BQ24751ARHDR

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BQ24751ARHDR Application Field and Working Principle

The BQ24751ARHDR is a fully integrated high performance primary lithium-ion (Li+) battery charger, suitable for space-limited portable applications. The device operates from an input voltage range between 4.5 V and 21 V and is capable of charging single-cell Li-ion battery, such as prismatic, cylindrical, pouch, and button cell. It can also be used with other chemistry like LiFePO4, higher capacity Li-ion cells and standard, and fast charge batteries.

The device allows for highest power conversion through its fast-charge circuit architecture. It also features a low quiescent current, automatic detection of inserted Li-ion battery type, automatic power-path management, internal thermal temperature monitor, external signal monitor, and low total cost of ownership. The low part count and limited external components enable a small total design size, making it perfect for portable applications.

Application Field

The BQ24751ARHDR is suitable to charge low-cost Li-ion batteries over a 4.5 V to 21 V input voltage range. It provides automatic charging current regulation and charge termination, as well as output current regulation, making it an ideal choice for handheld products such as cell phones, media players and tablets.

It can also be used in battery powered products such as portable medical devices, power tools and robotics, providing a cost effective, high performance and end-of-charge detection.

Working Principle

The BQ24751ARHDR has both an input current regulator (ILIM) and input voltage regulator (VIN) that control the input current and voltage, respectively. The maximum input current is limited by the ILIM resistor, while the maximum input voltage is limited by the VIN capacitor. The output current is limited by the input current and can be set with the external resistor selection.

The BQ24751ARHDR then powers the lithium-ion battery through an internal low RDS(ON) switch in pulse-width modulation (PWM) control. When the input voltage is higher than the voltage of the battery, the PWM charging is active, providing constant current to the battery. When the input voltage is lower than the battery voltage, the switch is disabled and the battery is discharged.

The charge process is monitored by an automaticshutoff circuit, which samples the battery voltage level, input voltage level and temperature. During the charging process, the charge current is regulated based on the battery voltage level and input voltage level. When the battery voltage reaches the regulation point, the current regulator reduces the battery current to a trickle charge level.

The BQ24751ARHDR also has an internal temperature monitor. If the temperature of the battery or charger exceeds a preset value, the output of the charger will be disabled until the temperature drops below the threshold. The internal temperature monitor can be used to limit the maximum temperature of the battery, providing protection against thermal runaway.

The BQ24751ARHDR provides a complete, low cost reliable charging solution for primary Li+ battery-powered portable applications.

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