ORing MOSFET Controllers with Fastest Fault Isolation for Redundant Power Supplies

Critical loads often employ parallel-connected power supplies with redundancy in order to enhance system reliability. The MAX8535/MAX8536/MAX8585 are highly integrated but inexpensive MOSFET controllers that provide isolation and redundant power capability in high-reliability systems. The MAX8535/MAX8585 are used in 12V systems, and have an internal charge pump to drive the gates of the n-channel pass elements to VCC + 10V. The MAX8536 is used in 3.3V and 5V systems, with a chargepump output of VCC + 5V.

During startup, the MAX8535/MAX8536/MAX8585 monitor the voltage drop across external MOSFETs. Once VCC approaches or exceeds the bus voltage, the MOSFETs are turned on. The MAX8535/MAX8536/MAX8585 feature a dual-purpose TIMER input. A single external resistor from TIMER to ground sets the turn-on speed of the external MOSFETs. Optionally, the TIMER input can be used as a logic-enable pin. Once the device is turned on, the MAX8535/MAX8536/MAX8585 monitor the load, protecting against overvoltage, undervoltage, and reverse-current conditions.

Overvoltage and undervoltage fault thresholds are adjustable and can be disabled. The current-limit trip points are set by the external MOSFETs' RDS(ON), reducing component count. An open-drain logic-low fault output indicates if an overvoltage, undervoltage, or reverse-current fault occurs.

All devices come in a space-saving 8-pin µMAX® package and are specified over the extended -40°C to +85°C temperature range.

Applications

* Network/Telecom Power Supplies * On-Board Redundant Power Supplies in Blade Servers * Rectifiers * Redundant Power Supplies in High-Availability Systems * Silver Box Supplies for Servers

* Simple, Integrated, and Inexpensive ORing MOSFET Controller

* ORing MOSFET Drive for 12V (MAX8535/MAX8585) and 3.3V or 5V (MAX8536) Bus

* Eliminates ORing Diode Power Dissipation and Reverse Leakage Current

* Provides N + 1 Redundant Supply Capability for Highly Reliable Systems

* Isolates Failed Supply from Output Bus in <1µs

* Reverse-Current Flow Detection

* Programmable Soft-Start

* Logic-Enable Input

* Adjustable Overvoltage and Undervoltage Trip Points

* Fault-Indicator Output

* Space-Saving 8-Pin µMAX Package