Actel Fusion Mixed-Signal FPGAs
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 (Figure 2-29). The VR 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 VCC pins
on the device. Therefore the user is not required to use the VR and can use an off-chip 1.5 V supply
if desired.
On-Chip Off-Chip
VCC33A
RTC FPGA
VCC33A
PTBASE
1.5 V
Regulator
PTEM
1.5 V Out
PDVR
VCC33A
1 µA
PUB
Power-Up/Down Control Circuit
Figure 2-29 • Voltage Regulator
Preliminary v1.7
2-39
ACTEL [ Actel Corporation ]
