AN2339
Power supply
5/20
2 Power
supply
Figure 1.
Power Supply Overview
2.1
Main operating voltages
The STR91x devices are processed in 0.18 µm technology, ARM966E-S RISC core and I/O
peripherals need different power supplies. In fact, STR91x requires two separate operating
voltage supplies. The CPU and memories operate in a range from 1.65V to 2.0V on the
VDD pins, and the I/O ring operates in the 2.7V to 3.3V or 3.0V to 3.6V range on the VDDQ
pins.
All pins need to be properly connected to the power supplies. These connections, including
pads, tracks and vias should have an impedance as low as possible. This is typically
achieved with thick track widths and preferably dedicated power supply planes in multi-layer
PCBs.
In addition, each VDD/VSS and VDDQ/VSSQ pair should be decoupled with ceramic
capacitors which need to be placed as close as possible to the appropriate pins or below the
pins on the contrary side of the PCB. Typical values are 10nF to 100nF, but exact values
depend on the application needs. The following figure shows the typical layout on such a
VDD/VSS pair.
A/D converter
AV
DD
V
DDQ
V
DD
AV
SS
Core
(3V or 3.3V)
SRAM
AV
REF
RTC
V
BATT
V
SSQ
I/O Ring
V
SS
(1.8V)
Note 1
(from 1V
(V
DDQ
)
(V
DDQ
)
up to V
DDQ
)
V
DD
Core
SRAM
RTC
V
BATT
V
SS
(1.8V)
Note 1
(V
DDQ
)
A/D converter
AV
REF_
AV
DD
V
DDQ
AV
SS_
V
SSQ
(3V or 3.3V)
V
SSQ
I/O Ring
(V
DDQ
)
128-pin devices
80-pin devices
Note1: You can connect power to the SRAM with VBATT by firmware