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Questions about PMU of i.MX28

Question asked by Hikaru Uruno on Jan 9, 2015
Latest reply on Jan 9, 2015 by igorpadykov

Hello all,

 

Recently we made a custom board with i.MX280 on it which is VDD5V source only configuration.

When 5V is supplied to i.MX280 without any boot devices, VDDIO_3V3, VDDA_1V8 and VDDD becomes likely voltages.

(VDDIO_3V3 : ca. 3.15V / VDDA_1V8 : ca. 1.79V / VDDD : ca. 1.18V)

But VDD4P2 and VDD1P5 become weird value. VDD4P2 becomes ca. 0.8V and VDD1P5 0V.

i.MX280_Power.png

I suppose the voltage of VDD4P2 is not really weird since there is no boot devices and the LinReg is not enabled yet.

But according to the Figure 1 of AN4199, LinRegs of VDD1P5 and VDDD is supplied by LinReg of VDDA.

So if LinReg of VDDD is working, LinReg of VDD1P5 should be working, too.

 

It does not really matter because we do not use 1.5V, but the behavior seems too creepy.

Does anyone know what's going on in the chip, or it causes any problem or not?

 

 

By the way, we are considering to change the configuration to DCDC_BATT source only to reduce the power consumption.

In case of DCDC_BATT source only configuration, can we remove the 33uF capacitor(s) and 0.1ohm resistors connected to VDD4P2? (C5 to C7, C185, C191 and R363, R364 of the evk_revD schematics.)

Since these capacitors and resistors take too much space, we want to remove them.

If we cannot remove these, does anyone can tell us how much watts the 0.1ohm should allow?

We would like to minimize the size of Rs.

 

Thank you in advance,

Hikaru

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