LMH6505: Power sequencing

Nicole Lin

Part Number: LMH6505

Hello,

I am powering an LMH6505 with two LDOs, one which regulates 6V to 5V, and one which regulates -6.5V to -5V. The part is upstream of a differential amplifier that is powered by the same rails. Currently, our power rails are coming up 75ms apart (6V and then -6.5V) which causes only the 5V LDO to regulate correctly while the -5V LDO output is 0V. When the rails are powered by a dual-channel power supply with minimal output delay, the regulators come online just fine.

Does this part have a specification for how much time can elapse between the different rails being powered?

Thanks,

Nicole

over 2 years ago

0 kai klaas69 over 2 years ago

Guru 140200 points

Hi Nicole,

the biggest issue when doing so is to risk latch-up of the regulator which comes up later.

You might want to read this thread with the links given by me there:

https://e2e.ti.com/support/amplifiers-group/amplifiers/f/amplifiers-forum/957524/opa2990-about-powerup-sequence/3539257#3539257

Kai

0 Sima Jalaleddine over 2 years ago

TI__Mastermind 25315 points

Hello Nicole,

That is really good issue to take note of because as Kai mentioned, depending on timing and voltages applied to the device, you may risk general latch-up, overvoltage, and damaging the amplifier. It is best to be safe and avoid the issue by adding TVS diodes to the supply pins. Also, depending on input voltages present at Vin+ and Vin- and before stabilization of the power supplies, you might want to add Schottky diodes at the inputs of the amplifier to the power rails of the device to function as input protection and avoid violating the abs max rating input voltage of the LMH6505.

The thread Kai shared is very helpful, and goes into more detail. The last link on Kai's list: +/- Supply Rail Sequencing and this video on Amplifier EOS starting at 5:25 talks about the importance of these TVS diodes in this type of situation. This thread answered by Kai and Thomas goes into detail on input protection using Schottky diodes.

Thank you,

Sima

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LMH6505: Power sequencing