Another boost regulator example may be found in the MAX1705 and MAX1706 family of high-efficiency, low-noise, step-up DC-DC converters with an auxiliary linear-regulator output. As discussed previously, 3.6V lithium cells typically require a buck-boost topology to cover their lifetime voltage range. These converters, however, combine boost and linear regulators, and the linear output is a very low-noise supply as well. Using a 300kHz synchronous rectifier PWM boost topology, the ICs can generate a 2.5V to 5.5V output from a battery input, such as 1 to 3 NiCd/NiMH cells or 1 Li-Ion cell. They provide a regulated output over their entire operating voltage range. The MAX1705 has a 1A n-channel MOSFET switch, while the MAX1706 has a 0.5A switch. Minimum VIN is 1.1V and they have a 1μA shutdown mode.
The linear regulator in both devices delivers up to 200mA. An efficiency-enhancing track mode reduces the step-up DC-DC converter output to 300mV above the linear-regulator output. Compared to similar non-synchronous converters, these converters provide 5% better efficiency. To enhance efficiency at light loads, they feature a pulse-frequency-modulation standby mode. Both devices come in a 16-pin QSOP package and have two shutdown-control inputs for push-on/push-off control, along with an uncommitted comparator that can be used as a voltage monitor. To evaluate the ICs for various battery-powered designs, you can check out the MAX1705 evaluation kit.
