st10f269 reset at low vdd

yadagiri · ‎2003-06-23

Posted on June 23, 2003 at 11:55

yadagiri · ‎2003-06-18

Posted on June 18, 2003 at 10:30

Hi,

I am analyzing a circuit built around st10f269 mico. I would like to know the absolute minimum voltages required for the micro to function. As I understand it needs 3.3v for internal logic to function correctly and all external logic functions at 5v. I am facing a problem during power up phase. When the supply voltage is around 2V, I am getting a 500mV reset pulse at reset in pin. I would like some one share his/her knowledge regarding the behaviour of micro during powerup phase.

Thanks

maxime2399 · ‎2003-06-18

Posted on June 18, 2003 at 11:17

The ST10 require to be forced in reset mode by an external reset circuit during power-up in order to work properly.

It require 5V +/-10%. The 3.3V is generated internally from the 5V.

The ST10 has several mode of reset I descrided in another thread for the 172/272:

http://www.stmcu.com/forums-cat-87-5.html

yadagiri · ‎2003-06-18

Posted on June 19, 2003 at 06:46

Hi MAX,

Thanks for your reply. You are absolutely correct. My problem is we are using Infineon 4270 regulator IC to generate +5V regulated voltage and a delayed reset. But during simulation I observed that when the system is powered-On, the regulator output starts to increase from zero to 5V, ideally the reset signal should be low during this time till the delay time, but I found that the reset signal instead of being low it increases with the output voltage and the it becomes low. the max peak I found was around 350 mV at normal temperature and 650 mV at 125 deg cent. What I was interested is that does this reset pulse behaviour cause any malfunction of the circuit. The regulator output at 350mV reset peak is around 1.5-2V. Does the micro work at this voltage? About the regulator behaviour I got confirmation from the Infineon about the reset behaviour. I want any one of your if faced such a situation how you solved it.

Thanks

maxime2399 · ‎2003-06-23

Posted on June 23, 2003 at 11:55

You are asking here a difficult question!

we cannot say for sure that the ST10 will not start working with a 1.5-2V supply, even so we cannot say for sure it will work.

It's even worse some parts may work, some not and some may work partially and all this is function of the temperature.

Therefore there is a risk here that the device starts showing some activity until the real reset happens.

When the reset pulse happens, it will bring the device in a know state and the application will start running correctly.

In order to avoid any strange behaviour during the start-up, I recommend to add pull-ups and pull-downs on all the critical I/Os. I recommend also to avoid to put cricical signals on the memory bus, more likely to start toggling in case of random system set-up.

You may want to pull down the reset pin to see if it improves the behaviour of your reset circuit.

You may want to have a look at other reset/regulator combination circuit on the market ( ST for example...)

Even so they may have a similar behavior, the maximum voltage level may be lower

There is other parameters very important to evaluate the reset phenomenon, like the maximum rising time of the power supply or the clock source.

For example if the pulse on the reset pin is short enough, the quartz oscillator will not have time to start, therefore the ST10 won't be doing anything armfull...