Other Parts Discussed in Thread: UCD90320U, , CSD15380F3
Any recommended MOSFET for Inhibit pin for ON/OFF configuration ? LMZ31503 have to be interfaced with UCD90320u
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Any recommended MOSFET for Inhibit pin for ON/OFF configuration ? LMZ31503 have to be interfaced with UCD90320u
No specific recommended MOSFET. You can even interface directly to GPIO, as shown in this reference design where INH pin is directly driven by UCD90120A-1 GPIO pins.
Can you tell me what is the range of voltage that is visible at INHIBIT? (To what value this pin is pulled up internally?)
Hi Karthik,
If floated, EN will be pulled up to around 3V. The EN pin itself has abs max rating of 6V which should not be violated.
Taking a brief look at the UCD90320u datasheet section 8.4.5, it appears you should be able to set its GPIO outputs as open-drain, which would be a good option for interfacing to the LMZ31503 INH pin.
Regards,
Kris
But some issues are there involved with it.
1. In your datasheet "https://www.ti.com/lit/ds/symlink/lmz31503.pdf?&ts=1589868780837" in page number 4 It was mentioned that ". A small low leakage (<300 nA) MOSFET is recommended for control" .But UCD90320U have leakage current around 1uA.
2.The VIN used is greater than 10V and in your datasheet in page number 20 it was mentioned that "The Inhibit control has its own internal pull-up to VIN potential"
Can you recommend a mosfet for this usage? Can CSD15380F3 can be used?
Hi Karthik,
Yes, CSD15380F3 could be used. Regarding your other points
1. I did not see this GPIO leakage spec in the UCD90320U datasheet. I mentioned another reference design using another UCD monitor/sequencer with its GPIO directly interfacing to the LMZ31503 inhibit without issue. That UCD90320U leakage seems high, but if that is correct, then using the CSD15380F3 is a good option.
2. This description is not accurate, perhaps the intent was to say that the 3V is derived from Vin as well. I will note it down as something that needs to be clarified. I looked at characterization data on the controller used in the module to confirm the ~3V value. In Figure 30 and 31 on page 20, the orange VINH signals is the voltage at the INH pin, not the gate of the external FET, and you can see that the signal goes to 3V when the external FET is off.
Regards,
Kris
Hi Karthik, what questions need further clarification after my response on May 20?
Karthik, the internal INH pull-up current source goes to an internally generated 3V, not Vin. This can be seen in the the datasheet waveforms Figure 30 and 31.