Features: ` Low 450mA Peak Battery Current Provides 2A, 5V GSM Burst
` 90% Efficiency
` Internal Power MOSFETs and Current-Sense Resistor
` Output Disconnects from Input During Shutdown
` 3A Shutdown Current
` Precise Voltage-Controlled Current Limit (MAX1687)
` Adaptive Constant-Recharge-Time Capability (MAX1688)
` 1.25V to 6V Adjustable Output
` 2.7V to 6V Input Range (1 Li-Ion cell or 3 NiMH cells)
` Switching Frequency Can Exceed 1MHz
` Standby Mode Disables DC-DC During Transmission Burst
` Low Inrush Current at Start-UpApplication · GSM Phones
· Wireless Handsets
· PC Cards (PCMCIA)Pinout
SpecificationsIN, ON, LX1, CHG, LIM, FB, OUT, REF to GND .......-0.3V to +7V
LX2 to GND .........................................................-0.3V to +8V
IN, LX1 Average Current.....................................................1A
Continuous Power Dissipation (TA = +70°C)
TSSOP (derate 5.7mW/°C above +70°C) ...................457mW
SO (derate 5.88mW/°C above +70°C)........................471mW
Operating Temperature Range ......................-40°C to +85°C
Storage Temperature Range .......................-65°C to +150°C
Lead Temperature (soldering, 10sec) .......................+300° C
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
DescriptionThe MAX1687/MAX1688 step-up DC-DC converters deliver up to 2W from a single Li-Ion or three NiMH cells. The devices are ideal for burst-load applications such as GSM cell phones and wireless LANs, where the RF power amplifiers require short, high current bursts. The MAX1687/MAX1688 reduce battery surge current by slowly charging a reservoir capacitor, which supplies the necessary peak energy for the load current burst. As a result, the peak battery current is limited, thus maximizing battery life and minimizing battery voltage sag and transient dips.
An internal synchronous rectifier provides over 90% conversion efficiency and eliminates the need for an external Schottky diode. A logic shutdown mode reduces the shutdown current to only 3A. The devices can be disabled during current bursts (RF transmit mode) to eliminate switching noise.
The switching frequency of the MAX1687/MAX1688, controlled by the selected inductor, can exceed 1MHz. Two external resistors set the output voltage from 1.25V to 6V. The MAX1687 controls peak battery current, while the MAX1688 features a more advanced, adaptive constantrecharge- time algorithm that maximizes battery life. The MAX1687/MAX1688 are available in thin 16-pin TSSOP (1.1mm max height) or standard 8-pin SO packages.
MAX1687 Data Sheet
