sam7 hardware considerations frederic boyer at91 support group. version 1.0 october 2006

SAM7 Hardware Considerations

Frederic BOYER

AT91 Support Group.Version 1.0 October 2006

2 Apr-06 ARM-Based Products Group

AT91SAM7 Power Supply Strategies

• 3.3V Single Power Supply Strategy: On-chip Voltage Regulator Used

• 1.8V & 3.3V Dual Power Supply Strategy:

• On-chip Voltage Regulator not Used and ADC used.

• On-chip Voltage Regulator and ADC not used.


AT91SAM7 Power Supply Strategies (cont.)

3.3V Single Power Supply (On-chip Voltage Regulator Used) :

Decoupling Capacitors on all Power Supplies



VDDIN: Voltage regulator Input and ADC (3.3V).

VDDIO: I/O lines (3.3V) and USB transceivers (SAM7S).

VDDFLASH: Flash (3.3V) and USB transceivers (SAM7X/XC/SE).


VDDIN must be connected

to a decoupling/filtering capacitor

to improve start-up stability

and reduce source voltage drop



VDDOUT: Voltage regulator Output (1.8V).

VDDCORE: On-chip RC, Device and Flash logic (1.8V).

VDDPLL: Main Oscillator and PLL (1.8V).


VDDOUT must be connected


to guarantee 1.8V stability



3.3V & 1.8V Dual Power Supplies(On-chip Voltage Regulator NOT Used and ADC used):




VDDIN: ADC Only (3.3V).




VDDIN must be connected







VDDCORE: On-chip RC, Device and Flash (1.8V).


VDDOUT must be connected


to prevent on-chip voltage regulator

oscillations

On-chip Voltage Regulator must be in Idle mode



3.3V & 1.8V Dual Power Supplies(On-chip Voltage Regulator and ADC NOT Used):







VDDIO must be connected




VDDIN connected to GND




VDDCORE: On-chip RC, Device and Flash (1.8V).


VDDCORE must be connected




VDDOUT can be left

unconnected


SAM7 Typical Power Supply Pins Configuration


SAM7 Power Supply Constraints

3.3V Single Power Supply:

VDDCORE (so VDDIN) slope must be superior or equal to 6V/ms.

3.3V & 1.8V Dual Power Supply:

VDDCORE slope must be superior or equal to 6V/ms.

VDDFLASH must always be superior or equal to VDDCORE. SAM7

SAM7S

SAM7X

SAM7S

SAM7X


Clock, Oscillator and PLL

Crystal (Main Oscillator in Normal Mode): XIN and XOUT

Main Oscillator range: 3 to 20 MHz.

Crystal Load capacitance to check (CCRYSTAL).

Internal Equivalent Load Capacitance (CL) is:

11 pF (SAM7SE32).

20 pF (other SAM7).

1 kOhm resistor on XOUT only required for crystals with frequencies lower than 8 MHz.


Clock, Oscillator and PLL (cont.)

Crystal (Main Oscillator in Normal Mode): XIN and XOUT

The crystal load capacitance (CCRYSTAL) is the equivalent capacitor value that circuit must “show” to the crystal in order to oscillate at the target frequency.

Cload = CCRYSTAL - CL

Example: CCRYSTAL = 20pF (SAM7S-EK, SAM7X-EK and SAM7SE-EK)

AT91SAM7SE32: 18pF external capacitors are required on XIN and XOUT. External capacitor 2*Cload = 2*(CCRYSTAL - CL) = 2*(20-11) = 18pF

Other AT91SAM7: no need to add external capacitors. (Cload = 0pF).



External Clock (Main Oscillator in Bypass Mode): XIN

External Clock Range: up to 50 MHz.

Duty Cycle: 40-60%

1.8V Square Wave signal (VDDPLL).

XOUT can be left unconnected



PLL Filter: PLLRC pin

PLL Filter calculation tool.

ATMEL_PLL_LFT_Filter_CALCULATOR_AT91_xxx.xls

3 Values necessary to compute the correct filter:

Fin: Quartz Frequency

MUL: PMC Multiplier (MUL+1)

DIV: PMC Divider (DIV)

Adjust R-C1-C2 for startup time.

