Question on Datasheet POR

[FreshmanNewbie]

In this datasheet, page 1, block diagram, why is the VDD connected to POR?

1. Why is the VDD connector to POR?

2. Is there POR for this IC? I couldn't find the value on the datasheet.
I found the 1us - TABLE 2-1, page 24. Is this 1us POR?

3. Since POR block is connected to VDD? How should I handle the RESET pin?

Please help me on how to handle VDD and RESET pins? And some understanding on POR will help me.

 

[FvM]

POR feature is completely specified on page 5, 1.2 Power-on Reset (POR).
Reset is optionally and may be used or not.

 

[KlausST]

Hi,

VDD is the power supply. As always.

RESET clearly is described as low_active RESET input. Nothing special.

Section 1.2 describes the POR circuit and function. Read it.
POR is the on-chip generated "POWER ON RESET". If it was not connected to the POWER supply (VDD) .. how was it able to monitor the power supply (VDD)?
I don´t get what you are asking for / what is unclear.

1. Why is the VDD connector to POR?

Let´s say you want to measure the pressure of your tyre (i.e. monitor power supply voltage VDD)
It should be quite obvious that one needs to connect the pressure sensor (POR) with the tyre pressure (VDD).
It just makes sense that it is connected this way internally. Do you see any option?

2. Is there POR for this IC?

Why do you ask? You even referred to the block diagram on page1.
And the datasheet clearly describes it and it´s function.

I couldn't find the value on the datasheet.
I found the 1us - TABLE 2-1, page 24. Is this 1us POR?

What "value" do you expect?
Voltage and timing specifications are given in D001, D002, D003. What else do you need?

Klaus

--- Updated Jan 4, 2024 ---

Reset is optionally and may be used or not.

Still it needs to be connected externally.
General rule: Don´t leave any (unused) input left floating unless otherwise mentioned. This applies for analog as well as digital inputs.

 

[FreshmanNewbie]

Hi,

VDD is the power supply. As always.

RESET clearly is described as low_active RESET input. Nothing special.

Section 1.2 describes the POR circuit and function. Read it.
POR is the on-chip generated "POWER ON RESET". If it was not connected to the POWER supply (VDD) .. how was it able to monitor the power supply (VDD)?
I don´t get what you are asking for / what is unclear.


Let´s say you want to measure the pressure of your tyre (i.e. monitor power supply voltage VDD)
It should be quite obvious that one needs to connect the pressure sensor (POR) with the tyre pressure (VDD).
It just makes sense that it is connected this way internally. Do you see any option?


Why do you ask? You even referred to the block diagram on page1.
And the datasheet clearly describes it and it´s function.


What "value" do you expect?
Voltage and timing specifications are given in D001, D002, D003. What else do you need?

Klaus

--- Updated Jan 4, 2024 ---

Still it needs to be connected externally.
General rule: Don´t leave any (unused) input left floating unless otherwise mentioned. This applies for analog as well as digital inputs.

I would actually like to know what is the POR level for this IC.

Suppose, my power supply VDD, is 3.3V. And if I turn off the supply, it takes time to reduce. Slowly, it comes to 3V, 2.5V, 2.2V, 1.2V ... and then 0V. What happens suppose, when the decreasing voltage is around, say 1.2V, and at that moment, I provide power to VDD again. What's the threshold level above and below for the POR. I couldn't find in the datasheet?

Also, I have just pulled-up my RESET pin to 3.3V using 100k. Is it OK?

 

[KlausST]

Hi,

I would actually like to know what is the POR level for this IC.

I´ve already told you, whats given by the datasheet: D001.

You are free to use external RESET circuit for voltage threshold of your need.

Also, I have just pulled-up my RESET pin to 3.3V using 100k. Is it OK?

* Voltage across the pull up resistor: (supply voltage - V_IH_min) = VDD - D041 = 0.2 x VDD
* Current through the resistor: I_IL (D060)
--> use Ohm´s law to calculate maximum allowed resistor value.

Klaus

 

[FreshmanNewbie]

Hi,

I´ve already told you, whats given by the datasheet: D001.

You are free to use external RESET circuit for voltage threshold of your need.


* Voltage across the pull up resistor: (supply voltage - V_IH_min) = VDD - D041 = 0.2 x VDD
* Current through the resistor: I_IL (D060)
--> use Ohm´s law to calculate maximum allowed resistor value.

Klaus

Ok, so once the VDD supply reaches VDD = 1.8V, the RESET is released by the device?

--- Updated Jan 5, 2024 ---

Hi,

I´ve already told you, whats given by the datasheet: D001.

You are free to use external RESET circuit for voltage threshold of your need.


* Voltage across the pull up resistor: (supply voltage - V_IH_min) = VDD - D041 = 0.2 x VDD
* Current through the resistor: I_IL (D060)
--> use Ohm´s law to calculate maximum allowed resistor value.

Klaus

This line is not clear, "The on-chip POR circuit holds the device in Reset untilVDD has reached a high enough voltage to deactivatethe POR circuit".

How does high enough imply? What voltage can be considered as high enough?

 

[FvM]

POR threshold level isn't clearly specified in the datasheet. Obviously it's below minimal Vdd of 1.8V. Datasheet specs suggest that Vdd must rise from zero with a certain rate to trigger POR.

Question, is the exact information essential for your application?

 

[KlausST]

Hi,

It´s a POR circuit .. and it does what it´s name says. It RESETs the device on POWER_ON.
* power OFF your device. OFF! Not just "lower the voltage a bit".
* then switch POWER ON
* and it will RESET the device.

As the description says: it gives the registers their default state and it gives the interface a default state.
* it is not a BROWN_OUT reset which detects short power outages
* it is not a microcontroller supervisory device with accurate RESET_thresholds.

And as I and FvM already stated: If you want something more accurate, you are free to use your own circuit and feed your RESET signal to he device´s RESET input.

Usually this device is controlled by some master (microcontroller, PLD...). This MASTER is the more critical device and should have a more accurate RESET behaviour and should control the connected devices.
* so you may use the MC´s internal RESET circuitry and generate a RESET signal (Port pin) for connected devices.
* you may use an external RESET device to be fed to MC and slave devices
* or you may use a "software_only" reset strategy for the slaves.

So you are free .. you have all the choices.

Klaus

 

[FreshmanNewbie]

POR threshold level isn't clearly specified in the datasheet. Obviously it's below minimal Vdd of 1.8V. Datasheet specs suggest that Vdd must rise from zero with a certain rate to trigger POR.

Question, is the exact information essential for your application?

D002 - Can you please explain what this specification implies. Because the typical value is Vss.

What I understand is that, POR will be released when VDD is > Vss. Which means, whenever VDD is > VSS, POR goes High and RESET is deasserted. In that case, What would be the voltage on the RESET pin?

 

[KlausST]

Hi,

D002 - Can you please explain what this specification implies. Because the typical value is Vss.

VSS = GND = 0V
It simply means that the POR circuit works down to zero supply voltage.
This may sound suspicious, because no semiconductor can work down to 0V supply voltage. Instead it means the POR output (let´s say it is a low_active signal) is pulled low by an internal resistor. And even if all semiconductors are inactive (because of too low supply voltage) the level is valid because of the passive resistor.

What I understand is that, POR will be released when VDD is > Vss.

No.
POR will be released when VDD is in a valid (operable) range.

What would be the voltage on the RESET pin?

The RESET pin is an input.The IC does not drive any voltage to that pin.
Instead you are responsible for a valid level on the RESET pin!
Thus we can not answer this question. Indeed you are the one who needs to answer this question.

Klaus