4–6
Chapter 4: Hot Socketing and Power-On Reset in MAX II Devices
Power-On Reset Circuitry
Power-Up Characteristics
When power is applied to a MAX II device, the POR circuit monitors VCCINT and
begins SRAM download at an approximate voltage of 1.7 V or 1.55 V for MAX IIG and
MAX IIZ devices. From this voltage reference, SRAM download and entry into user
mode takes 200 to 450 µs maximum, depending on device density. This period of time
is specified as tCONFIG in the power-up timing section of the DC and Switching
Characteristics chapter in the MAX II Device Handbook.
Entry into user mode is gated by whether all VCCIO banks are powered with sufficient
operating voltage. If VCCINT and VCCIO are powered simultaneously, the device enters
user mode within the tCONFIG specifications. If VCCIO is powered more than tCONFIG after
VCCINT, the device does not enter user mode until 2 µs after all VCCIO banks are powered.
For MAX II and MAX IIG devices, when in user mode, the POR circuitry continues to
monitor the VCCINT (but not VCCIO) voltage level to detect a brown-out condition. If
there is a VCCINT voltage sag at or below 1.4 V during user mode, the POR circuit resets
the SRAM and tri-states the I/O pins. Once VCCINT rises back to approximately 1.7 V
(or 1.55 V for MAX IIG devices), the SRAM download restarts and the device begins
to operate after tCONFIG time has passed.
For MAX IIZ devices, the POR circuitry does not monitor the VCCINT and VCCIO voltage
levels after the device enters user mode. If there is a VCCINT voltage sag below 1.4 V
during user mode, the functionality of the device will not be guaranteed and you
must power down the VCCINT to 0 V for a minimum of 10 µs before powering the VCCINT
and VCCIO up again. Once VCCINT rises from 0 V back to approximately 1.55 V, the
SRAM download restarts and the device begins to operate after tCONFIG time has
passed.
Figure 4–5 shows the voltages for POR of MAX II, MAX IIG, and MAX IIZ devices
during power-up into user mode and from user mode to power-down or brown-out.
1
All VCCINT and VCCIO pins of all banks must be powered on MAX II devices before
entering user mode.
MAX II Device Handbook
© October 2008 Altera Corporation
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