TMUX1109: Input protection, clamp to VDD/VSS ?

Jesper Svanfeldt

Part Number: TMUX1109
Other Parts Discussed in Thread: TVS2701

We want to use TMUX1109 in a project and the TMUX has VS, VD max of VDD+0.5V. Is there any internal clamp-diodes on the input of the TMUX1109?

We have 6.8kohm in series with the input and BAV199 external clamp diodes to VDD/VSS. The Vf of the BAV199 is up to 0.7V so this might go over TMUX1109 spec of VDD+0.5V. Is this ok?

See schematic below.

over 4 years ago

0 Clemens Ladisch over 4 years ago

Guru 292450 points

VDD+0.5V implies a silicon diode (its forward voltage is smaller for very small currents).

You should put the resistor between the external diode and the chip so that the internal diode does not see the full overvoltage.

0 Parker Dodson over 4 years ago

TI__Mastermind 48057 points

Hi Jesper,

There are clamping diodes as indicated by Clemens - but they are there mainly for ESD strikes and to be safe adding another resistor to limit the current going into the port during that 0.7V overvoltage event - keeping the voltage seen at the pin within maximum ratings.

Best,

Parker Dodson

0 Jesper Svanfeldt over 4 years ago in reply to Parker Dodson

Prodigy 30 points

Thank you for your answers!

Ok, that confirms what i suspected. There is a TVS2701 in front of the 6.8k resistor so this limits max current into MUX to approx 4mA. Is this to much for internal diodes?If so I was planning to split the 6.8k into two resistors and put BAV199 in between them.

0 Clemens Ladisch over 4 years ago in reply to Jesper Svanfeldt

Guru 292450 points

There is no absolute maximum rating for the diodes on the analog I/Os. In theory, no current is allowed, but in practice, there is that 30 mA value for the digitial inputs. I'd try to stay below 1 mA (which is a somewhat random value).

Schottky diodes (e.g., BAT54S) would have a lower forward voltage.

0 Jesper Svanfeldt over 4 years ago in reply to Clemens Ladisch

Prodigy 30 points

Ok, then splitting the 6.8k in two with BAV199 in between is the way to go. Since we need low leakage the BAT54 is not suitable.

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TMUX1109: Input protection, clamp to VDD/VSS ?