If PLL not used,PLLRC can be left unconnected


ICE & JTAG

TDI, TCK, TMS and TDO: No internal Pull-up resistors.

Pull-up on TDI, TCK, TMS to reduce power consumption.


ICE & JTAG (cont.)

JTAGSEL pin: Internal Pull-down resistor (15 kOhm).

JTAGSEL=0 (Default value): JTAG/ICE interface selected.

Can be left unconnected for normal operations.

JTAGSEL=1 : must be tied to VDDIO to enter JTAG Boundary Scan.


ERASE pin

Internal Pull-down resistor (15 kOhm).

ERASE=0 (Default value): no action.


ERASE=1 : must be tied to VDDIO to erase:

• Flash content

• GPNVM bits

• Security Bit

Debouncing Time (On-chip RC):

SAM7S: none (4µs)

SAM7X/XC: 200 ms

SAM7SE: 220 ms


Reset

POR (Power On Reset) on VDDCORE

Reset the whole system.

RESET (NRST pin)

NRST is configured as output at power-up.

Internal Pull-up resistor on VDDIO for User/External Reset control:

SAM7S/X/XC: 10 kOhm

SAM7SE: 100 kOhm

Can be left unconnected.

No constraintson the reset pulse length(Built-in POR)


TST pin

Internal Pull-down resistor (15 kOhm)

TST=0 (Default value): no action.


TST=1 : Product dependant

Must be tied to VDDIO to enter:

• FFPI mode (PA0=PA1=1 and PA2=0)

• Or SAM-BA Boot recovery mode (PA0=PA1=PA2=1)(only for SAM7S).


PIO

I/O Lines

Pulled-up Input at reset:

SAM7S/X/XC: 10 kOhm

SAM7SE: 100 kOhm

4 High drive current I/O lines (16mA)Other I/O lines: 8mA

5V tolerant (SAM7S/X/XC only)

Schmitt trigger inputs (SAM7SE only)

Unused I/O: Should be configured as output driven at ‘0’, pull-up disabled to reduce power consumption.


ADC

If the ADC Controller is not used:

ADVREF

AD4

AD5

AD6

AD7

Should be connected to GND to reduce power consumption.

Pure Analog Inputs


USB (SAM7S/X/XC)

No Internal Pull-up: external circuitry necessary to enable the pull-up.

No Internal Pull-down.

Host disconnected DDP must be disconnected (self powered design) DDP and DDM are floating Over consumptionSolution: 330 kOhm pull-down on DDP and DDM to reduce over consumption.

Built-in Transceiver Enabled by default: may be disabled to reduce power consumption.

VBUS monitoring circuitry necessary to remove the pull-up

when the host switches off


USB (SAM7SE)

Internal Pull-up: 1.5 kOhm pull-up (disabled by default): No need for an external pull-up circuitry !

No Internal Pull-down.

Host disconnected DDP must be disconnected (self powered design) DDP and DDM are floating Over consumptionSolution: 330 kOhm pull-down on DDP and DDM to reduce over consumption.

Built-in Transceiver Disabled by default.

VBUS monitoring circuitry necessary to remove the pull-up

when the host switches off


USB

If the USB Device Controller is not used, to reduce power consumption:

DDP must be:

Tied to VDDIO (SAM7S).

Tied to VDDFLASH (SAM7X/XC).

Left floating (SAM7SE).

DDM must be:

Tied to GND (SAM7S/X/XC).

Left floating (SAM7SE).

.


SDCK pin (SAM7SE only)

SDCK (SDRAM Clock)

SDCK is tied low after reset.

Output-only without pull-up and not 5V-tolerant

Maximum Output Frequency:

48.2 MHz for VDDIO from 3.0V to 3.6V

25 MHz for VDDIO from 1.65V to 1.95V

SAM7SE Only !

sam7 hardware considerations frederic boyer at91 support group. version 1.0 october 2006

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