Dual 180° Out-of-Phase Buck Controllers with Sequencing/Prebias Startup and POR

The MAX1858A/MAX1875A/MAX1876A dual, synchronized, step-down controllers generate two outputs from input supplies ranging from 4.5V to 23V. Each output is adjustable from sub-1V to 18V and supports loads of 10A or higher. Input voltage ripple and total RMS input ripple current are reduced by synchronized 180° out-of-phase operation.

The switching frequency is adjustable from 100kHz to 600kHz with an external resistor. Alternatively, the controller can be synchronized to an external clock generated by another MAX1858A/MAX1875A/MAX1876A or a system clock. One MAX1858A/MAX1875A/MAX1876A can be set to generate an in-phase, or 90° out-of-phase, clock signal for synchronization with additional controllers. This allows two controllers to operate either as an interleaved two- or four-phase system with each output shifted by 90°. The MAX1858A/MAX1875A/MAX1876A feature soft-start. The MAX1858A also features first-on/last-off power sequencing and soft-stop.

The MAX1858A/MAX1875A/MAX1876A eliminate the need for current-sense resistors by utilizing the low-side MOSFET's on-resistance as a current-sense element. This protects the DC-DC components from damage during output-overload conditions or output short-circuit faults without requiring a current-sense resistor. Adjustable foldback current limit reduces power dissipation during short-circuit conditions. The MAX1858A/MAX1876A include a power-on reset (POR) output to signal the system when both outputs reach regulation.

The MAX1858A/MAX1875A/MAX1876A ensure that the output voltage does not swing negative when the input power is removed or when EN is driven low. The MAX1875A/MAX1876A also allow prebias startup without discharging the output.

The MAX1858A/MAX1875A/MAX1876A are available in a 24-pin QSOP package. Use the MAX1875 evaluation kit or the MAX1858 evaluation kit to evaluate the MAX1858A/MAX1875A/MAX1876A.

Applications

* Broadband Routers * Desknote Computers * DSP, ASIC, and FPGA Power Supplies * Network-Power Supplies * Servers * Set-Top Boxes * Telecom Power Supplies

* 4.5V to 23V Input Supply Range

* 0 to 18V Output Voltage Range (Up to 10A)

* Adjustable Lossless Foldback Current Limit

* Adjustable 100kHz to 600kHz Switching Frequency

* Optional Synchronization

* Clock Output for Master/Slave Synchronization

* 4 x 90° Out-of-Phase Step-Down Converters (Using Two Controllers, Figure 7)

* Prebias Startup (MAX1875A/MAX1876A)

* Power Sequencing (MAX1858A)

* RST-bar Output with 140ms Minimum Delay (MAX1858A/MAX1876A)

* Fixed-Frequency Pulse-Width Modulation (PWM) Operation