Quick-PWM Slave Controllers for Multiphase, Step-Down Supplies

The MAX1887/MAX1897 step-down slave controllers are intended for low-voltage, high-current, multiphase DC-to-DC applications. The MAX1887/MAX1897 slave controllers can be combined with any of Maxim's Quick-PWM™ step-down controllers to form a multiphase DC-to-DC converter. Existing Quick-PWM controllers, such as the MAX1718, function as the master controller, providing accurate output voltage regulation, fast transient response, and fault protection features. Synchronized to the master's low-side gate driver, the MAX1887/MAX1897 include the Quick-PWM constant on-time controller, gate drivers for a synchronous rectifier, active current balancing, and precision current-limit circuitry.

The MAX1887/MAX1897 provide the same high efficiency, ultra-low duty factor capability, and excellent transient response as other Quick-PWM controllers. The MAX1887/MAX1897 differentially sense the inductor currents of both the master and the slave across current-sense resistors. These differential inputs and the adjustable current-limit threshold derived from an external reference allow the slave controller to accurately balance the inductor currents and provide precise current-limit protection. The MAX1887/MAX1897's dual-purpose current-limit input also allows the slave controller to automatically enter a low-power standby mode when the master controller shuts down.

The MAX1887 triggers on the rising edge of the master's low-side gate driver, which staggers the on-times of both master and slave, providing out-of-phase operation that can reduce the input ripple current and consequently the number of input capacitors. The MAX1897 features a selectable trigger polarity, allowing out-of-phase or simultaneous in-phase operation.

Applications

* CPU Core Supplies * Notebook Computers * Servers/Desktop Computers * Single-Stage (BATT to VCORE) Converters * Telecom * Two-Stage (+5V to VCORE) Converters

* Quick-PWM Slave Controller

* Precise, Active Current Balance (±1.25mV)

* Accurate, Adjustable Current-Limit Threshold

* Optimized for Low-Output Voltages (≤ 2V)

* 4V to 28V Battery Input Range

* Fixed 300kHz (MAX1887) or Selectable 200kHz/300kHz/550kHz (MAX1897) Switching Frequency

* Drive Large Synchronous-Rectifier MOSFETs

* 525µA (typ) ICC Supply Current

* 20µA Standby Supply Current

* < 1µA Shutdown (MAX1897) Supply Current

* Small 16-Pin QSOP (MAX1887), Compact 20-Pin 5mm x 5mm QFN (MAX1897), or 20-Pin 5mm x 5mm Thin QFN (MAX1897)