LMP8640HV: LMP8640HV Design Question

Hi John,

during the switchings, do you see a ringing at the -IN pin which goes negative? This could destroy U11. Put an unidirectional TVS in parallel to VR4 to prevent the voltage at the -IN pin from going negative. Connect this unidirectional TVS, C40 and VR4 close to the -IN pin and to the local GND. Use a solid ground plane for the local GND connections arround the LMP8640HV.

Kai

Hello John,

Thanks for considering to use Texas Instruments. This transient you see from the inductive kickback, how large is it? If it is greater than -6V, you likely have damaged the LMP8640HV. Below is a table from the datasheet that specifies the max voltages the +IN and -IN can handle without causing permanent damage.

If we look at section 7.7 of the datasheet, we can find the device output range as shown below. Although a common mode voltage is specified at 2.1V, I believe that for the entire common mode operating range the minimum output should always be between the device ground and the device supply.

If your transient exceeds -6V, you may want to consider installing a tvs diode as kai noted above or at least a flyback diode.

As for output filter overdamping, I do not think that would destroy the downstream MCU. However, it will have an impact on how fast the LMP8640HV output slews and the bandwidth of the signal reaching your MCU.