Design Documentation

Powerswitch Module, MBARI 101227

4:36 PM 5/29/01 Dave Wright

General:

The powerswitch module provides four channels of protected highside switching for voltages of ~5V to ~25V. It is intended to act as a circuit breaker and inrush limiter between a battery pack and an auxillary instrument or other component. 

Circuit description:

The IPS511 highside switches, U1 thru U4, provide a ~5 amp current limit. When this limit is exceeded, the status line is pulled low. If the overcurrent condition persists and the die temperature exceeds safe operating limits the ouput will be turned off until the die cools.

Refer to the International Rectifier IPS511 datasheet and the IPS_01 thru _03 documents for more detailed information on device operation.

U5 acts as a simple latch to allow the host controller to turn the IPS511 on, and then monitor its status to determine if an overload has occured. This is accomplished using a bidirectional I/O line from the host controller. Taking the line high will turn the IPS511 on, and keep it in the on state even if it enters current limit mode (within thermal limits). Any inrush current in excess of 5A will be clamped at that level until it subsides. After taking the control line high, if it is then configured as an input, its state can be monitored. When high, it indicates that the switch is on. If it goes low, it is an idication that the device entered the current limit condition and reset the latch. To turn the switch off the control line is taken low and held there. Thus the load, and the switch, are protected without the need for constant monitoring in software. The polling loop that checks for overloads can run at whatever rate is appropriate for the application, without concern for the safety of the switch or load.

Physical:

The module dimensions are 2.200" x 1.50". Mounting holes for #2 machine screws are provided at each corner. All thruhole connectors, and mounting holes, register with a 0.1" grid. This is to facillitate mounting of the module on standard perfboard for prototyping or "one off" construction. Active components are mounted on the "top" side, and power output connectors on the "bottom" (non silkscreen) side. When mounted to a motherboard or other substrate, the component side faces "inward" to allow access to the connectors. Connector P1 contains the signals that are routed to the host microcontroller and power sources.


Assembly Notes:

The connectors for the power outputs, J1 thru J4, mount on the solder side of the board. All other components, including P1, mount on the component (silkscreen) side of the board.



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