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DC / USB Power Adapter Application Example

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DC / USB Power Adapter Application Example

At present, USB interface power adapters can be found everywhere, and many occasions use USB power adapters to power low-voltage electrical appliances, so there are many low-voltage circuits powered by USB power adapters. But how can I use electrical appliances that are powered by a USB power adapter? This article introduces the power management chip launched by Qiqi Company recently. Both devices have an independent power manager, an ideal diode controller and an independent high-voltage switch battery. Charger for portable USB power adapter. Their switching topology takes into account various input situations, including high-voltage power supplies up to 36V (40V maximum), such as 12VAC / DC AC adapters, FireWire ports, or automotive batteries. In addition, they also accept low-voltage power sources such as 5V AC adapters or USB inputs and single-cell lithium-ion / lithium polymer batteries.
A typical application circuit based on LTC4085 is shown in Figure 1 and Figure 2. In Figure 1, LTC4085 is a 5V power supply that can be directly connected to 5V AC power and USB. After 100mA or 500mA selection by the control end HPWR, the output voltage is controlled by the GATE and ACPR ends. This control output can be directly output to the battery for power supply and charging via the BAT pin.
The LTC4085 is a monolithic autonomous power manager, ideal diode controller, and stand-alone linear battery charger for portable USB power adapters. LTC4085 has PowerPath control function, which can supply power to the system load from USBVBUS or AC adapter power. To comply with the USB power adapter current limit specifications, the LTC4085 will automatically reduce the battery charge current when the system load current increases. In order to ensure that a fully charged battery is in an unused state when it is connected to the bus, the IC transmits power to the load through the USB bus instead of taking power from the battery. Once the power is removed, current will flow from the battery to the load through a 200mΩ internal low-loss ideal diode, minimizing voltage drops and power consumption. An on-board circuit is provided to drive an optional external GATEPFET connection device to reduce the total impedance of the ideal diode below 30mΩ if the application requires it.
The unique feature of the LTC4085 is to detect the access of the AC adapter and use it as a backup power source to charge the battery while supplying power to the system load. The LTC4085 also provides an option to charge the battery at a higher rating (up to 1.5A) than the allowable value of the USB power adapter specification when the AC adapter is connected, which can greatly increase the battery charging speed. . The total charge time for charge termination is set by an external resistor. When the charge current decreases, the charge timer period will automatically extend to ensure that the battery is always fully charged. Additional features include automatic recharge, NTC thermistor input, automatic switch to battery when AC adapter input is removed, inrush current limit, reverse current isolation, undervoltage lockout, and thermal adjustment.
The floating voltage of LTC4085 is preset to 4.2V, and the guaranteed accuracy in the temperature range of 0 to 85 ° C is 0.8%. The charging current can be easily set with a resistor. For battery preconditioning and proper temperature charging certification, a fully discharged battery will be trickle charged automatically at 10% of the programmed current until the battery voltage exceeds 2.8V.
A typical application circuit based on LTC4089 is shown in Figure 3 and Figure 4. In Figure 3, the switching regulator has a BAT-Track adaptive output control function, which greatly improves the efficiency of the battery charger that can provide a 1.2A charge current, because the output voltage of the switching regulator automatically tracks the battery Voltage. The LTC4089 provides a fixed 5V output from a high-voltage input for charging a single-cell lithium-ion / polymer battery. The floating voltage of the battery charger is preset to 4.2V, and the accuracy is guaranteed to be 1.0% in the temperature range of 0 to 85 ° C. The charging current can be easily set via a resistor. The total charge time for charge termination is set by an external capacitor and provides a C / 10 charge current detection output. Additional features include automatic thermal adjustment, NTC thermistor input for suitable temperature charging, automatic recharging of the battery, reverse galvanic isolation and undervoltage lockout.

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| Release time: 2019.12.27 Source:
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Dongguan Qiqi Industrial Co., Ltd. specializes in producing: power adapters , chargers, LED drive power supplies, car chargers, switching power supplies, etc ...