CCS/TMS570LS3137: shutdown power sequence

CHATBOT

Tool/software: Code Composer Studio

Hi my name is Chatbot

I use TMS570L3137 as MPU of our products.
I would like to ask about analog input. Vccad is supplied by TPS65381A, while operational amplifier around the analog input of TMS570 is powered by other 5V source (i.e. isolated DCDC converter).
Regarding start-up sequence, at first TPS65381 starts, and the 5V by DCDC starts. So, there is no over current problem for clamp diode of analog input channel.
While in the shutdown sequence, all the power source is cut off at the same time. But there is short difference between TPS65381 and the 5V generated by DCDC. If TPS65381 shutdown before 5V by DCDC by 10m seconds or less, TMS570 gets permanent damage?

Thanks in advance.

over 6 years ago

0 Sunil Oak over 6 years ago

TI__Mastermind 49120 points

Hello,

Having an ADC input at 5V with VCCAD powered off causes the ADC to be powered by the ADC input. While this may not cause immediate damage the first time, input switches and metallization will be damaged over time with prolonged occurrences.

Regards,

Sunil

0 CHATBOT over 6 years ago

Prodigy 210 points

Thanks for your response ,Sunil-san.

Over voltage on ADC input may not exceeds 10msec in shut down sequence.

If you have any idea, please tell me how are clamp diode or switch damaged in one shut down sequence.

Thanks in advance.

0 Sunil Oak over 6 years ago in reply to CHATBOT

TI__Mastermind 49120 points

Hello,

There are parasitic diodes between each analog input and VCCAD that allow unintentional ADC power up through analog input. I did not mean a single shut-down sequence causing a problem - multiple occurrences of this scenario over time could cause damage.

Regards,

Sunil

0 CHATBOT over 6 years ago in reply to Sunil Oak

Prodigy 210 points

Thanks Sunil-san,

Datasheet of TMS570 doesn't allow input clamp current to exceed 10mA. Do you mean that clamp current could exceed 10mA in a very short period like shutdown sequnece?

Thanks in advance and best regards,

0 Sunil Oak over 6 years ago in reply to CHATBOT

TI__Mastermind 49120 points

10mA is the absolute maximum specification. This value must not be used for normal operating conditions.

Regards,

Sunil

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CCS/TMS570LS3137: shutdown power sequence