Video amplifier for DM814x and AM387x

YILMAZ KIRÇİÇEK

Intellectual 905 points

Other Parts Discussed in Thread: OPA361

Hi all,

I want to use an external video dac amplifier instead of internal ones.

Datasheet referencing TRM but there is no any relevant information on TRM.

There is only a gain information (3.7V/V) on Figure 42. (pg. 272)

Could you please supply us related documentation or directly suggest appropriate video amplifier.

(I prefer dual channel amplifier with intertanal reconstruction filter.)

Best regards.

For additional Video DAC Design guidelines, see the High Definition Video Processing Subsystem chapter of the TMS320DM814x DaVinci Digital Media Processors Technical Reference Manual (Literature Number: SPRUGZ8).

over 12 years ago

0 Biser Gatchev-XID over 12 years ago

TI__Guru**** 393215 points

Hi Yilmaz,

Here is a quote from another post:

"TV_OUT (Pin AH24) is typically used for direct drive of a video load without an external amplifier. When an external amplifer is used in bypass mode, TV_VFB (PIN AG23) is required. When operating in bypass mode, the DAC will source current into a load resistor (R-load). With the full-scale curent (470uA) and R-load (1500 ohms) specified in the DM for bypass mode, gain of 3.7V/V should provide a 1.3V video range after video termination (470uA x 1500 x 3.7 / 2) . If 5.2V/V gain (e.g. OPA361) is used instead of 3.7V/V, R-load at the DAC output could be reduced to 1070 ohms to provide the same 1.3V video range."

Hope this helps you.

Best Regards

Biser

0 YILMAZ KIRÇİÇEK over 12 years ago in reply to Biser Gatchev-XID

Intellectual 905 points

Hi Biser,

I thank you very much for sharing your experience and time with us.

But according to datasheet Rload is limited beetwen 1485 to 1515 Ohms.

And also there is 500 Ohm load resistor in input of OPA361. (adding parallel resistor is not recommended according to advices on this forum because of tolarance issues.)

So I am evaluation use of a G=1 amplifier (with integrated reconstruction filter) after internal amplifier. But could not able select appropriate amplifier.

Could you please advice more appropriate solution if it possible.

Best regards.

0 Biser Gatchev-XID over 12 years ago in reply to YILMAZ KIRÇİÇEK

TI__Guru**** 393215 points

Hi Yilmaz,

The comments above that I sent you are quoted from a TI expert. The load resistor values in Table 8-42 are valid for a 3.7V/V amplifier. If you choose a different gain amplifier, the necessary calculations as given above are valid.

0 YILMAZ KIRÇİÇEK over 12 years ago in reply to Biser Gatchev-XID

Intellectual 905 points

Hi Biser,

Thank you for your answers and clarifications.

OPA361 has 500 ohm load resistor and gain is 5.2

So 470uA x 500 x 5.2 / 2 gives 611mV.

Could you please help me, how to implement DM8148 video amplifier with OPA361.

Best Regards.

0 Biser Gatchev-XID over 12 years ago in reply to YILMAZ KIRÇİÇEK

TI__Guru**** 393215 points

Hi Yilmaz,

You are right, I forgot that the OPA361 has an internal 500Ohm load resistor. Here is a link to TI's range of video amplifiers:

http://www.ti.com/paramsearch/docs/parametricsearch.tsp?family=analog&familyId=1476&uiTemplateId=NODE_STRY_PGE_T

You will certainly find one that suits your design.

0 YILMAZ KIRÇİÇEK over 12 years ago in reply to Biser Gatchev-XID

Intellectual 905 points

Hi Biser,

I have already checked out all TI video amplifier with integrated reconstruction filter before asking the forum, but could not find an appropriate one.

I would be appreciated if you offer one.

Best regards.

0 Biser Gatchev-XID over 12 years ago in reply to YILMAZ KIRÇİÇEK

TI__Guru**** 393215 points

Hi Yilmaz,

There is a separate forum, dedicated to amplifiers: http://e2e.ti.com/support/amplifiers/default.aspx. I'm sure their experts can help you better with your choice.

0 YILMAZ KIRÇİÇEK over 12 years ago in reply to Biser Gatchev-XID

Intellectual 905 points

Thanks for all Biser,

I am heading to Amplifier Forum.

Best regards.

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Video amplifier for DM814x and AM387x