Dual-Input USB/AC Adapter 1-Cell Li+ Battery Chargers

General Description
The MAX 1551/MAX 1555 charge a single-cell lithium-ion (Li+) battery from both USB* and AC adapter sources. They operate with no external FETs or diodes, and accept operating input voltages up to 7V.
On-chip thermal limiting simplifies PC board layout and allows optimum charging rate without the thermal limits imposed by worst-case battery and input voltage. When the MAX 1551/MAX 1555 thermal limits are reached, the chargers do not shut down, but progressively reduce charging current.
The MAX1551 includes a POK output to indicate when input power is present. If either charging source is active, POK goes low. The MAX1555 instead features a| CHG output to indicate charging status.
With USB connected, but without DC power, charge current is set to 100mA (max). This allows charging from both powered and unpowered USB hubs with no port communication required. When DC power is connected, charging current is set at 280mA (typ). No input-blocking diodes are required to prevent battery drain.
The MAX1551/MAX1555 are available in 5-pin thin SOT23 packages and operate over a -40°C to +85°C range.