LMZ31710: Device Not functioning properly after assembly

shivaji magadum

Part Number: LMZ31710

Hi TI,

I am using this buck for 4 different power generation(1.8V, 1.2V, 1.5V, 0.8V). I have trimpot at Vadj to get required vout, RT/CLK is fixed as per the datasheet for each rail . please find attached schematics for one set. After assembled on pcb, each board shows different supply issue. One board show one buck output follows input, Another one has NO VOUT and in some other output not vary at all though we varying Vadj, we checked the Vadj pin is okay. Looked us it could be assembly issue, we replaced the faulty devices, the replaced one worked but nearby buck showing abnormal behavior, this happened with two boards which we sent to assembly house.

Assembly house using temp profile - 241 D.C for soldering. Can some one let me know which is the critical and most sensitive part of LM31710.

schematics for one set:

Thanks.

over 8 years ago

0 J Arrigo over 8 years ago

TI__Mastermind 28020 points

The schematic looks OK. This sounds like an assembly issue.

You mention that after replacing the devices, they all have abnormal operation. Can you share what the abnormal operation is?

You can contact me directly at jarrigo@ti.com for direct support. It would be helpful to see waveforms of the abnormal behavior.

Thanks, Jason

0 shivaji magadum over 8 years ago in reply to J Arrigo

Prodigy 60 points

I have not captured waveforms, checked with multi meter. The behavior is like this - BUCK#1- Vout=Vin, There is no short from input to output but when we give power to buck#1, It gives Vout is same as Vin. BUCK#2 - Vout=0V, PWRGD is High. In BUCK#3 - VADJ resistance variation not effecting on Vout, it always constant, pin shows diode continuity!..

0 J Arrigo over 8 years ago in reply to shivaji magadum

TI__Mastermind 28020 points

After you replaced the devices, did they operate correctly?
It would be helpful to see your reflow profile and solder paste volume. Contact me at jarrigo@ti.com.

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LMZ31710: Device Not functioning properly after assembly