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regarding EMI fail in Circuit using TLV2734

HY CHO
Prodigy 120 points

Other Parts Discussed in Thread: TLV2374, TLV2371, OPA333

Dear sirs.

Our customer used TLV2734 to sense HV(High Voltage battery) for EV car.

During RI test in EMI, it is exceeded the threshold level in 400MHz~600MHz.

But, they solved this issue by adding capacitor at input terminal.

They want to know as below.

 ☞ Root cause ? (Why is strange about output voltage in 400MHz~600MHz)

☞ What is effect to add capacitor in circuit?

☞ If you have the helpful document to explain it, please share it to me.

Please refer to the attached and then advise me.150521_HV Sensing Circuit_RI test_OPAMP EMI_RI.pptx

  • 0
    TI__Guru* 93105 points

    Hello Hy,

    I believe you have transposed the model number in the title and really intended the TLV2374, as the PowerPoint schematic shows. So my discussion is with regard to this product.

    Many of TI's Precision Analog operational amplifier products have had extensive conducted EMI immunity testing performed. This includes the TLV2374. A report that provides information about the product's EMI Rejection Ratio (EMIRR) vs. frequency is posted on the product web page. It can be found here:

    http://www.ti.com/lit/an/sboz029a/sboz029a.pdf

    The information provided in the Figure 1. graph, TLV2371 EMIRR IN+ vs Frequency, indicates that the EMIRR is very low (~20 dB) in the frequency range of 100 MHz to 1 GHz. Therefore, any RF signal in that frequency range applied to the TLV2374 inputs will see little rejection. Thus, the TLV2374 may respond to the RF in an unexpected manner.

     ☞ Root cause ? (Why is strange about output voltage in 400MHz~600MHz) - The root cause is rectification of the applied RF signal by the input ESD protection cells, or the transistor junctions in the front-end of the operational amplifier. During the time the TLV2374 was being designed there wasn't much awareness how RF could affect the behavior of low frequency, linear amplifiers. That has changed in more recent years and EMI immunity is part of the design consideration. All recent Precision Analog operational amplifiers are characterized for EMIRR and the graph is included in the data sheet, or on the web page. Some operational amplifiers have exceptional EMIRR performance; the OPA333 being one. It has built-in EMI filtering.

    ☞ What is effect to add capacitor in circuit? - The capacitor provides a low impedance path to ground at RF frequencies and essentially shorts the RF out.

    ☞ If you have the helpful document to explain it, please share it to me - See the link to the TLV2371 EMI immunity document. If you need more information, we can find some additional resources.

    Regards, Thomas

    PA - Linear Applications Engineering