TPS1HC100-Q1: TVS diode for clamping

Hi Salil,

We have used external Vds clamps to "undercut" the internal clamp in some applications. The trace/pad inductance is minimal.

Since the external load is pulling the output voltage low, the external Vds clamp will trigger first. I have not personally seen the edge case event you are describing, but in such an event if the Vds voltage flies large enough for the internal Vds to trigger, this predicates that the voltage difference would be large enough for the external Vds to clamp or start clamping. Since the internal path is more resistive than the external path, current will shunt through the external path and the voltage will recover to the external clamp level reducing any time duration where it would flow through the internal path.

Thanks,

Shreyas

Hi Salil,

1. The single pulse energy for TPS1HC30-Q1 is 65mJ and this was tested at 13.5V, Ta=125C and with a 1.5mH load.

2. Inductive dissipation occurs when the device is OFF. In normal circumstances when the device is ON, the device protects itself by turning off and reducing the energy dissipated such as thermal shutdown. Since this cannot occur during inductive turn off, large energy stresses on the device can lead to degradation of the FET and a reduction of lifetime. It can also lead to device damage. Therefore, if the load is expected to be heavily inductive in nature, we recommend the use of external clamping.

Thanks,

Shreyas

Hi Salil,

1. We have no dedicated recommendation. External clamping can be achieved by using a TVS from output to GND as shown in this example of an industrial device:

A TVS diode in series with a Schottky is used to avoid conduction during normal operation.

Another option is to use a TVS diode from the VS pin to the VOUT pin. This is essentially to build an external drain to source clamp just like the clamp within the device. 

In both cases, the recommendation is to select a clamp that triggers before the internal clamp. Please check the device datasheet to view the minimum Vds clamp level.

2. Usually ESD diodes do not have the power capability required to demagnetize an inductive load. We recommend using external TVS clamps.

Thanks,

Shreyas

Hi Salil,

No special layout considerations are needed but we do expect this TVS device to see all the inductive energy. Therefore, it would be beneficial to place the TVS close to the device and to make sure there is sufficient copper on the board to act as a heatsink.

The minimum Vds clamp voltage for TPS1HC30-Q1 is 33V across temperature. We have seen TVS diodes available in specific voltage offerings. I would suggest 24V TVS diodes. This should have a breakdown voltage around 28V or so which is further away from 33V. If you are able to find a higher voltage TVS diode, this is also acceptable but do note that often the breakdown voltage is a little higher than the clamp voltage and to effectively circumvent the internal diode, the TVS must trigger first.

Thanks,

Shreyas

Hi Salil,

1. Only our industrial portfolio has non Vds clamp versions. All our automotive device have an integrated clamp.

2. For an external clamp across VS and Vout a Schottky can be used to block the reverse conduction path in the event reverse polarity is a concern. But this is not necessary since the FET turns on in the reverse condition to conduct as well. A Schottky can be place before the device and act as the upstream reverse protection for the device as a whole eliminating the need for a GND network.

3. The output of the device is compatible to go as low as the Vds clamp allows. For example if the voltage is 12V and if the Vds clamp is 40V, during turn off, the output voltage is expected to reach -28V before the clamp kicks in. The device is built to handle these inductive negative spikes. 

Thanks,

Shreyas