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LT3652EMSETRPBF Datasheet(PDF) 10 Page - Linear Technology |
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LT3652EMSETRPBF Datasheet(HTML) 10 Page - Linear Technology |
10 / 26 page LT3652 10 3652fb APPLICATIONS INFORMATION Overview LT3652 is a complete monolithic, mid-power, multi-chem- istry buck battery charger, addressing high input voltage applications with solutions that require a minimum of exter- nal components. The IC uses a 1MHz constant frequency, average-current mode step-down architecture. The LT3652 incorporates a 2A switch that is driven by a bootstrapped supply to maximize efficiency during charging cycles. Wide input range allows operation to full charge from voltages as high as 32V. A precision threshold shutdown pin allows incorporation of UVLO functionality using a simple resistor divider. The IC can also be put into a low-current shutdown mode, in which the input supply bias is reduced to only 15μA. The LT3652 employs an input voltage regulation loop, which reduces charge current if a monitored input volt- age falls below a programmed level. When the LT3652 is powered by a solar panel, the input regulation loop is used to maintain the panel at peak output power. The LT3652 automatically enters a battery precondition mode if the sensed battery voltage is very low. In this mode, the charge current is reduced to 15% of the programmed maximum, as set by the inductor sense resistor, RSENSE. Once the battery voltage reaches 70% of the fully charged float voltage, the IC automatically increases maximum charge current to the full programmed value. The LT3652 can use a charge-current based C/10 termina- tion scheme, which ends a charge cycle when the battery charge current falls to one tenth of the programmed maximum charge current. The LT3652 also contains an internal charge cycle control timer, for timer-based termina- tion. When using the internal timer, the IC combines C/10 detection with a programmable time constraint, during which the charging cycle can continue beyond the C/10 level to top-off a battery. The charge cycle terminates when a specific time elapses, typically 3 hours. When the timer-based scheme is used, the IC also supports bad battery detection, which triggers a system fault if a battery stays in precondition mode for more than one eighth of the total charge cycle time. Once charging is terminated, the LT3652 automatically enters a low-current standby mode where supply bias currents are reduced to 85μA. The IC continues to monitor the battery voltage while in standby, and if that voltage falls 2.5% from the full-charge float voltage, the LT3652 engages an automatic charge cycle restart. The IC also automatically restarts a new charge cycle after a bad bat- tery fault once the failed battery is removed and replaced with another battery. The LT3652 contains provisions for a battery temperature monitoring circuit. This feature monitors battery tempera- ture using a thermistor during the charging cycle. If the battery temperature moves outside a safe charging range of 0°C to 40°C, the IC suspends charging and signals a fault condition until the temperature returns to the safe charging range. The LT3652 contains two digital open-collector outputs, which provide charger status and signal fault conditions. These binary-coded pins signal battery charging, standby or shutdown modes, battery temperature faults, and bad battery faults. General Operation (See Block Diagram) The LT3652 uses average current mode control loop architecture, such that the IC servos directly to average charge current. The LT3652 senses charger output voltage through a resistor divider via the VFB pin. The difference between the voltage on this pin and an internal 3.3V volt- age reference is integrated by the voltage error amplifier (V-EA). This amplifier generates an error voltage on its output (ITH), which corresponds to the average current sensed across the inductor current sense resistor, RSENSE, which is connected between the SENSE and BAT pins. The ITH voltage is then divided down by a factor of 10, and imposed on the input of the current error amplifier (C-EA). The difference between this imposed voltage and the current sense resistor voltage is integrated, with the resulting voltage (VC) used as a threshold that is compared against an internally generated ramp. The output of this comparison controls the charger’s switch. |
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