•  
• EDN Europe MAGAZINE
•  
• Free SUBSCRIPTION
• Subscription Renewal
• View Media Kit

• EDN
• EDN Australia
• EDN Asia
• EDN China
• EDN Japan

USB IC charges, supplies and protects

The USB port is fast becoming “the preferred means for portable- device-battery charging” according to Linear Technology—the company notes the need for a charge-management solution that can handle high voltages from automotive, IEEE-1394 or unregulated wall-adapter sources, and protect against over-voltage damage. The default portable-product power source is the single-cell lithium-ion battery, and Linear says the design wish-list includes factors such as high efficiency from high-voltage sources, small external components such as ceramic-only capacitors, good noise immunity, autonomous operation and fast charging with high current densities. Hence, the company’s LTC4098: a chip that charges a lithium-ion cell at up to 1.5A from a wall adapter, or 600 mA from USB and that controls an external regulator to drop the supply it needs from line levels as high as 38V with a 60V transient-withstand rating. The chip is an autonomous high-efficiency power manager, ideal-diode controller and battery charger for portable USBpowered devices. Its switching topology uses Linear’s PowerPath control, which manages power flow between a wall adapter or USB port and the device’s Li-ion/polymer battery while preferentially providing power to the system load. For automotive, IEEE 1394, or other high-voltage applications, “Bat- Track” is the feature that provides control of a companion switching regulator with up to 38V operating input.

The LTC4098 provides an over-voltageprotection circuit up to 66V on the USB input—requiring only an external n-FET/resistor combination—preventing damage that accidental application of high voltage causes. You can provide system power at plug-in even with a dead battery. Its onboard ideal diode guarantees that ample power is always available to V_OUT even if there is insufficient power at the LTC4098’s two input pins. You can use the IC’s ideal diode controller to drive the gate of an optional p-FET, reducing the impedance to the battery to 30m or less. For fast charging, the IC’s switching input stage converts nearly all of the 2.5W available from the USB port to system current, enabling up to 700mA from a 500mA-limited USB port. Packaging is 20-pin 3x4-mm QFN, and operation is from -40 to +85°C.

Linear Technology, www.linear.com