UC3A3 using external 1V8 supply

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#1
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In the EVK1104 circuit I found information about ONREG Flag to switch internal core regulator off.
There is no information in UC3A3 datasheet about this option.
I need an external core supply to decrease my power consumption.

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On the older UC3 MCU's they recommend grounding the input and output of the built-in regulator if you don't use it. There is no enable/disable pin for it, you just feed 1.8v from your external supply to the MCU pins that require 1.8v (ie PLL and Core pins), in stead of from the regulator output pin.

This configuration is not possible on ie EVK1100, you need to design your own board.

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Urgent! big problem :(

I've build my board but there is too much current on vddcore pin something is wrong!?

The two supply voltages (1V8 / 3V0) are generated in my power supply circuit.

Please look at my circuit attached.

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I found Atmel changed AVR32801 document the information about using external power supply was deleted.
In the schematic of avrexplain the L8 pin is shown as ONREG signal.

Someone has an idea?

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can't help, but I'm curious: why don't you use the built in regulator?

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My system battery has 3.7V so it is very important to use an efficient step down regulator because the core needs at full speed 88mA x 1.8V = 158mW. The rest 3.7V -1.8V = 1.9V * 88mA = 167mW is converted to heat by the core regulator.

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Ok.

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I don't see any VDDPLL on your drawing. Also there probably are 2-3 other "core-pins" that must be connected to 1v8.

How many pins are there in total on the chip?

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The chip has total 144 Pins believe no vddpll pin!
This is an AT32UC3A3256-CTUT Chip all pins for 3V3, 1V8, GND are connected. Today I disconnected the vddin pins from GND no changes in power consumption.

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Official statement from Atmel!

I've got confirmation from the designers that the UC3A3 don't support dual power supply. So the datasheet is the correct source. Also the UC3A3 schematics checklist contains correct information on this.

The internal voltage regulators input voltage is specified to be in the range 3.0V - 3.6V, so anything outside is not verified from our side.

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mbruch wrote:
Official statement from Atmel!

I've got confirmation from the designers that the UC3A3 don't support dual power supply.

This is very sad, because using external supply could potentially reduce power consuption to 50%, which in turn reduce battery size to 50% or the device will run twice as long... Also in MCU sleep mode.

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The "LDO" needs 800mV drop down voltage at 100mA (25C°)!
It is save to use 2.65V as supply voltage.
This drops the power loss to 71mW