Other Parts Discussed in Thread: AM1808, TPS65070
Hi,
The default conenction between the TPS65070 and AM1808 as described in the TPS65070 data sheet and in slva371a.pdf has the 1.8V supply being fed from one of the LDO regulators. In my case, I am using only 3.3V IO with a 5V AC supply. Since the 1.8V also powers the DDR2 memory (not mDDR), I was wondering if it is not possible to supply the 1.8V DDR supply from one of the DC/DC converters to reduce losses and heat generated in the TPS65070. Will the following configuration work:
DCDC3 feeds VDDC (@1.2V-1.3V variable)
LDO2 feeds 1.2V statuc voltages.
DCDC2 feeds 1.8V DDR and USBx_VDDA18
DCDC1 feeds 3.3V to IO banks and all other suppies requiring 3.3V. DCDC1, which is not part of the automatic power-up sequence, is enabled bythe output of DCDC2.
The power-up sequence is still the default: DCDC3 -> LDO2 / DCDC2 -> DCDC1
This fits exactly the sequence shown in the datasheet under 6.3.1. The only potential problem is that the LDO2 and DCDC2 are enabled simultaneously. From the measurements in the slva371a.pdf, it looks as if the LDO output rises much faster than the DCDC output, so the secuence seems to be fine. For power-down, one would just add the little transistor delay circuit on the 3.3V output to reduce the 3.3V rail the moment the 1.8V rail starts to fall - ensuring the that the 3.3V rail never exceeds the 1.8V rail by more than 2V.
This configration feeds all major power consumers from DCDC converters. Does anybody have an opinion as to whether it will work?
Thanks!
Niki
