Hello, my name is Bee. Last time I studied about Power-On Reset (POR) and initialization, but my senior pointed out to me that the POR circuit monitors different power supplies for each device family.
Power Supplies Monitored for Device Families and POR Circuits
Cyclone® IV monitored the following three power supplies
- VCCINT
- VCCIO
- VCCA
So which supply voltages do the other device families monitor? According to the MAX® V handbook, since there are two power supplies used for MAX V (VCCINT and VCCIO), the following two power supplies are monitored.
- VCCINT
- VCCIO
MAX V Handbook : Power-On Reset Circuitry
For Stratix® IV devices, which have many power supply systems, five power supply systems are monitored.
So, it is clear that different device families have different supply voltages monitored by the POR circuitry.
Time for MAX V to enter user mode
So, is there a POR time specification in MAX V? Or is there a provision for other power supplies?
When I looked at the POR section in the MAX V handbook, I found no mention of tPOR (Power-On Reset Time).
On the other hand, the configuration time is specified in tCONFIG, with a maximum value of 200 to 500us.
(The maximum value varies depending on the model number.) The maximum value for each model number is shown in the figure below.
After power-on, configuration is executed and the device is in user mode. The graph below shows the relationship between voltage and time from power-on to transition to user mode.
The graph shows that 1.55V triggers the configuration, which is completed after a maximum of tCONFIG (200 to 500us).
If you look at this graph carefully, you will see that VCCINT transitions to 1.8V when the configuration ends....
Does this mean that VCCINT must transition from 1.55V to 1.8V during tCONFIG (200 to 500us)?
I read through the handbook a little more and found the conditions for entering user mode.
Conditions to enter user mode
The condition to enter user mode seems to be when VCCINT and VCCIO reach the specified value. In other words, it is not necessary to go from 1.55V to 1.8V between 200 and 500us.
Order of power-on |
Time to enter user mode |
VCCINT and VCCIO supplied simultaneously |
Within tCONFIG |
VCCIO is supplied after tCONFIG after VCCINT is supplied |
2us after VCCIO of all I/O banks is supplied and meets the specified value |
Since MAX V devices are instant-on devices, there is no POR time specification; the time for configuration (tCONFIG) and the power requirements to enter user mode were published.
Conclusion
Different devices have different supply voltages monitored by the POR circuit.
The condition for MAX V to enter user mode is after the supply voltage VCCIO , VCCINT reaches the specified value.