ATMEGA406_0607 Datasheet, PDF (123/263 Pages) ATMEL Corporation – 8-bit Microcontroller with 40K Bytes In-System Programmable Flash

ATmega406
21.3 Register Description for Voltage Reference and Temperature Sensor
21.3.1
BGCCR – Bandgap Calibration C Register
Bit
7
6
(0xD0)
BGEN
–
Read/Write
R
R
Initial Value
0
0
5
BGCC5
R/W
0
4
BGCC4
R/W
0
3
BGCC3
R/W
0
2
BGCC2
R/W
0
1
BGCC1
R/W
0
0
BGCC0
R/W
0
BGCCR
• Bit 7 - BGEN
This bit is not available from revision E and on of the ATmega406. A complete description is
found in the revision A of this document.
• Bit 6 – Res: Reserved Bit
This bit is reserved for future use.
• Bit 5:0 – BGCC5:0: BG Calibration of PTAT Current
These bits are used for trimming of the nominal value of the bandgap reference voltage. These
bits are binary coded. Minimum VREF: 000000, maximum VREF: 111111. Step size approxi-
mately 2 mV.
21.3.2
BGCRR – Bandgap Calibration R Register
Bit
(0xD1)
Read/Write
Initial Value
7
BGCR7
R/W
0
6
BGCR6
R/W
0
5
BGCR5
R/W
0
4
BGCR4
R/W
0
3
BGCR3
R/W
0
2
BGCR2
R/W
0
1
BGCR1
R/W
0
0
BGCR0
R/W
0
BGCRR
• Bit 7:0 – BGCR7:0: BG Calibration of Resistor ladder
These bits are used for temperature gradient adjustment of the bandgap reference. Figure 21-2
illustrates VREF as a function of temperature. VREF has a positive temperature coefficient at
low temperatures and negative temperature coefficient at high temperatures. Depending on the
process variations, the top of the VREF curve may be located at higher or lower temperatures.
To minimize the temperature drift in the temperature range of interest, BGCRR is used to adjust
the top of the curve towards the centre of the temperature range of interest. The BGCRR bits are
temperature coded resulting in 9 possible settings: 00000000, 00000001, 00000011, 00000111,
… , 11111111. The value 00000000 shifts the top of the VREF curve to the highest possible
temperature, and the value 11111111 shifts the top of the VREF curve to the lowest possible
temperature.
2548E–AVR–07/06
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