MSPM0L1304: Driving resistive-capacitive loads with digital outputs

Samuel Junglas

Part Number: MSPM0L1304

Hi everyone,

we are currently working with the MSPM0L1306SDYY.

We are about to drive low-gate-charge MOSFETs with digital outputs of the MCU via a 100 Ohm series resistor:

With a gate charge of 0.5nC and a switching frequency of 1.8MHz, the mean sourcing and sinking currents amount to 0.5nC*1.8MHz=900uA lying well inside the current limits given in the datasheet.

However, peak currents will be much higher. As we operate the MCU at 3.3V, with DIO's output impedance neglected, the peak current amounts to 3.3V/100R=33mA.

We have built up a prototype for testing the digital output behavior and the behavior was satisfactory.

Can you tell me whether this kind of connection can cause any damage to the MCU? Are there guidelines from TI for dimensioning these kind of RC-circuits?

FYI: The input capacitance amounts to 50pF.

Best regards

Samuel

over 2 years ago

0 Dennis Lehman over 2 years ago

TI__Guru 70956 points

Hi Samuel,

Let me check with the design engineers on this. Expect a response within 24hrs.

0 Dennis Lehman over 2 years ago in reply to Dennis Lehman

TI__Guru 70956 points

Hi Samuel,

Ok, I'm being told there is likely no concern for long-term damage. The reason is when the GPIO switches high, the top-side FET will act like a voltage controlled resistor and will limit the initial current needed to charge the 50pF load.

I'm double checking with the design simulation team to confirm this. I will keep you advised.

0 Samuel Junglas over 2 years ago in reply to Dennis Lehman

Prodigy 70 points

Hi Dennis,

thank you very much for the reply. Does this mean it could also be possible to completely omitt the 100 Ohm series resistor? If the MCU has an internal current limit, could this be an option. That would make the design even easier for us.

Best regards

Samuel

0 Dennis Lehman over 2 years ago in reply to Samuel Junglas

TI__Guru 70956 points

Hi Samuel,

No. Removing the 100 ohm will cause the peak power to be dissipated in the IO pin, which is what you want to avoid. It is good design practice to have this resistor, so I would recommend keeping it. Our design simulation team does confirm you should be ok with the 100 ohm resistor, but wanted to know what frequency (how often) you turn this MOSFET on and off?