Hi,
I get reply, it is not allowed and VDDA and VREFP are connected to 3.3V, while the digital power supply VBAT_DCDC, VBAT_PMU and VDD are connected to 1.8V for LPC55xx.
This is AE reply:
"
I'm assuming customer wants to use 3.3V VREFP and VDDA for measuring analog voltages greater than 1.8V.
Before we can assess whether the VDDA and VREFP can exceed the VDD/VBAT_PMU/VBAT_DCDC supply voltages, the voltage applied to any IO can not exceed (VDD + 0.5V) as specified by limiting values (DS Table 11). So in theory, the analog voltage shall not exceed 2.3V when VDD is powered using 1.8V supply, no matter whether the ADC part and VREF is powered by 3.3V. Please refer to the pad structure described in the UM11126, figure 49 for ESD clamping diode connections on the IO pad.
Another issue while powering the device with 1.8V: Please note that 1.8V is the absolute minimum voltage for device to functional normally, so powering the device with an 1.8V regulator may exceed the operational range of the device, either transiently or constantly.
Also, there's a note in the pin description which requires VDDA tied to VBAT_PMU/VBAT_DCDC, so the customer's setup is a direct violation of the following requirement described in DS table 3, and since VREFP's maximum voltage is VDDA, so it's not possible using 1.8V to power the VBAT_PMU/VBAT_DCDC/VDD while using 3.3V to power the VDDA and VREFP:
In general, we do not recommend powering the VDDA using a separate power rail on LPC55S69.
"
Hope it can help you
BR
XiangJun Rong
Hi,
I get reply, it is not allowed and VDDA and VREFP are connected to 3.3V, while the digital power supply VBAT_DCDC, VBAT_PMU and VDD are connected to 1.8V for LPC55xx.
This is AE reply:
"
I'm assuming customer wants to use 3.3V VREFP and VDDA for measuring analog voltages greater than 1.8V.
Before we can assess whether the VDDA and VREFP can exceed the VDD/VBAT_PMU/VBAT_DCDC supply voltages, the voltage applied to any IO can not exceed (VDD + 0.5V) as specified by limiting values (DS Table 11). So in theory, the analog voltage shall not exceed 2.3V when VDD is powered using 1.8V supply, no matter whether the ADC part and VREF is powered by 3.3V. Please refer to the pad structure described in the UM11126, figure 49 for ESD clamping diode connections on the IO pad.
Another issue while powering the device with 1.8V: Please note that 1.8V is the absolute minimum voltage for device to functional normally, so powering the device with an 1.8V regulator may exceed the operational range of the device, either transiently or constantly.
Also, there's a note in the pin description which requires VDDA tied to VBAT_PMU/VBAT_DCDC, so the customer's setup is a direct violation of the following requirement described in DS table 3, and since VREFP's maximum voltage is VDDA, so it's not possible using 1.8V to power the VBAT_PMU/VBAT_DCDC/VDD while using 3.3V to power the VDDA and VREFP:
In general, we do not recommend powering the VDDA using a separate power rail on LPC55S69.
"
Hope it can help you
BR
XiangJun Rong
