| Richard Erlacher 03/18/12 13:15 Read: 171 times Denver, Co USA Msg Score: 0 +1 Good Answer/Helpful -1 Overrated |
#186774 - Nothing. has been proven yet. Responding to: Erik Malund's previous message |
Erik Malund said:
<ui>Adding more capacitance between logic power and gnd will increase the rise and fall time of Vcc with respect to Gnd,
I know that you, with your supervisor chip avoidance, have a fixation with that I, like most others, DO NOT!!! Erik I don't know what you mean. I've experimented with supervisors of various sorts. I've also experimented with various sorts of regulators and power sources. I've found that, in my own experience, those brownout bugaboos relating to program-store-content-loss that trouble the 805x community at large, don't make themselves apparent when the Vcc supply rise and fall times are very short. I don't deny that there are other brownout-related problems, but just hitting the RESET doesn't always solve those problems. Since there are different levels at which various devices perceive "out-of-spec" Vcc, the behaviors of MCU's, supervisors, BBRAM's, and other devices can be very hard to predict as Vcc wanders around the 4.5-volt level. Some devices will respond as though it's a brownout, while others will not. They don't all have the same hysteresis, either. I know the Dallas BBRAM's that I was using when I first encountered some of these anomalies don't behave in the same way as the Dallas MCU's built-in brownout detector does. Additionally, I've observed that supervisors do absolutely nothing useful during the power-down transient, aside from activating the RESET. My argument is, once again, that nothing guarantees what happens when RESET is active but Vcc is below the acceptable level. Additionally, as I've pointed out, not all devices have a RESET input. Many people think that a large capacitor will compensate for an under-specified raw input to the on-board regulator. Some think that additional capacitance on the output of their on-board regulator will solve the too-weak-input problem. I am not among them. Designing with a 20% margin of safety ijnto the raw input supply might be cheaper in the long run than adding extra Vcc-to-Gnd capacitance, and it causes no increase in Vcc rise and fall times. While I'm forced by circumstance to respect the general opinion that a supervisor will, in general, make these problems "go away," I know that nobody has made the assertion that they've spent any time testing that notion. Consequntly it's just an unproven hypothesis. I'm still convinced that the guys at Intel couldn't get their oscillator to start reliably, so they used a RESET time-constant long enough to convince their boss that it would start most of the time, rather than figuring out how to do it properly. The FLASH-corruption issue didn't come about until FLASH-based program store became a reality. This makes the supervisor look more like a fig-leaf rather than a solution. Maybe someone with a real motivation will actually spend the time and resources to perform rigorous testing on the function of the supervisor in this environment rather than allowing it to continue to float in the fog. RE |
| Topic | Author | Date |
| Sine wave detection on microcontroller | Yagnesh Mehta | 03/07/12 04:59 |
| Detect or measure? | Per Westermark | 03/07/12 05:25 |
| not detection, measurement of sine wave signal | Yagnesh Mehta | 03/07/12 06:14 |
| What are you measuring? | Andy Peters | 03/07/12 10:05 |
| RMS and Average - 1st Priority | Yagnesh Mehta | 03/07/12 20:59 |
| 415 v | Mahmood Elnasser | 03/08/12 22:07 |
| I have to do using MCU | Yagnesh Mehta | 03/08/12 22:48 |
