Datasheet

191
7734Q–AVR–02/12
AT90PWM81/161
• Bit 7:4 – Res: Reserved Bit
This bit is reserved for future use.
• Bit 3:0 – BGCC3:0: 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, so the lowest value for Vbg is reached when BGCC3:0 is 0000 and the
maximum value when BGCC3:0 is 1111. The step size is approximately 5mV.
Updating the BGCC bits will affect the BOD detection level. The BOD will react quickly to the
new detection level.
15.3.2 BGCRR – Bandgap Calibration Resistor Register
• Bit 7:4 – Res: Reserved Bit
This bit is reserved for future use.
• Bit 3:0 – BGCR3:0: BG Calibration of Resistor ladder
These bits are used for temperature gradient adjustment of the bandgap reference. Figure 15-2
on page 192 illustrates Vbg as a function of temperature. Vbg has a positive temperature coeffi-
cient at low temperatures and negative temperature coefficient at high temperatures. Depending
on the process variations, the top of the Vbg 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 5 possible settings: 0000, 0001, 0011, 0111, 1111. The value
0000 shifts the top of the Vbg curve to the highest possible temperature, and the value 1111
shifts the top of the Vbg curve to the lowest possible temperature.
Bit 7 6543210
- - - - BGCR3 BGCR2 BGCR1 BGCR0 BGCRR
Read/Write - - - - R/W R/W R/W R/W
Initial Value 0 0 0 0 1 0 0 0