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TIDA-01371: TIDA-01371 :The output of the NEGTIVE float_gnd LDO is not stable with cap load.

jia zhang
Prodigy 15 points
Part Number: TIDA-01371
Other Parts Discussed in Thread: OPA140, TLV2171

Hellow TI

1.I design the board refer to the EVM TIDA-01371,  and test single board without the output CAP of the negtive float_ldo very well.

2.But the load of this power board is the TX board of the Untrasound System. There are some decoupling capacitors on the TX board and can't be removed.This make the output of the NEGTIVE float_ldo vibrate.

3.Do you have any suggestions about my problem. It seems that the EVM board  do not suit for real application in Untrasound Hardware System?

4.I think it is the loop problem,can you help to analyze the loop of this TPS7A3301 and the float_gnd.

THX

Follew is my schematic and some test diagram with 330uf cap load. 

  • 0
    TI__Genius 12845 points

    Hello,

    Sorry for the delay. Our system engineer Bill Xu is already discussing this with you offline.

    Regards,

    Sanjay R. Pithadia

  • 0
    TI__Intellectual 870 points

    I review your schematic and compare it with TIDA-01371. below is difference between your design with TIDA-01371.

    1. for error amplifier and sample amplifier, TIDA-01371 use TLV2171. your design use OPA140. the GBP is different for both parts. this may potential reason to cause instable.

    2. TIDA-01371 use single power supply (5V) for error amplifier and sample amplifier. your design use dual power supply(+/- 12V).

    3. there is a typo associate with C190 in your design. According TIDA-01371, C190 should be power supply couple capacitor for Q19 and Q23. but you series a 47ohm resistor.

    4. in TIDA-01371, the LDO output is 3.3V. but in your design, the LDO output is 5V.

    there is still has other differences. could you please update your schematic exactly same with TIDA-01371 and to debug it again? any concerns, let us know.

    regards,

    Bill