at90pwm81-16se ATMEL Corporation, at90pwm81-16se Datasheet - Page 191

• Manufacturer Part Number: at90pwm81-16se
• Description: 8-bit Avr Microcontroller With 8k Bytes In- System Programmable Flash
• Manufacturer: ATMEL Corporation

16.3.2
7734M–AVR–03/10
BGCRR – Bandgap Calibration Resistor Register
Read/Write
Initial Value
• 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 5 mV.
Updating the BGCC bits will affect the BOD detection level. The BOD will react quickly to the new
detection level.
Bit
Read/Write
Initial Value
• 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.
Vbg as a function of temperature. Vbg has a positive temperature coefficient at low temperatures and neg-
ative 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.
-
-
0
7
-
-
0
-
-
0
6
-
-
0
-
-
0
5
-
-
0
-
-
0
4
-
-
0
BGCC3
R/W
1
3
BGCR3
R/W
1
BGCC2
R/W
0
2
BGCR2
R/W
0
BGCC1
R/W
0
1
BGCR1
R/W
0
AT90PWM81
Figure 16-2
BGCC0
R/W
0
0
BGCR0
R/W
0
BGCCR
BGCRR
illustrates
191