direct SMPS Hardware design

[khanhcong861989]

Dear all!

this is the first time i design PCB for STM32H755, as my understand for direct SMPS that i design like attach file, really i don't know is it correct, so can you help take look and let me know if any mistake.

[MHoll.2]

Please consult the reference manual (RM0399) chapter 7.4, the Datasheet (DS12919 Rev 2) chapter 6.3.3, and the Application note (AN4938).

1) Inductor in VLXSMPS should be 2.2uH, Isat >= 1.7A, Irms >=1.4A

2) There should be a 220pF Capacitor on Pin VLXSMPS

3) VDDSMPS should have a 4.7uF Capacitor

4) All VDD pins should have a decopling capacitor (normaly 100nF)  and one 4.7uF Capacitor

5) If VBAT is not used it should be connected to VDD

6) 10uH as filter Inductor on VREF, VDDA seems very big

[khanhcong861989]

thanks for yours reply, i modified my design already. 1 question more, i connect VDDLDO, Vcap pin to output of SMPS( Vcore), is it correct. and where should i connect PDR_On pin( to 3.3v or gnd).

[MHoll.2]

Yes if you are using direct SMPS, VCAP has to be connected to the output of the SMPS block:

PDR_ON is set to Vss if You need a running the MCU down to 1.62V, but this will disable the internal PDR supervisor.

If You don't have problems with the Supply voltage then You should connect PDR_ON to Vdd.

[AScha.3]

Hi,

but check in Cube: with direct SMPS the max. core frequency might be lower, because you cannot choose voltage scale setting 00 for core supply, so max. core frequency only possible with LDO or smps+ldo .

So if need max. core frequency use smps+ldo .

[khanhcong861989]

Hi ididn't see the power configuration on STM32CUBE MX, so may i connect VDDLDO and Vcap to out put of of SMPS( Vcore). many thanks all for yours strong support

[AScha.3 · Accepted solution]

>ididn't see the power configuration on STM32CUBE MX

Right, not obvious...see : in RCC -> then in clock tree you see the limit in red, if not allowed high frequ.

Or see in ds -> general op. conditions