Howdy. I am trying to understand ATX power supplies better and how I might manage Power On and Power Good with a Texas Instruments TPS3510 PC power supply supervisor with +12V/+5V/+3.3V linear rails.
As a novice I am getting rather confused.
I've read the ATX spec ver 2.2 and the associated ATX12V Power Supply Design Guide. I get that PS_ON# from the motherboard via pin 16 of the main power connector is a signal from the computer motherboard intended to turn on the power rails. In my application, I was thinking the 3.3/5/12V rails would simply be on all the time (unless the AC was disconnected) and not be drawing current except for the standby requirements because the motherboard would basically be off.
I also get that the power supply must deliver a PWR_OK signal to the motherboard via pin 8 of the main power connector which indicates the +5VDC and +3.3VDC voltages are good.
Now to the TPS3510. Pins 2, 5, 6 and 7 are clear (GND and the latter three simply connected to the 3.3V, 5V and 12V rails). Pin 4 should, I presume, be connected to pin 16 of the main power connector. Output pin 8 - PGO - should, I presume, be connected to pin 8 of the main power connector. First question: Why the resistor across pins 6 and 8 and how to determine an appropriate value?
I am horribly confused by input pin 1 "PGI" and output pin 3 "FPO". "Typical application" shows the PGI or Power Good Input connected to a voltage divider and with a recommended operating condition of VDD + 0.3V. I thought the TPS3510 sourced power via pin 7 VDD. PGI is monitored for Power Good. Second question: to what should PGI be connected and how to determine the appropriate value of the resistors? Fault Protect Output, FPO, is an "inverted fault protection output, open drain output stage" but is shown in Typical Application as a being connected to the 5V standby rail via a LED and resistor. Third question: I'm confused by an output pin being connected to a 5V rail unless this is simply to power the (red) LED to indicate a fault condition (fault condition => current drawn from 5VSB and LED lights)? While I have read the detailed description of the interaction of PSON and FPO several times I am still not getting it.
Any help appreciated.
Steve
As a novice I am getting rather confused.
I've read the ATX spec ver 2.2 and the associated ATX12V Power Supply Design Guide. I get that PS_ON# from the motherboard via pin 16 of the main power connector is a signal from the computer motherboard intended to turn on the power rails. In my application, I was thinking the 3.3/5/12V rails would simply be on all the time (unless the AC was disconnected) and not be drawing current except for the standby requirements because the motherboard would basically be off.
I also get that the power supply must deliver a PWR_OK signal to the motherboard via pin 8 of the main power connector which indicates the +5VDC and +3.3VDC voltages are good.
Now to the TPS3510. Pins 2, 5, 6 and 7 are clear (GND and the latter three simply connected to the 3.3V, 5V and 12V rails). Pin 4 should, I presume, be connected to pin 16 of the main power connector. Output pin 8 - PGO - should, I presume, be connected to pin 8 of the main power connector. First question: Why the resistor across pins 6 and 8 and how to determine an appropriate value?
I am horribly confused by input pin 1 "PGI" and output pin 3 "FPO". "Typical application" shows the PGI or Power Good Input connected to a voltage divider and with a recommended operating condition of VDD + 0.3V. I thought the TPS3510 sourced power via pin 7 VDD. PGI is monitored for Power Good. Second question: to what should PGI be connected and how to determine the appropriate value of the resistors? Fault Protect Output, FPO, is an "inverted fault protection output, open drain output stage" but is shown in Typical Application as a being connected to the 5V standby rail via a LED and resistor. Third question: I'm confused by an output pin being connected to a 5V rail unless this is simply to power the (red) LED to indicate a fault condition (fault condition => current drawn from 5VSB and LED lights)? While I have read the detailed description of the interaction of PSON and FPO several times I am still not getting it.
Any help appreciated.
Steve
Hi,
The resistor between pins 6 and 8 is to provide the pull up voltage for the PGO pin which is an open collector driver (it can only pull to GND).
