microcontroller protection

[786]

microcontroller input protection

how a microcontroller can be protected by voltage surges or spikes irrespective of use of regulated power supply - also regulators used in power supply have diodes in reverse? so what components to be used for protection of microcontrollers - using simple regulated power supply - is there any need to change power supply or to add additional protection circuitry for microcontroller? please help
thanks in advance.

 

[banjo]

For voltage surges on external pin connections, typically a varistor is used. Now they make these in very small surface mount packages.

http://doc.chipfind.ru/littelfuse/v200ch8.htm

Two popular manufacturers are Littelfuse and Murata.

For the actual power supply pins, the typical method is to connect a zener diode as a clamp across the power supply output. For a 5V supply, a 6V zener can be used. The idea is that should the voltage ever get to 6V, the zener will conduct limiting the voltage. Since there is nothing to limit the current, the zener will be destroyed if the surge last long enough. This is by design, and considered a sacrifical component.

The reverse biased diodes you see in linear requlator schematics are not there to protect the microcontroller. Their purpose is to protect the regulator. During power off, if the input capacitor to the linear regulator drops in voltage faster than the output capacitor, then the regulator becomes reverse biased. This can blow the internal pass transistor of the regulator. The external diode provides a path to equalize the input and output capacitor voltages during turnoff and protects the regulator.

 

[btbass]

input pin protection site:edaboard.com

In the automotive industry, circuits have to pass very severe votage spikes on the micro input pins.
Most micros have internal clamp diodes on the I/O pins. To limit the current into a pin configured as an input, we normally have a series resistor in the line close to the input pin, typical value of 33K. Output pins are not as susceptable to noise spikes.
Connectors to the outside world normally have 1n 200V Ceramic caps as close to the connector pin as possible to ground.
Voltage regulators are available that are automotive qualified with in-built surge and static discharge protection.
Minimum package size for resistors/Caps connected to the outside world are 0805. (Safer pad spacing).

 

[H_u_n_t_e_r]

site:www.edaboard.com

Most micros have internal clamp diodes on the I/O pins. To limit the current into a pin configured as an input, we normally have a series resistor in the line close to the input pin, typical value of 33K.(Safer pad spacing).

It should be 33R not 33K
Actually 100R is better.

 

[btbass]

microcontroller protection voltage

No, it should be 33K!
The units have to work while having 8KV discharges on the outside world connector pins, the units have to survive 15K static discharges on the outside world connector pins.
The input impedence into the micro pin is very high. The 33K series resistor does not intefere with it's function.

33R would do nothing to protect the pin.