If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

# TCA9539-Q1: Can our device support 0-24V input signal?

Part Number: TCA9539-Q1
Other Parts Discussed in Thread: TCA9539

Dear team,

In BCM design, the input signal will connected to the IO EXPANDER directly, the input signal is 0~24V.

As the IO EXPANDER’s power rail is 3.3V / 5V,  normally the GPIO of IO EXPANDER has a clamp diode to make the circuit safe.

Does our device TCA9539 support such function, input signal is 0-24V?

Thanks & Best Regards,

Sherry

• Sherry,

Looking over the datasheet, the pins have an absolute maximum rating of 6V, anything higher will damage the pin. So 0-24V won't be doable here. Is there a way you can scale down the voltage in the application?

Regards,

Eric Hackett

• Hello Eric, we have a follow up question from customer about the spec of input diode clamp voltage In the datasheet 6.1 there is a data of -1.2V min at the -18mA test condition. However, there is no data to indicate what will happen with the voltage exceeds? Also there is no data of the input diode's clamp voltage and clamp current? Also, what's the function of the clamp voltage? is it for ESD protection? thank you very much.

• Rui,

Thanks for your patience on this, I've notified an expert to look further into this.

Regards,

Eric Hackett

• Hi Rui,

The -1.2V at -18mA tells us that the clamping diodes will have a biasing voltage at -1.2V when you try to pull 18mA out of them. The absolute minimum voltage spec'd for the device is -0.5V so when you pull them below this voltage, you can risk damage (seems like the clamping diode would kick in though). The absolute clamping current tells us that if you exceed -20mA while the clamping diode is biased, you could break the device. I believe this means that if you exceed -0.5V but keep the current below -20mA, the device may likely survive.

-Bobby

• Hi Bobby,

Thanks for your reply! I still have one question here. Our absolute max voltage is 3.6V, if the input signal voltage exceeds 3.6, for example, 12V, the clamping diode can clamp the voltage below 3.6V, is my understanding right?

Thanks & Best Regards,

Sherry

• Hi Sherry,

The clamping diode is there for under voltage protection, it doesn't clamp the voltage at 3.6V. It clamps the voltage depending on the current when the voltage goes below GND. In my experience, these devices will break at ~7V (outside the absolute max we spec) immediately so if you hooked it directly to 12V then the device will break.

-Bobby