About Power block of i.MX28.

[hikaruuruno]

We need some advice about Power block of i.MX28.

We are planning to use DCDC_BATT source only configuration and to make it cheap, the supply voltage be 3.3V for normal operation.

However, since we are also planning to download firmware to NAND flash via MfgTool, the configuration will be 5V source only during download process.

The question is, how do you apply bias to DCDC_BATT and BATTERY during download process if you use the circuit shown in Figure 8 of AN4199?

Will adding another diode next to D1 which is facing the opposite direction work?

Can anyone give us some advice about how to design the Power block?

Or could anyone who made similar board show us the Power block of your schematics, please? We really appreciate it.

The schematic below is our draft.

As you can guess, DCDC_3P3 is derived from a dcdc converter and VBUS is connected to USB0.

VBUS is not supplied usually. And when we use VBUS, dcdc will be disabled.

By the way, are 33uF-capacitor and 0.1ohm resistors really necessary in our case?

Since they take a lot of space, we'd like to minimize the capacitance.

Also, we do not want to use 0.1ohm resictors. If the resistors are to limit the current, can we use, for example, 1ohm instead of 0.1ohm?

Thank you in advance,

Hikaru

[igorpadykov · Accepted solution]

Hi Hikaru

for MFG Tool one needs to provide 5V to VDD5V,

still battery voltage should be applied to DCDC_BATT and BATTERY,

on i.MX28EVK this is BATT_REG derived from 5V

IMX28_EVK_DESIGN_FILES_R10

Best regards

igor

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[hikaruuruno]

Hi Igor,

Thank you for replying.

So in our case, we should not disable the external dcdc but let the dcdc supply 3.3V to DCDC_BATT and BATTERY.

As for the capacitors and resistors connected to VDD4P2, is there any suggestions you can give us?

Thank you,

Hikaru

[igorpadykov]

Hi Hikaru

yes one can enable the external dcdc.

For capacitors please look at i.MX28 EVK schematics.

Best regards

igor