MSP430F6746: Questions for device power up

Hi Koichiro,

Koichiro Tashiro said:

Q1) Is there any power up slew rate limit?

It is described in datasheet: 1000V/s.

Koichiro Tashiro said:

Q2) When the power was turned on, the reset signal to the device was High. Is this a problem?

It is correct that RST signal is high.When this pin is configured as reset and it is low voltage, then reset is asserted.

B.R.

Sal

Hi Sal,

For Q2), the customer is asking if RST pin is high during power-up, it leads to the high current (2A) and device crash.

Sal Ye said:

When this pin is configured as reset and it is low voltage, then reset is asserted.

Above your comment means even RST pin is high, the device is internally kept reset state during power-up until DVCC is over V(DVCC_BOR_IT+).
So it should be no problem, correct?

Thanks and regads,
Koichiro Tashiro

Hi Koichiro,

Yes, when RST is high, then it has no effect on internal reset state.

However, we do NOT recommend that voltage of RST is higher than DVCC, because it described in datasheet:

Always set the voltage source of RST and DVCC same, so it won't happen what you descibed. Here is the recommened hardware design: https://www.ti.com/lit/pdf/slau278 (Chapter 2.1)

Koichiro Tashiro said:

When the power supply is turned on, the device drew more than 2A and the device was broken.

Please check whether there will be some short connection of the board. Or overspec of voltage supply, why not grab a waveform of power supply voltage? It shouldn't be relevant to RST voltage.

B.R.

Sal

Hi Sal,

Regarding Q2, I confirmed "RST=High" means connected to DVCC. So RST is not higher than DVCC. So it is not problem.

For Q1, the customer wonders 1000V/s is real max spec.
The table you pointed out also shows the test condition with 10mV/us = 10000/V which is bigger than 1000V/s.


In case, DVCC is 3.3V, what is the minimum rise time?
a) 3.3[V] / 1000 [V/s] = 3.3ms
or
b) 3.3[V] / 10 [mV/us] = 0.33ms

Thanks and regards,
Koichiro Tashiro

Hi Koichiro,

Actually, you make it clear that it is a test condition, so it is not a recommended operation range. It means at the specific condition, the delay time of after SVSH turned on.

Please refer to 1000V/s = 1mV/us.

B.R.

Sal

Koichiro:

About the 2 Ampere draw during the power up, and then a broken device, I have one comment. If you have many IOs which are acting as drivers or sensors, assure that their interface circuits create a long enough time delay so the MSP430 can power up before the IOs rise to full power. Letting the IO interface circuits rise to full power before DVCC reaches full power could break the MSP430.

Hi Sal,

I see. I understood 1000V/s is recommended operation range.
What is absolute maximum range?

Thanks and regards,
Koichiro Tashiro

Hi Thomas,

Let me check with the customer about their IO usage.

Thanks and regards,
Koichiro Tashiro

Hi Koichiro,

It is the maximum range, because it is listed with max value.

Over the range may do harm to device. It will not immediately occur, but have risk.

B.R.

Sal

Koichiro:

We see that 2 Amperes is far too high of a draw for the MSP430. Please provide us with a schematic that shows all the interface circuits between the MSP430 and the external power supply and peripheral devices. I think that is a proper place to begin to solve your problem.