So for this connection PGO is either 0V or 5V. A value of 1K to 10K is probably fine.
The PGI input is to allow an external power good signal to be fed through the chip (and have the power good 3V3 and 5V added to it).
The connection to pin 3 is just to light the LED when there not FPO output is active (low).(A series resistor of a few hundred ohms to 1K depending on the current required by the led is needed).
Hope this helps
Bruce
The resistor between pins 6 and 8 is to provide the pull up voltage for the PGO pin which is an open collector driver (it can only pull to GND).
So for this connection PGO is either 0V or 5V. A value of 1K to 10K is probably fine.
The PGI input is to allow an external power good signal to be fed through the chip (and have the power good 3V3 and 5V added to it).
The connection to pin 3 is just to light the LED when there not FPO output is active (low).(A series resistor of a few hundred ohms to 1K depending on the current required by the led is needed).
Hope this helps
Bruce
Hi Bruce
Thanks for taking the time to respond. Okay I think I understand 6/8. It sources voltage/current from the 5V rail, when it "goes low" that current sinks (is pulled) to ground? When it "goes high" the current flows to pin 8 on the main power connector indicating power good? The resistor just limits the current that can flow to the main connector. I'm still getting used to the terminology. Do I have this right?
If I understand your response re PGI this wouldn't be used in my application? It can remain unconnected?
At least I was on the right track re FPO. LED lit implies fault or all good? (To help me decide colour of LED 😉 )
Thanks for taking the time to respond. Okay I think I understand 6/8. It sources voltage/current from the 5V rail, when it "goes low" that current sinks (is pulled) to ground? When it "goes high" the current flows to pin 8 on the main power connector indicating power good? The resistor just limits the current that can flow to the main connector. I'm still getting used to the terminology. Do I have this right?
If I understand your response re PGI this wouldn't be used in my application? It can remain unconnected?
At least I was on the right track re FPO. LED lit implies fault or all good? (To help me decide colour of LED 😉 )
Last edited:
Bruce or others I'm really hoping you can come back to me on the questions above. Thanks in advance Steve
I have come back to this after a being distracted on other projects. It seems to have done some good as well. I think I have (finally) got all of this figured out. I am just stuck on the diodes.
A search of Mouser for general purpose diodes with a 0.5V drop doesn't yield many options. Adding the max current sink of FPO and PGO yields 30mA (with actual being a bit over half that). I also know the diodes need to be rated for 12V. So it would seem that this is one of the few candidates:
BAS 52-02V H6327 Infineon Technologies | Mouser
Unless I am doing something wrong? I have to admit to being very daunted by an SMT part that's merely 1.6mm long...
An externally hosted image should be here but it was not working when we last tested it.
A search of Mouser for general purpose diodes with a 0.5V drop doesn't yield many options. Adding the max current sink of FPO and PGO yields 30mA (with actual being a bit over half that). I also know the diodes need to be rated for 12V. So it would seem that this is one of the few candidates:
BAS 52-02V H6327 Infineon Technologies | Mouser
Unless I am doing something wrong? I have to admit to being very daunted by an SMT part that's merely 1.6mm long...
Last edited:
Hi Steve,
wonder you have any success with this? I two keen to build a linear PSU ATX.
Any update are grateful!
Many thanks in advance!
Chanh.
wonder you have any success with this? I two keen to build a linear PSU ATX.
Any update are grateful!
Many thanks in advance!
Chanh.
Hi. Have a look at this thread.
It all seems to work on the bench when I force PS_ON low as I understand the motherboard would do when the front panel standby button is pressed. I couldn't test with a motherboard because I had problems with my mobo before I go there. I am just now assembling the CPU and memory into a new mobo and should be able to test soon.
It all seems to work on the bench when I force PS_ON low as I understand the motherboard would do when the front panel standby button is pressed. I couldn't test with a motherboard because I had problems with my mobo before I go there. I am just now assembling the CPU and memory into a new mobo and should be able to test soon.
- Status
- Not open for further replies.