MSPM0L2116: Please help confirm whether an external resistor is in fact required for the MSPM0L2116 SYSOSC

Part Number: MSPM0L2116

Team,

From our customer using MSPM0L2116SPMR:

Regarding the MSPM0L2116 hardware design, I noticed several requirements in the design guide and have two questions. Could you please help double-check and confirm them?

1. ROSC: I cannot find this pin in the MSPM0L2116 datasheet. I am not sure whether the MSPM0L2116 SYSOSC uses an internal calibration resistor or requires an external calibration resistor. Could you please help confirm whether an external resistor is needed for the MSPM0L2116?

2. VREF+ and VREF-: Since we will be using the internal reference, can these two pins be assigned to other functions, such as LCD driver outputs?

[TI REPLY - email thus far]

So based mostly on the specific MSPM0L2116 technical documentation, here are some responses to your design questions:

1. ROSC and SYSOSC Calibration

The ROSC pin is indeed associated with the SYSOSC (System Oscillator) frequency correction loop (FCL).

• Is an external resistor needed? It depends on the specific device configuration and required accuracy. The documentation states that the SYSOSC frequency accuracy can be improved using the FCL feature, which can use either an internal resistor or an external resistor (connected between the ROSC pin and VSS).
• Confirmation:  However, we must check the device-specific datasheet for the MSPM0L2116 to see if your specific part supports "Internal Mode," "External Mode," or both.
  • If the device supports Internal Mode, you do not need an external resistor.
  • If you require higher precision or if the specific device variant only supports External Mode, you will need to populate an external resistor on the ROSC pin.
  • I’m having trouble ascertaining this directly from the device DS [SETUSEEXRES bit] and may need to clarify with the product team.  It appears to me it may require the external resistor (is this okay?).  For a high-precision board anyway, it is often common practice to include the ROSC resistor pad on your PCB layout even if you intend to use the internal mode. This "future-proofs" your design in case your application requires higher stability than the internal resistor can provide
  • But you could (if possible) try to look for this yourself with the following in your code:

2. VREF+ and VREF- Pin Assignment

Regarding the use of these pins for other functions like an LCD driver:

• Internal Reference Usage: If you are using the internal reference (the 1.4V or 2.5V user-selectable internal sources), the VREF+ and VREF- pins are available for other purposes.
• Pin Multiplexing: According to the Pin Attribute Tables, the VREF+ and VREF- pins are multiplexed with other functions. For example, in some packages, VREF+ is multiplexed with LCD_LCD25.
• Recommendation: You can assign these pins to other functions (such as LCD driver outputs), provided that:
  1. The internal voltage reference is correctly configured in software.
  2. The specific pin you choose for the LCD driver is not required to be the VREF+ or VREF- pin for an external reference (which you've stated you are not using).
  3. You verify the specific pin mapping for your package (e.g., PM, DGS28, etc.) in the Pin Attributes table of the datasheet to ensure there are no conflicts with your intended LCD segment/common pins.

Let me know if this helps.  I could initiate a quick e2e post on trying to confirm the external or internal resistor – just let me know if you prefer one over the other first.  (If you don’t mind the external, we’re good to go)

TY,
CY