IC Protections
Introduction
Integrated circuits are very sensitive to voltage spikes; power regulators has input and output electrical limits. In real world electronic operation, transients and sudden changes of power loads are quite common. To ensure the ICs are protected against these unforeseen variability of electrical voltage and current, proper IC protection circuits needs to be designed in order to enhance the readability of the product.
Types of Protections
ESD/High Voltage Transients
Transient voltage suppressor (TVS) diode
Purpose
Protect IC pins with transient voltage spikes
bidirectional protection is commonly used because voltage spikes can be either positive or negative.
Where to place them?
Place one for each connected pins of a connector
For high speed lines, specialized low capacitance TVS diode is needed.
For power rails, choose a TVS that has larger current sinking capabilities.
Over Voltage Protection (OVP)
Purpose
This circuit protects input voltage of a IC pin to be under it's maximum tolerable voltage in order to avoid electrical damage. OCP circuits works by monitoring voltage level going to the IC pin, and disconnects IC pin from transient source when voltage threshold is exceeded.
Where to place them
It commonly used for power supply input, so placed it right in front of the power supply regulator,
Over Current Protection (OCP)
Purpose
protect power supply regulator output
reduce risk of frying the electronics
Where to place them?
Place at output for a regulator that is sourcing power to external device
example, for device supporting USB OTG function that requires the device to be used as a power source for any USB connected device such as a USB camera, placing the OCP circuit at the output the USB OTG power regulator protects device's regulator.
Note: OCP circuit comes with user settable current limit, which shall set to comply with maximum OTG current limit standard.
Reverse Voltage protection (RVP)
Purpose
protect power supply regulator output when input voltage polarity is inversed
reduce risk of frying the electronics
Where to place them?
Place near the input power connector
E-Fuse
Purpose
It's resetaable electronic fuse that trips when a output fault occurs (i.e., high current draw from the load) and the recovers to normal condition when the fault recovers (often temperature monitoring is also included in the e-fuse circuit, where the temperature of the system needs to be cool down before the Fuse resets itself.
Where to place them?
Place at output of the load where fuse is needed to protect the system from frying all together.
In Rush Current Limit Protection
Purpose
It limits the amount of inrush current of a power supply (e.g. AC wall adapter) when its output is connected to an electronic device.
The reason that the power supply sees a inrush current is that when an external device is turned on is that there are a lot of uncharged capacitors on the input power rails of electronic device. At the moment when device is plugged in, empty capacitor draws high amount of current causing a large inrush current , this will result power supply voltage to droop quickly, and can cause IC brownout (i.e system reset) before the embedded system can fully being powered on.
Generally a discrete soft start circuit can be used.
Note: a lot of power supply regulator has softstart features so it will ramp its output at a adjustable ramp rate (slew rate)
Another technique is avoid inrush current is selectively turn on different electronics as a define power on sequence to distribute load current across time.
Where to place them?
at Input connector pin that supplies a system power supply regulator
at the output of a power regulator that has many different loads.
Summary and Conclusion
TVS diodes are used to protect signal lines and power rails at connector side from ESD or transient voltage spikes.
OVP and OCP protects electronics circuits from being damaged.
In rush current protection ensures proper power on sequence without overloading any power regulator output.
OCP, OVP, in rush current protection are the three most common protection circuits that are used by electronics system engineers. However different components (e.g. fuse to OCP, NTC resistor for inrush current, transformer for transient voltages, etc.) are used for protection with higher voltage and current electronics, but the basic protections scheme is the same.