Interesting PLL phenomenon in LM4F232

Lubomir Bogdanov1

Other Parts Discussed in Thread: INA198

Hi, guys!

I was doing some measurements and I've noticed that the power consumption of LM4F232 on a EKI-LM4F232 board drops when set to 50 MHz. I've tested it on five boards and go the same results. Take a look see at the graph:

I wonder what causes this?

over 10 years ago

Sue Cozart over 10 years ago

TI__Guru 58650 points

Hi Lubomir,

Above 40 MHz, the Flash speed is reduced to 1/2 the system clock and the prefetch buffer turns on.

Regards,

Sue

Lubomir Bogdanov1 over 10 years ago in reply to Sue Cozart

Intellectual 865 points

Oh, yeah, I never thought of that!

10x

:-)

cb1_mobile over 10 years ago in reply to Sue Cozart

Guru 117850 points

Agree interesting - but also is the wide variation in current demand among your small board assortment. Are all parts of the same revision - and possibly date code? The amount of variation seems outside, "normal/customary."

We note that your results @ 50MHz system clock are just slightly above those @ 25MHz - supporting Sue's analysis. (and likely showing the current burden introduced by that prefetch butter)

Lubomir Bogdanov1 over 10 years ago in reply to cb1_mobile

Intellectual 865 points

HA!

The devices are market with the following:

980 YF
LX4F232H
5QDFIGA3
24A8KYW
G4

and in the datasheet I saw the following:

"An X, for example, LX4F232H5QDFIGA0, indicates the
part is experimental and requires a waiver"

which might explain the big variation. Besides don't forget the differential amp INA198, connected to the supply, which also has an initial offset...

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Interesting PLL phenomenon in LM4F232