afs600 Actel Corporation, afs600 Datasheet - Page 49

• Manufacturer Part Number: afs600
• Description: Actel Fusion Programmable System Chips Mixed-signal Family With Optional Arm Support
• Manufacturer: Actel Corporation

Crystal Oscillator (Xtal Osc)
When used as the clock source for the RTC, the crystal
oscillator will be configured by the RTC with the
RTCXTLMODE[1:0] RTC macro pins. Refer to the
Oscillator" section on page 2-20
crystal oscillator operation.
The crystal oscillator input to the RTC is divided by 128, so
bit 0 of the RTC toggles at the frequency of the crystal
oscillator divided by 128. The frequencies of the RTC are
gated by those of the crystal oscillator, from 32.768 kHz to
20 MHz. When used with a 32.768 kHz crystal, bit 0 of the
of RTC has a period of ~7.8 ms, and bit 7 has a period of
1 second.
Voltage Regulator (VR) Initialization (Init)
The VR Init block determines voltage regulator behavior
when the 3.3 V supply is valid. The Fusion devices
support different use models. Some of these require the
1.5 V voltage regulator to turn on when the 3.3 V supply
is stable. Other use models require additional conditions
to be met before the 1.5 V VR turns on. Since the FPGA is
not operating when the 3.3 V supply is off, the VR Init
block lets the user define VR behavior at design time.
Two bits can be set within the core, which bits the VR Init
block will read as it comes out of reset and either turn on
the VR or leave it in an off state.
Figure 2-29 • Voltage Regulator
RTC FPGA
Power-Up/Down Control Circuit
for specific details on
Regulator
PDVR
1.5 V
"Crystal
A d v an c ed v1 . 4
Voltage Regulator Logic
The VR Logic block, along with the VR, combines
commands from the FPGA, RTC, VR Init block, V
detector, and PUB pad to determine whether or not the
VR is enabled.
The VR can be enabled from several sources: the PUB pin,
the RTC_MATCH signal from the RTC block, or triggered
by the VR Init block. Once triggered, the VR will remain
on. Only the FPGA fabric can disable the VR, unless the
V
reset occurs.
1.5 V Voltage Regulator
The VR generates a 1.5 V power supply from the 3.3 V
power supply. The 1.5 V output is intended to supply all
1.5 V needs of the Fusion device. This regulator requires
an external bipolar pass transistor
can drive up to 20 mA of current through the PTBASE
pad. The amount of 1.5 V current available is dependent
upon the gain of the external pass transistor used.
Enable for this block is generated in the VR Logic block
or from the PUB pin.
The VR is forced "on" with TRST high or floating
(internal pull-up), so an external pull-down is required
on TRST if the customer desires to power-down the VR.
The 1.5 V is not supplied internally to the Fusion device.
It must be routed externally to the V
device. Therefore the user is not required to use the VR
and can use an off-chip 1.5 V supply if desired.
CC33A
supply falls below the V
V
On-Chip Off-Chip
PTBASE
CC33A
PTEM
1 µA
Actel Fusion Programmable System Chips
PUB
V
CC33A
V
CC33A
1.5 V Out
CC33UP
(Figure
threshold and a
CC
2-29). The VR
pins on the
CC33UP
2-35