Other Parts Discussed in Thread: TPS53515, , TPS548A20, TPS53915
The TPS53515 is in FCCM when the mode pin is connected to either PGOOD or VREG. What is the minimum voltage requirement for connecting the mode pin to PGOOD?
The MODE pin needs to be pulled up to at least 2.5V nominal for the device to operate in FCCM.
When pulling up the MODE pin to PGOOD, does the resistor need to be exactly the value listed on the datasheet?
The resistors do not need to be an exact match for the MODE pin pullup. For example, a 10k resistor can be used in place of the 20k recommended, so long as the PGOOD pullup voltage is greater than 2.5V.
How can the voltage to the PGOOD pin be supplied?
The PGOOD pin is open-drain, and should be pulled up to a voltage supply. This can by connecting a resistor (eg. 100k) between PGOOD and either VREG or an external voltage. If an external voltage is used, exercise caution when using a voltage less than 3.3V. If the external voltage is less than 3.3V, the voltage seen by the MODE pin may be below the 2.5V threshold, depending on the resistors chosen between the reference voltage, PGOOD, and MODE.
What happens when the MODE pin is pulled up to less than 2.5V?
When the MODE pin is pulled up to less than 2.5V, the part can switch from FCCM to skip-mode. This is shown in the below images. The image on the left shows the MODE pin pulled up to 2.51V, with the TPS53513 switching in FCCM. The image on the right is with the MODE pin pull-up voltage decreased to 2.43V (in reality, 2.45V with a 61k resistor to MODE), and shows that the TPS53515 has transitioned to skip-mode.
What other parts does this guidance apply to?
This guidance also applies to the TPS53513, TPS53515, TPS53915, and TPS548A20 parts.