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OPA376 & OPA377 issue at high temperature

Max Han
Intellectual 2260 points
Other Parts Discussed in Thread: OPA330, OPA377, OPA376, UCD3138, OPA337, OPA378, OPA353, OPA350

 OPA330 is used in Power Brick Module to sample output current from copper at low side. but its GBW is only 350kHz, when at load short test, output current will rise to high because low bandwidth. so customer wants to find a Zero-drift, high GBW ( >1MHz), low offset, Rail to Rail, 3.3V supply, SC70 package OPA.

OPA376, OPA377 and LMV711 are selected and tested. LMV711’s drift is good, but its offset is large.

In this test, the normal output current is 25A, output short current is 50A. current sampling circuit is as attach.

Output current is sampled through Copper, then amplified by OPA376 or OPA377, a RC filter is followed, then ADC of UCD3138 samples the signal and convert it to digital data.

OPA330 is used before, its package is SC70. But its GBW is only 350kHz, from test result in attach excel, we can see it’s react is slow compared with OPA376 and OPA337. So when power module’s output shorts to ground, current protection will be slow, sometimes large short current will damage power module.

In OPA376 and OPA377’s test result, some chips’ output turns down when temperature rising up, curve is as attach, why it can't keep rising up? could you give some explanation for this phenomenon? customer needs it to keep rising up, it can help them to adjust current sample accuracy.

Is this phenomenon caused by our devices or by application circuit?

 How about OPA378? Does it still have this issue?

  • 0
    TI__Guru 60570 points

    Max,

    What do you use to measure OPA376/OPA377 output voltage?  Have you placed a scope at the output to see whether it is stable. With a capacitive load greater than 1uF, OPA376/OPA377 like most op amps is likely oscillating; very few op amps can drive such large capacitive loads - one that can is OPA350/OPA353.

    In addition, you show only partial schematic with no information how you generate GND_RTN?  Is it the same as negative rail?  If you need further assistance, please provide full schematic with clear information regarding supply and input voltage as well as component values used.  Btw, even though OPA376 and OPA377 input common-mode voltage extends to negative rail at 25C, it is not specified over temperature; thus at high ambient temperature and with Vcm=(V-), this may result in much higher Vos drift than max specified value of 2uV/C with Vcm=Vs/2 (mid-supply).