THS4513EVM: EVM mechanical drawing

Hey Tim,

Looking into this and will get back to you.

Best,

Hasan Babiker

Hello Hasan,

I'd much appreciate getting the mechanical drawing as soon as possible. However, i think the EVM we need to use is THS4508EVM.

We need to build (very quickly) a DC-coupled adapter for one of our products (AXS83823 DAQ), which uses the TI ADS54RF63 ADC. Previous applications have always been AC-coupled, and frequency based, but we have an important customer who requires DC coupling.

(We're over a month late delivering the product, and the DC-coupling requirement arose only a week ago...)

The ADS54RF63 datasheet gives a recommended front-end interface circuit to support DC coupling (p. 27-28 of datasheet). The circuit calls out a THS4509, with the CM pin connected to the VREF pin of the ADC through 50 ohms. The ADC VREF pin has a nominal level of 2.4V. But the THS4509 has an input range between -1.5V and +1.5V.  The CM bias current of the THS4509 is +/- 40uA (1.25V through 3.5V; see question below), so it would appear that the CM pin is being driven outside of its recommended range.

HOWEVER, THS4508 has an input range of 1.25V through 3.75V. So, I'm concluding that it is a better part choice for the DC coupling circuit.

I admit to considerable confusion regarding the CM voltage ranges of the amplifier series THS4508, 4509, 4511, and 4513.  I suspect a possible error in the '4509 datasheet: The other three parts in this series specify the CM pin bias current within the min/max CM pin voltage ranges. But for the THS4509 the bias current is spec'ed well outside the voltage range of -1.5V through +1.5V.

So, I'm asking for two things:

1. Clarification on the best part to use in the DC coupling circuit (which I think to be THS4508).

2. Mechanical drawings for ALL FOUR EVMs: THS4508EVM, THS4509EVM, THS4511EVM, and THS4513EVM.  I suspect that the mechanicals are same, but since we're not quite sure which one we'll be using I'd like to design for ALL FOUR options.

I've attached a document showing the DC-coupling circuit (Fig. 51 from the ADS54RF63 datasheet) as well as the CM specs of all four amplifiers in the series. (Or at least I've tried to attach it. All I see, though is a large icon.)

Thank you!!

Best regards,

Noble Larson

Hardware design engineer

Axsun Technologies - Division of Excelitas

Billerica, MA

DC coupling ADS54RF63 analog inputs.doc

Hello Noble,

I think the confusion lies in how the THS4509 is being supplied in the ADS54RF63 datasheet vs the THS4509 datasheet. Notice that in the ADC datasheet the part is in a single-supply configuration, where VS+ = 5V and VS- = 0V. However, in the THS4509 datasheet the test condition is being set at Vs+ = 2.5V and Vs- = -2.5V. The "maximum output voltage" high and low spec that you are looking at is in reference to the mid-supply of the part. So in actuality if you were to use the THS4509 in a single supply configuration, it's max/min output voltages would be:

Maximum output voltage high = Mid-supply + 1.4V = 2.5V + 1.4V = 3.9V

Minimum output voltage low = Mid-supply - 1.4 = 2.5V - 1.4V = 1.1V

You will see that the THS4508 is already being tested in a single-supply configuration in its datasheet, and that is the reason you get the 3.8V and 1.2V values. So in summary the THS4509 actually has a larger output range than the THS4508, the issue lies in that their datasheet is specd at different conditions. Neither of these parts would be driven outside of their recommended range when using the ADS54RF63.

Hope this clears things up, I will try to provide the mechanical information as soon as I can.

Best, 

Hasan Babiker

Hello Hasan,

Thanks for the extremely clear answer to my question. I had missed the fact the the voltage rail test conditions are very different in the two specs.

Our output voltage range is +1.85V to +2.95V, which appears to be well within the specs of both parts. The THS4508, though, may be better for our application, as our customer may want to operate at unity gain. In any case, I'm ordering both EVMs, for testing.

Best regards,

Noble

Hello Hasan,

I got myself confused regarding the min gains of the four amplifiers. (As you no doubt know) it's THS4511 and THS4513 which can operate at unity gain, whereas my attachment had things mixed up a little.

So, (as I mentioned last week) I will need the mechanical drawings of all four EVMs, so that my carrier board can (hopefully) accommodate all of them.

Just one clarifying question: All four amps can operate in a single supply mode (Vs+ = 5V; Vs- = GND), right?

Thanks again,

Best,

Noble

Hi Hasan,

Sorry to bombard you with questions, but I have another one:

THS4508 and THS4509, as discussed previously, both must operate at min gain of 6dB (2X).  But, we should still be able to achieve net unity gain by configuring the outputs as shown in Fig. 44 of the THS4508 datasheet. There, the differential outputs pass through 50 ohm resistors, which, combined with a 100 ohm load, result in a 6dB attenuation across the load. So, the net gain should be unity.  Is this correct?  (Sorry for the elementary questions, but it's been quite a few years since I've designed with op amps, and we're on a tight schedule, with little time to "get back up to speed" on the subject.)

Our customer might even prefer 6dB gain, but I'd like to support net unity gain, if possible.

Thanks again!

Regards,

Noble

Hello Noble,

Both your assumptions are correct. All of the amplifiers should be able to be run in a single-supply configuration. Also using the THS4508 or THS4509 in the manner you described (at a gain of 2 with -6dB attenuation at the output) will give you the unity gain you are looking for.

Best,

Hasan Babiker

Hello Hasan,

I think I've gotten/found answers to my technical questions about the amplifiers.

What I really need now are the mechanical drawings for the boards: at least: 

THS4508EVM and THS4509EVM

(I've concluded that we'll have to operate the amp with a gain of at least 2, and we probably won't need to use the 4511 or 4513.)

Aside from hole positions, I'd like to know the drill dimension for the three TPs. I know the installed part is Keystone 5000, with a recommended drill size of 0.040", but it would be nice to see this on a drawing.

Thank you.

Regards,

Noble

Hello Noble,

Both the THS4508 & THS4509 EVMs should have the same board dimensions of 1.665 in x 3.96 in. I've attached the drawings of each board, the hole information (same for both boards) and the step file for each board.

E2E THS450X.zip

Best,

Hasan Babiker

Hello Noble,

I see you have rejected my latest reply. Is there any more information you need for your design?

Best,

Hasan Babiker

Hello Hasan,

I did, indeed, receive the zip file with the mechanical info for the two EVMs.  Thank you!

I certainly didn't intentionally reject your reply, but it might have happened inadvertently due to the recent migration of our email, OneDrive and most everything else over to the system of the company that recently acquired us. (I've also been out of the office today, helping a fried get her off-grid water supply system - well/pump etc. - diagnosed, consequent to total breakdown - i.e. no water in the house...)

Anyway, the info you sent looks good, and should suffice for me to finish the layout of my "carrier" board for the EVM(s).

Meanwhile, I've been delving into the mysteries of fully differential amplifier gain, input termination, etc. (Ti app note SLOA05E on same).  I think I'll soon know more about differential amps (and rural water supply systems) than I ever wanted to know.

Many thanks for your help.

Best regards,

Noble