LPC55S28 VBAT_DCDC ramp vs VDD

[riversandrobots]

Hello,

I have a few questions regarding the LPC55S28 controllers and the VBAT_DCDC ramp rate vs the timing with the VDD power on sequence. I see in the errata (and latest datasheet) that there needs to be a ramp rate of 2.6ms or greater for VBAT_DCDC.

1. Does the VDD need to also exhibit this timing upon power up?

2. Can the VBAT_DCDC voltage come on later than the VDD power?

3. For the VBAT_DCDC, does this need to be a true ramp, or can it just have a time delay, then have a faster rising on point?

[xiangjun_rong]

Hi,

1.Does the VDD need to also exhibit this timing upon power up?

>>>The VDD power supply just provides power for the I/O cell, there is not requirement to the VDD timing during power-up.

2. Can the VBAT_DCDC voltage come on later than the VDD power?

>>>>Generally, you can connect the VBAT_DCDC and VDD and VDDA together, if you power VDD separately, I suppose that the VBAT_DCDC voltage should be early than VDD.

3. For the VBAT_DCDC, does this need to be a true ramp, or can it just have a time delay, then have a faster rising on point?

>>>>>The VBAT_DCDC requires a true ramp based on ambient temperature

Hope it can help you

BR

XiangJun Rong