| Start simple | Mahmood Elnasser | 03/08/12 23:17 |
| if time is major isssue than..... | Yagnesh Mehta | 03/08/12 23:31 |
| People responding to specific questions | Per Westermark | 03/09/12 02:14 |
| Same Technique.... | Yagnesh Mehta | 03/09/12 04:32 |
| RMS | Maarten Brock | 03/09/12 05:49 |
Sorry for my laziness  | Yagnesh Mehta | 03/09/12 20:50 |
| So what have you done? | Per Westermark | 03/09/12 06:19 |
| Require more work... | Yagnesh Mehta | 03/10/12 00:50 |
| Working on that | Yagnesh Mehta | 03/10/12 06:12 |
| options, options | Per Westermark | 03/10/12 06:49 |
| Help me | Yagnesh Mehta | 03/08/12 21:31 |
| Okay | Joseph Hebert | 03/09/12 06:13 |
| Are many threads available | Per Westermark | 03/09/12 06:29 |
| when you save a char ... | Erik Malund | 03/09/12 08:09 |
| Why don't you specify your problem COMPLETELY? | Richard Erlacher | 03/09/12 11:36 |
| Already specify it | Yagnesh Mehta | 03/10/12 02:07 |
| there are some details? | Richard Erlacher | 03/10/12 07:51 |
| comparisions | Yagnesh Mehta | 03/12/12 01:16 |
| How are you calculating your needed sample rate? | Per Westermark | 03/12/12 01:54 |
| start with simple one.... | Yagnesh Mehta | 03/12/12 08:02 |
| You do know sin(90+angle)? Or 2-log computations? | Per Westermark | 03/12/12 08:48 |
| ADC resolution............ | Yagnesh Mehta | 03/12/12 12:27 |
| impossible or wrong | Erik Malund | 03/12/12 13:30 |
| double post, ignore | Erik Malund | 03/12/12 13:30 |
| Precision Rectify: | Erik Malund | 03/12/12 06:44 |
| SCR Chopped Wave | Yagnesh Mehta | 03/12/12 07:48 |
| What accuracy do you need? | Kalpak Dabir | 03/12/12 08:43 |
| CT accuracy | Yagnesh Mehta | 03/12/12 12:58 |
| the fundamental | Erik Malund | 03/12/12 13:41 |
| 50Hz | Per Westermark | 03/12/12 14:27 |
| Precision rectifier is suitable for any waveform | Kalpak Dabir | 03/13/12 01:47 |
| are u sure?? | Yagnesh Mehta | 03/13/12 08:03 |
| Depends | Per Westermark | 03/13/12 09:08 |
| must be severely bandwidth limited | Erik Malund | 03/13/12 09:11 |
| Maybe was circuit with top-voltage capacitor | Per Westermark | 03/13/12 09:17 |
| Sorry for confusion | Yagnesh Mehta | 03/14/12 00:18 |
| What accuracy do you need? | Kalpak Dabir | 03/14/12 01:23 |
| 360/1024 | Yagnesh Mehta | 03/14/12 01:41 |
| Not what he (or me) have asked | Per Westermark | 03/14/12 04:39 |
| you are right.... | Yagnesh Mehta | 03/14/12 11:51 |
| Do you believe you can protect your circuit from noise? | Richard Erlacher | 03/14/12 08:19 |
| Very Noisy environment | Yagnesh Mehta | 03/14/12 11:57 |
| re Very Noisy environment | Erik Malund | 03/14/12 12:23 |
| Some of those rules are showing their age | Richard Erlacher | 03/14/12 20:00 |
| here we go again | Erik Malund | 03/15/12 08:15 |
| think about this for a minute | Richard Erlacher | 03/15/12 17:10 |
| when discussing a FAQ | Erik Malund | 03/16/12 06:49 |
| Well, when were those cap sizes determined? | Richard Erlacher | 03/16/12 09:53 |
| Technology | Per Westermark | 03/16/12 10:13 |
| Steady state currents do not need decaps | Kalpak Dabir | 03/16/12 22:48 |
| Often low capacitance so limited charge. But remember load. | Per Westermark | 03/17/12 06:41 |
| fixations | Erik Malund | 03/16/12 10:40 |
| Nothing. has been proven yet. | Richard Erlacher | 03/18/12 13:15 |
| once more for the peanut gallery | Erik Malund | 03/19/12 07:23 |
| Where you sit determines what you see ... | Richard Erlacher | 03/20/12 01:56 |
| Off-topic | Per Westermark | 03/20/12 02:01 |
| difficult when ... | Erik Malund | 03/20/12 06:59 |
| Yes ... I don't know how we got here either | Richard Erlacher | 03/20/12 09:32 |
i do | Erik Malund | 03/20/12 09:45 |