Wide-Input, High-Frequency, Triple-Output Supplies with Voltage Monitor and Power-On Reset

The MAX8513/MAX8514 integrate a voltage-mode PWM step-down DC-DC controller and two LDO controllers, a voltage monitor, and a power-on reset for the lowest-cost power-supply and monitoring solution for xDSL modems, routers, gateways, and set-top boxes.

The DC-DC controller switching frequency can be set with an external resistor from 300kHz to 1.4MHz, to allow for the optimization of cost, size, and efficiency. For noisesensitive applications, the DC-DC controller can also be synchronized to an external clock, minimizing noise interference. Operation above 1.1MHz reduces noise for high data-rate xDSL applications. An adjustable soft-start and adjustable foldback current limit provide reliable startup and fault protection. The DC-DC controller output voltage can be set externally to a voltage from 1.25V to 5.5V. Current limiting is accomplished by inductor current sensing for improved efficiency, or by an external sense resistor for better accuracy.

The MAX8513/MAX8514s' first LDO controller is designed to provide a low-cost, high-current regulated output from 0.8V to 5.5V using an N-channel MOSFET or a low-current output using a low-cost NPN transistor. The MAX8513's second regulator can be used to generate 0.8V to 27V output with a low-cost PNP transistor. Both LDO regulators can operate either from the DC-DC controller output or from a higher voltage derived with a flyback overwinding on the DC-DC converter inductor. The MAX8514's second LDO regulator is designed to provide a negative output with an NPN transistor.

A sequence input allows the outputs to either power up together, or for the DC-DC regulator to power up first and each LDO controller to power up in sequence. An input power-fail output (active-low PFO) is provided for input power-fail warning, such as in dying-gasp applications. A power-on reset circuit with a 140ms delay is also included to indicate when all outputs have achieved regulation and stabilized.

Applications

* Set-Top Boxes * Wireless Routers * xDSL, Cable, ISDN Modems, and Routers

* Low-Cost DC-DC Controller with Two LDOs

* Wide Input Range: 4.5V to 28V

* 300kHz to 1.4MHz Adjustable Switching Frequency

* Low Noise for High Data-Rate xDSL Applications

* Synchronizable to External Clock

* Adjustable Soft-Start

* Lossless Adjustable Foldback Current Limit

* Power-On Reset with 140ms Delay

* Adjustable Input Power-Fail Warning for Dying Gasp

* Selectable Output-Voltage Sequencing or Output-Voltage Tracking