I have a probrem with"Powering the AM335x With the TPS650250"

zuobing huang

Intellectual 300 points

Other Parts Discussed in Thread: TLVH431

Use of a Clamping Circuit for Simultaneous Ramp Down

When using the ablve Clamping Circuit, because the 1.8V is power on first, the current from the 1.8V to the 3.3V:

(1.8-0.7)/500=2ma。Does the current affect the 3.3V of the CPU?

over 11 years ago

0 Biser Gatchev-XID over 11 years ago

TI__Guru**** 393215 points

I don't understand your concern. Could you explain, maybe post some waveform?

0 zuobing huang over 11 years ago in reply to Biser Gatchev-XID

Intellectual 300 points

The Circuit is a Clamping Circuit for Simultaneous Ramp Down. But when am335x is power up, 1.8V is power first,3.3V is no power( equal to 0V)。So the 1.8V power is run from the TLVH431 and R3 to 3.3V. So the current is ( 1.8-V )/500. V is the positive of the TLVH431 . 500 is R3

0 Biser Gatchev-XID over 11 years ago in reply to zuobing huang

TI__Guru**** 393215 points

I don't see a problem. The voltage on 3.3V rail will follow the 1.8V rail with an 0.7V lower voltage. When the 3.3V rail starts to ramp up it will raise the voltage to 3.3V.

0 zuobing huang over 11 years ago in reply to Biser Gatchev-XID

Intellectual 300 points

According to the excerpt from the AM335x datasheet, the device must be powered on in the following
order:
1. 1.8-V Analog and I/O
2. 3.3-V Analog and I/O
3. 1.1-V Core

"The Voltage on 3.3V rail will follow the 1.8V rail with an 0.7 lower voltage." Is it not a problem?

0 Biser Gatchev-XID over 11 years ago in reply to zuobing huang

TI__Guru**** 393215 points

I don't expect any problem. There will be a problem if 3.3V rises before 1.8V, which is not the case. Anyway the clamping circuit is only needed if you have very small load on the 3.3V rail (tests have been done with 0.01mA load) and it cannot discharge quickly enough during powerdown. Normally the load on 3.3V is quite higher.

0 zuobing huang over 11 years ago in reply to Biser Gatchev-XID

Intellectual 300 points

I understand!

Biser, Thank you very much.

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I have a probrem with"Powering the AM335x With the TPS650250"