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The LTC( )1700 is a current mode synchronous step-up DC/DC controller that drives external N-channel and P-channel power MOSFETs using a constant frequency PWM architecture. Current limiting is provided by sensing the voltage drop across the main MOSFET, eliminating the need of a sense resistor. This No RSENSE(TM) technique helps the LTC1700 maintain high efficiency at heavy loads while Burst Mode operation ensures high efficiency at light loads, thus providing high efficiencies over a wide range of load currents.
The LTC1700 operates at a minimum input voltage as low as 0.9V. The device boasts a ±1.5% output voltage accuracy and consumes only 200µA of quiescent current. In shutdown, it only draws 10µA.
To prevent inductor current runaway, the duty cycle is limited to 90%. Overvoltage protection is also provided which shuts both the external MOSFETs off when tripped.
High constant operating frequency of 530kHz allows the use of small inductors and output capacitors. The LTC1700 can also be synchronized between 400kHz to 750kHz. Burst Mode operation is inhibited when the device is externally clocked or when the SYNC/MODE pin is pulled low to reduce noise and RF interference.
如图 （a）是采用LTC1700的3.3V变换为5V的升压变换器电路，输出电流达到3A，负载电流为Z00mA～3A的范围时变换效率高于90%，负载电流降到3mA时变换效率保持在80%。微型封装的LTC1700在数字摄影机或其他电池供电的设各中用作高效率升压变换器。图9－52
