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DRV8305-Q1: datasheet spec clarification

Viktorija Cecil
Mastermind 18491 points
Part Number: DRV8305-Q1

Team, 

Help answer my customer's questions below, please:

Can you help me please with some clarification on datasheet parameters for the Current Sense Amp of the DRV8305NE (…PHPRQ1)? References are specifically to “SLVSD12C –MAY 2015–REVISED SEPTEMBER 2017” datasheet – primarily page 10.

  1. Is GERR the tolerance for GCSA? If not, what is GERR relative to as a %?
  2. UGB is stated as 2MHz typical at GCSA=10. UGB generally means unity gain bandwidth, so does this mean that at the gain setting of 10V/V the bandwidth is 200kHz? Or is does this parameter mean the bandwidth at GCSA=10 is 2MHz (i.e. unity gain BW = 20MHz)?
  3. How does bandwidth vary with temperature? Is it monotonically decreasing with temperature? Increasing with temperature? Other? Having only a typical, am I to infer that the it flat with temperature?
  4. How does bandwidth vary with PVDD? Flat within the specified 4.4 to 45v range?

 Thanks!

Viktorija

  • 0
    TI__Intellectual 2595 points

    Hi Viktorija,

    1) Yes, GERR is the tolerance for GCSA.
    2) At 10V/V the bandwidth is 200kHz. GCSA = 10 is just specifying the test condition used to determine this spec, since the device does not have a 1x gain mode the 2MHz UGB is back-calculated from the gain bandwidth product at 10 gain. Correction: At 10V/V bandwidth is 2MHz. The implied unity gain bandwidth is 20MHz.
    3) Bandwidth will typically decrease with temperature.
    4) The CSAs are supplied from AVDD, so CSA operation should not be affected from PVDD = 5.3 to 45. Below 5.3V, AVDD will start to drop out (about 0.4V below PVDD), so this can affect bandwidth slightly.

    Thanks,
    Garrett

  • 0 in reply to Garrett Walker
    TI__Mastermind 18491 points

    Garrett,

    From customer:

    I understand that gain falls off proportionally with frequency and that one can test at a different gain and infer the UNITY gain BW.  I was hoping you would tell me that the datasheet was a misprint and that the value represented the BW at gain of 10 (i.e. tru UGB = 20MHz).  I’m VERY surprised by your response that the amp effectively has typical BW=200kHz at gain of 10.

    At room temp I am seeing MUCH MUCH higher BW than the spec would indicate. The pic below imply that the BW of the amp is >10MHz at gain of 10.

    1. Yellow – is across sense resistor (input to amp)

    2. Green – is the amp output (gain=10)

    3. Blue – is after the filter we placed on the output. (the first pic is with 1MHz filter, the second is with 10MHz filter)

    Can you double check that the unity gain isn’t misstated in the datasheet? Honestly, gain of 200kHz at gain of 10 would present severe difficulties for us. With 200kHz BW at gain of 10, the output of the amp will distort the pulse 5x worse than the blue pulse of the first picture.  

    Thanks

    Viktorija

  • 0 in reply to Viktorija Cecil
    TI__Intellectual 2595 points

    Hi Viktorija,

    After further investigation, it appears this spec was originally intended to be the gain-bandwidth at gain = 10, not the unity gain bandwidth product. As such, the bandwidth  for the various settings should be:

    Gain = 10 : BW = 2MHz
    Gain = 20 : BW = 1MHz
    Gain = 40 : BW = 0.5MHz
    Gain = 80 : BW = 0.25MHz

    Thanks,
    Garrett