MAX1965

19-2084; Rev 0; 7/01 Tracking/Sequencing Triple/Quintuple Power-Supply Controllers General Description The MAX1964/MAX1965 power-supply controllers are designed to address cost-sensitive applications demanding voltage sequencing/tracking, such as cable modem consumer premise equipment (CPE), xDSL CPE, and set-top boxes. Operating off a low-cost, unregulated DC supply (such as a wall adapter output), the MAX1964 generates three positive outputs and the MAX1965 generates four positive outputs and one negative output to provide an inexpensive system power supply. The MAX1964 includes a current-mode synchronous step-down controller and two positive regulator gain blocks. The MAX1965 has one additional positive gain block and one negative regulator gain block. The main synchronous step-down controller generates a highcurrent output that is preset to 3.3V or adjustable from 1.236V to 0.75 ✕ VIN with an external resistive-divider. The 200kHz operating frequency allows the use of lowcost aluminum-electrolytic capacitors and low-cost power magnetics. Additionally, the MAX1964/MAX1965 step-down controllers sense the voltage across the lowside MOSFET’s on-resistance to efficiently provide the current-limit signal, eliminating the need for costly current-sense resistors. The MAX1964/MAX1965 generate additional supply rails at low cost. The positive regulator gain blocks use an external PNP pass transistor to generate low voltage rails directly from the main step-down converter (such as ...