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LMH6628QML-SP: Output voltage swing

Alessandro Schirmer
Intellectual 270 points
Part Number: LMH6628QML-SP
Other Parts Discussed in Thread: LMH6628,

Hi,

we use the LMH6628WGFQMLV (5962F0254501VZA) for a space project as video input buffer. Actually we do a radiation analysis and have some troubles with the LMH6628.

In general there is not provided any documentation concerning SEEs (Single Event Effects) by TI.

For the analysis we have to use a worst case transient for SETs according to ECSS-Q-ST-60-15C (if there is no given measurement data from the supplier):

We supply the LMH6628 with -2.5V and +6.8V. This would result into a transient (±VCC) with -2.5V to +6.8V with 15us pulse duration.

We are now wondering if the LMH6628 is able to drive the output pins with VCC. According to datasheet (as we see) the output has to stay 1.2V away from its supply rails.

 

From SNOSAQ1B –DECEMBER 2010–REVISED MAY 2013

Q1: Is the assumption correct, that in case of a SET the output of the LMH6628 is limited to max. VCC-1.2V? Or more general: the output of the LMH6628 is under all conditions limited to a max. voltage of VCC-1.2V (by the internal circuit)?

Q2: Regarding Figure 25 from SNOSAQ1B, is it possible to interpolate the curve for higher loads (e.g. 1kΩ or 2kΩ)? It looks like there is only a small increase for loads greater than 100Ω.

Q3: Regarding the extract from SNOSA02D (industrial grade datasheet): The values differ slightly from the data given in SNOSAQ1B. Is there a real difference between the die of industrial grad and space grade? Or is the information given in the industrial datasheet more generalized for the table of parameters? Is it possible to give a RL=∞ for the space grade LMH6628?

 

With the answers of the above mentioned questions we would be able to adjust our supply levels (lower). So we would be able to still fit the functional input / output range and in case of a SET to drive the lowest transient as possible and to save our subsequent circuit.

 

Thank you.

Best regards, Alessandro

  • 0
    TI__Genius 14211 points

    Hello Alessandro,

    Please find my answers to your questions:

    1. You are correct to a point, at higher supplies you may be able to get closer than 1.2V from the rail.  This is noted in the datasheet snippets you provided.  However in general this headroom value will not change by a large amount even at higher supplies.

    2.  You may extend this curve, but in doing so you are not operating off of strict data.  A spot check at your loads of interest would help you characterize, for your system, what max Vout is at a given RL.  You are correct in that this will trend along a decrease in slope and change little over larger Rloads.

    3. The LMH6628QML-SP is a space-grade version of the LMH6628 industrial-grade.  Package differences, requirements of space applications, and testing methods enable TI to sell a space-grade device, with the ability to continue to perform in radiation-heavy environments.  The industrial grade device is not suited for space applications.

    Best,

    Alec

  • 0
    Intellectual 270 points

    Hi Alec,

    thanks for your reply.

    Concerning Q1: Regarding the output: Is the output limited to VCC-xyVolts? In failure case (SET) is it even possible that the LMH6628 outputs VCC? Or is the device limited to its supply rails with a margin? I assume, that the device is not able to drive VCC at the output.

    Concerning Q3: Is it possible to give a RL=∞ for the space grade LMH6628QML-SP?
    Thanks and Best regards, Alessandro

  • 0 in reply to Alessandro Schirmer
    TI__Genius 14211 points

    Hello Alessandro,

    Q1: You will have headroom limitations and would not be able to achieve VCC due to output swing limitations.

    Q3: Yes, you can use an RL=∞.

    Best,

    Alec

  • 0 in reply to Alec Saebeler
    Intellectual 270 points

    Hi Alec,

    Sorry, my question was poorly worded.

    Q3: Is there an output swing value available for RL=∞ for LMH6628QML-SP (I can't find it in the space datasheet)? Are the output swing values comparable to the values from the industrial grade datasheet?

    Thanks, Alessandro

  • +1 in reply to Alessandro Schirmer
    TI__Genius 14211 points

    Hello Alessandro,

    I understand better now Slight smile.

    Yes, the output swing values are comparable.  Certains specs will have parity from industrial to space-grade, which can be seen in Figure Max Vout vs. RL.  You can view the Max Vout vs. RL curves in either datasheet, and see that for 10V supply and RL = 100 the max Vout would be ~3.65V (Vs = +/-5V, RL=100 are also default test conditions of the rest of the curves, mentioned at the top of each data page).

    If you take this swing to either rail, your Vout_pk-pk would be a little over 7.2V, swinging ~1.35V to either supply.  As you increase RL, you will need to drive less current and will be able to observe some improvement, with diminishing returns, to this headroom spec.

    I hope this helps you evaluate the device, thank you for your good questions.

    Best,
    Alec