MC33907 pin 37

[matej_15]

Hi!

We are using MC33907LAE. Can you please tell us the purpose and current requirements of pin no. 37 - "VPRE". Is it a signal feedback input for the VPRE regulator or power input for other LDOs or something else? We are asking so that we know how to route it, as a thin sensitive trace or as a wide power trace. Maybe there is some documentation reference to that pin?

Br,

[TomasVaverka]

Hi Matej,

VPRE is the output pin of the SMPS pre-regulator, delivers a typical output voltage of 6.5 V which is used mainly internally.

Some general recommendations for PCB layout can be found in Section 8 of the AN4766.

Best regards,

Tomas

[matej_15]

Hi @TomasVaverka ,

can you please explain this a little bit? How can pin no. 37 "VPRE" be an output?

Since this is a SMPS with switching node on pins SW_PRE1 and SW_PRE2 ? Thank you.

Br,

[giraffe508 · Accepted solution]

You are correct that pin no. 37 'VPRE' is not an output. It is actually an input pin for the SMPS pre-regulator. The VPRE pin is used to provide an external voltage to the pre-regulator, which is then used to power the internal circuitry of the MC33907LAE.

As for the switching node, you are correct that the switching node is on pins SW_PRE1 and SW_PRE2. The VPRE pin is not directly related to the switching node, but it is used to provide an input voltage for the pre-regulator, which then generates the required internal voltages for the device.

For more information on the MC33907LAE and its pin functions, you can refer to the MC33907/08 Data Sheet.

Best regards,

[matej_15]

Hi @TomasVaverka, any news on this topic?

Br,

[TomasVaverka]

Hi Matej,

I am not sure what else you need to know, once again the Vpre voltage pre-regulator with an integrated high side switching MOSFET is a flexible switched-mode power supply (SMPS) which can be configured in two topologies: Non-inverting buck-boost or standard buck depending of the external configuration. The configuration is detected automatically during start-up sequence – see DS for more information. The output voltage Vpre is regulated in the ranges which depend on the VSUP voltage and used mode of pre-regulator, see the figure below. The output current capability is up to 2 A. The SMPS pre-regulator also keeps power dissipation down and eliminates the need for bulky heat sinks compared to linear regulators.

Best regards,

Tomas

[matej_15]

Hi @TomasVaverka,

the confusion came from your initial answer where you've stated that "VPRE is the output pin of the SMPS pre-regulator". I wanted to clear that one up since it doesn't make sense that VPRE pin is an output.

Answer from @giraffe508 cleared everything:

You are correct that pin no. 37 'VPRE' is not an output. It is actually an input pin for the SMPS pre-regulator. The VPRE pin is used to provide an external voltage to the pre-regulator, which is then used to power the internal circuitry of the MC33907LAE.

As for the switching node, you are correct that the switching node is on pins SW_PRE1 and SW_PRE2. The VPRE pin is not directly related to the switching node, but it is used to provide an input voltage for the pre-regulator, which then generates the required internal voltages for the device.

For more information on the MC33907LAE and its pin functions, you can refer to the MC33907/08 Data Sheet.

Best regards,

@TomasVaverka can you please confirm this?

Br,