Reverse Current Protection in a System

[Barley_Li]

Under specific circuit configurations, output voltage may sometimes rise higher than your input voltage. This will cause a reverse current condition, and risks damage to your circuitry.

There are 3 common ways to protect from reverse current - Diodes, MOSFETs and Load Switches.

Diodes
Diodes provide the simplest and least expensive method of reverse current protection. However, the forward voltage drop across the diode limits Vcc by 0.6V-0.8V for typical diodes and increase the power dissipation in the system.

You can select Schotty Diodes to minimize the forward voltage drop, but they are more expensive. Schotty Diodes also have more reverse current leakage.

MOSFETS
Using 2 MOSFETs connected as shown below is a good way to block the current in both directions when the MOSFETs are turned off. The voltage drop across MOSFETS is lower than the diode solution. The drawback is that this method requires more space on the board to build.

Load Switches
Like MOSFETS, Load switches can block current in both directions when turned off. They also reduce footprint and BOM counts.

For example, TI TPS22963C is a load switch used in a reverse current protection circuit. After the device
is disabled via the ON pin and VOUT is forced to an external voltage, a very small amount of current will flow from VOUT to VIN. This will prevent any extra current loading on the voltage source supplying the external voltage.

For more current protection device information, please check out these other threads on TechForum:

Differences in Circuit Protection Devices

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Using a PTC as a Fuse for Circuit Protection

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