to top-off a battery. The charge against an internally generated ramp. The output of this cycle terminates when a specific time elapses, typically 3 comparison controls the charger’s switch. hours. When the timer-based scheme is used, the IC also The I supports bad battery detection, which triggers a system TH error voltage corresponds linearly to average current sensed across the inductor current sense resistor, fault if a battery stays in precondition mode for more than allowing maximum charge current control by limiting the one eighth of the total charge cycle time. effective voltage range of ITH. A clamp limits this voltage Once charging is terminated, the LT3652HV automati- to 1V which, in turn, limits the current sense voltage to cally enters a low-current standby mode where supply 100mV. This sets the maximum charge current, or the bias currents are reduced to 85µA. The IC continues to current delivered while the charger is operating in con- 3652hvfb 10 For more information www.linear.com/LT3652HV Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Applications Information Typical Applications Package Description Revision History Typical Application Related Parts