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1745D–ATARM–04-Nov-05
AT91M55800A
7. Product Overview
7.1 Power Supplies
The AT91M55800A has 5 kinds of power supply pins:
• VDDCORE pins, which power the chip core
• VDDIO pins, which power the I/O Lines
• VDDPLL pins, which power the oscillator and PLL cells
• VDDA pins, which power the analog peripherals ADC and DAC
• VDDBU pins, which power the RTC, the 32768 Hz oscillator and the Shut-down Logic of
the APMC
VDDIO and VDDCORE are separated to permit the I/O lines to be powered with 5V, thus
resulting in full TTL compliance.
The following ground pins are provided:
• GND for both VDDCORE and VDDIO
• GNDPLL for VDDPLL
•GNDA for VDDA
• GNDBU for VDDBU
All of these ground pins must be connected to the same voltage (generally the board electric
ground) with wires as short as possible. GNDPLL, GNDA and GNDBU are provided sepa-
rately in order to allow the user to add a decoupling capacitor directly between the power and
ground pads. In the same way, the PLL filter resistor and capacitors must be connected to the
device and to GNDBU with wires as short as possible. Also, the main oscillator crystal and the
32768 Hz crystal external load capacitances must be connected respectively to GNDPLL and
to GNDBU with wires as short as possible.
The main constraints applying to the different voltages of the device are:
• VDDBU must be lower than or equal to VDDCORE
• VDDA must be higher than or equal to VDDCORE
• VDDCORE must be lower than or equal to VDDIO
The nominal power combinations supported by the AT91M55800A are described in the follow-
ing table:
7.2 Input/Output Considerations
After the reset, the peripheral I/Os are initialized as inputs to provide the user with maximum
flexibility. It is recommended that in any application phase, the inputs to the AT91M55800A
microcontroller be held at valid logic levels to minimize the power consumption.
Table 7-1. Nominal Power Combinations
VDDIO VDDCORE VDDA VDDPLL VDDBU
Maximum Operating
Frequency
3V 3V 3V 3V 3V 33 MHz
3.3V 3.3V 3.3V 3.3V 3.3V 33 MHz
5V 3.3V 3.3V 3.3V 3.3V 33 MHz