Datasheet
119
8024A–AVR–04/08
ATmega8HVA/16HVA
21.3.2 BGCRR – Bandgap Calibration R Register
• 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
thermometer 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.
Figure 21-2. Illustration of VREF as a function of temperature.
Bit 7 6 5 4 3 2 1 0
(0xD1) BGCR7 BGCR6 BGCR5 BGCR4 BGCR3 BGCR2 BGCR1 BGCR0 BGCRR
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value 0 0 0 0 1 1 1 1
0
0.5
1
1.5
-40 -20 0 20 40 60 80 10
0
Temperature [
o
C]
VREF [V]
Temperature range of interest
BGCRR is used to move the top of the VREF
curve to the center of the tempearture range of
interest.