Definition: Overvoltage Inputs are signals that exceed the normal operating voltage range of the digital isolator. If this is not properly managed, the excessive voltage can cause damage to the IC and cause malfunction of the system.
What is an overvoltage tolerant digital isolator?
Digital isolators with overvoltage tolerant inputs, such as the ISO6441, can allow for the input pins to handle voltages beyond the supply voltage.
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| Input Stage of Digital Isolator (ISO6741) | Input Stage of Digital Isolator with Overvoltage Tolerant Inputs (ISO6441) |
Digital isolators with overvoltage tolerant inputs include an additional diode in the reverse direction. When VCCI is powered off, the 1MΩ pull-up resistor is inactive and the reverse diode (circled in red) prevents the input signal to drive current to VCCI. This means that an input signal can be driven even if VCCI is powered off.
How can you tell if your digital isolator has overvoltage tolerant inputs?
The input voltage specification under the absolute maximum ratings can indicate overvoltage tolerant inputs.
In datasheets of digital isolator, such as ISO6741, we can see that the input voltage is VCC+0.5V (shown below). This means that the input voltage is dependent on the VCC supply voltage. Crossing this specification violates the absolute maximum ratings and can cause damage to the device.
In datasheets of digital isolators with overvoltage tolerant inputs, we can see that the input voltage is -0.5V to 6V (shown below). Unlike the ISO6741, the input voltage is a numerical value and not dependent of the supply voltage. This means that the input signal can be applied even when supply voltage is powered off, as long as the applied signal is within absolute maximum ratings.
What TI Digital Isolators offer overvoltage tolerant inputs?
Currently, TI offers the ISO6441 and the ISO6163. The ISO64xx and ISO61xx digital isolator families are TI's newest generation of digital isolators, offering overvoltage tolerant inputs along with various other benefits. Please check the product pages of these devices below for more information:
ISO6441 data sheet, product information and support | TI.com
ISO6163 data sheet, product information and support | TI.com
For any related questions, please check the Isolation E2E page, Frequently Asked Questions: Isolation , or reach out to the team on the Isolation Forum!
