Electronic Design

TechView: Analog & Power -- More Li-Ion Charger ICs

Maxim Integrated Products (www.maxim-ic.com) has made the USB battery-charging option available in a tiny five-pin SOT23 package. The company offers two such devices, the MAX1551/MAX1555 USB/ac-adapter, single-cell lithium-ion (li-ion) battery chargers. These chips operate from input voltages up to 7 V and require no external FETs or diodes.

When USB power is connected without dc power, the charge current is set to 100 mA (max). This allows for charging from both powered and unpowered USB hubs without requiring port communication. When both dc and USB power are connected, charging current is set at 340 mA (typical). No input-blocking diodes are required to prevent battery drain. A power-OK output on the 1551 indicates when input power is present, and a charge output on the 1555 indicates charging status. On-chip thermal regulation regulates charge current based on charger die temperature. Prices start at $0.85 each.

Maxim also introduced two linear one-cell li-ion battery chargers in 3- by 3-mm eight-pin TDFNs. The MAX1507/MAX1508 are distinguished by input overvoltage protection up to 14 V. In addition, they integrate a power MOSFET, a reverse-blocking diode, and a current-sense resistor.

These devices accept a 4.25- to 13-V supply, but they disable charging when the input voltage exceeds 7 V to protect against unqualified or faulty ac adapters. The chips fast-charge at up to 0.8 A and include a charge-current monitor and a charge-status indicator. The MAX1507 provides three selectable thermal-regulation setpoints, and the MAX1508 has an ac-adapter detection output. The MAX1507/MAX1508 start at $2.12.

Advanced Analogic Technologies (www.analogictech.com) also announced a linear battery-charge controller that accepts input voltages as high as 15 V. The AAT3680 supports one- or two-cell li-ion packs in all charging modes, including an optional fast trickle charge at a 2X rate to accelerate the charge cycle. This device integrates circuits for overvoltage, overcurrent, and overtemperature protection.

In addition to the usual LED status output, the AAT3680 features a 1-MHz serial interface that transmits the battery status to the system host. The controller can operate with a low-cost external pnp transistor or a p-channel power MOSFET. It’s offered in either an eight-pin MSOP or a 12-pin TSOPJW, which cost $1.63 and $1.87, respectively.

Another single-cell li-ion charger IC comes from Linear Technology (www.linear.com). The LTC4002 standalone switch-mode charger accepts inputs over a wide 4.7- to 24-V range, which lets the charger operate from any wall adapter while eliminating the need for the input transient protection that’s normally required with adapters that deliver 9 V or higher. Other features include automatic shutdown, battery preconditioning, battery temperature sensing, an end-of-charge indicator, and a three-hour charge termination timer.

The LTC4002 contains a current-mode pulse-width-modulation controller that switches at 500 kHz. Using an external sense resistor, charge current is programmed with an accuracy of ±5%. In addition, the accuracy on the 4.2-V final float voltage is ±1%. This charger is offered in a 3- by 3-mm DFN or an eight-pin SOP. Pricing starts at $1.95.

An earlier announcement last spring from National Semiconductor (www.national.com) included details about two li-ion/nickel-metal-hydride chargers, the LP3945 and LP3946. These devices feature on-chip pass transistors. The LP3945 is programmable through an I2C interface, while the LP3946 is preprogrammed at the factory. The I2C interface allows programming of the charging current, the end-of-charge current, and the voltage-regulation output. The LP3945 also supports a linear regulator mode when the charger input is present and the battery isn’t attached. Housed in 14-pin LLPs, the LP3945 and LP3946 cost $0.98 and $0.90 each, respectively, in quantities of 500,000.

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