LTM4609 sudden death issues - any possible causes?

Hi mikep-j, 

Some things that can cause failure for the LTM4609 are listed below.

1. Inductor current exceeding its saturation current rating (especially if hard-saturating ferrite)

2. Layout issues such as :

    - Not kelvin sensing directly across the current sense resistor with Sense+/Sense-

    - Not having a sufficiently low impedance path for the high current coming out of the Rsense bank and through the sense resistor to PGND.

      Use plenty of vias if sense resistor is not on the same layer next to the module (ie on opposite layer).

3. Current sense resistor itself and/or layout has significant equivalent series inductance. Please use low ESL type & kelvin sensing. 

4. Loop stability margins insufficient (ie unstable switching). 

High peak inductor currents can cause excessive internal mosfet stress, which eventually can cause mosfets to fail short if not limited properly by the current sense loop. The current sensing signal must be kept clean. The current through the resistor is high and slew rate is fast so requires a low ESL sensing resistor and good kelvin sense routing for it to the sense pins as shown in the datasheet. If not, noise spikes in the signal can cause the current comparator to trip at an improper time leading to high peak current stress conditions in the module. 

For your application, you may also want to reach out to your local Field Applications Engineer / Sales to make sure you have the best module  solution to date for your power with battery backup requirements. 

Thanks 

Hi mikep-j, 

Some things that can cause failure for the LTM4609 are listed below.

1. Inductor current exceeding its saturation current rating (especially if hard-saturating ferrite)

2. Layout issues such as :

    - Not kelvin sensing directly across the current sense resistor with Sense+/Sense-

    - Not having a sufficiently low impedance path for the high current coming out of the Rsense bank and through the sense resistor to PGND.

      Use plenty of vias if sense resistor is not on the same layer next to the module (ie on opposite layer).

3. Current sense resistor itself and/or layout has significant equivalent series inductance. Please use low ESL type & kelvin sensing. 

4. Loop stability margins insufficient (ie unstable switching). 

High peak inductor currents can cause excessive internal mosfet stress, which eventually can cause mosfets to fail short if not limited properly by the current sense loop. The current sensing signal must be kept clean. The current through the resistor is high and slew rate is fast so requires a low ESL sensing resistor and good kelvin sense routing for it to the sense pins as shown in the datasheet. If not, noise spikes in the signal can cause the current comparator to trip at an improper time leading to high peak current stress conditions in the module. 

For your application, you may also want to reach out to your local Field Applications Engineer / Sales to make sure you have the best module  solution to date for your power with battery backup requirements. 

Thanks