Minimizing ripple is the charge of two dual, step-down, switch-mode power-supply (SMPS) controllers with synchronous rectification for main 5/3.3-V power generation in battery-powered notebooks. They can reduce input ripple current across an input voltage range up to the 26-V maximum through fixed-frequency operation with optimal interleaving. For output current limiting, they can be used with a sense resistor, or for minimum dissipation, a lossless inductor. Housed in a 32-pin TQFN, the MAX1533 has internal 5- and 3.3-V linear regulators that also power their gate drivers. In addition, external keep-alive loads run at a total of 100 mA. When the main pulse-width-modulation (PWM) regulators are in regulation, automatic bootstrap switches bypass those internal linear regulators and provide currents up to 200 mA from each linear output. Housed in a 36-pin TQFN, the MAX1537 adds an adjustable, internal 150-mA linear regulator typically used with a secondary winding to provide a 12-V supply. MAX1533 prices start at $5.10, and MAX1537 prices start at $5.20, both for quantities of 1000 units and up. Evaluation kits are available.
Maxim Integrated Products