AT90PWM81 Atmel Corporation, AT90PWM81 Datasheet - Page 110
AT90PWM81
Manufacturer Part Number
AT90PWM81
Description
Manufacturer
Atmel Corporation
Datasheet
1.AT90PWM161.pdf
(325 pages)
Specifications of AT90PWM81
Flash (kbytes)
8 Kbytes
Pin Count
20
Max. Operating Frequency
16 MHz
Cpu
8-bit AVR
Hardware Qtouch Acquisition
No
Max I/o Pins
20
Ext Interrupts
3
Usb Speed
No
Usb Interface
No
Spi
1
Graphic Lcd
No
Video Decoder
No
Camera Interface
No
Adc Channels
11
Adc Resolution (bits)
10
Adc Speed (ksps)
125
Analog Comparators
3
Resistive Touch Screen
No
Dac Channels
1
Dac Resolution (bits)
10
Temp. Sensor
Yes
Crypto Engine
No
Sram (kbytes)
0.25
Eeprom (bytes)
512
Self Program Memory
YES
Dram Memory
No
Nand Interface
No
Picopower
No
Temp. Range (deg C)
-40 to 125
I/o Supply Class
2.7 to 5.5
Operating Voltage (vcc)
2.7 to 5.5
Fpu
No
Mpu / Mmu
no / no
Timers
1
Output Compare Channels
8
Input Capture Channels
1
Pwm Channels
6
32khz Rtc
No
Calibrated Rc Oscillator
Yes
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12.7
110
Enhanced Resolution
AT90PWM81
Lamp Ballast applications need an enhanced resolution down to 50Hz. The method to improve the normal
resolution is based on Flank Width Modulation (also called Fractional Divider). Cycles are grouped into
frames of 16 cycles. Cycles are modulated by a sequence given by the fractional divider number. The
resulting output frequency is the average of the frequencies in the frame. The fractional divider (d) is
given by OCRnRB[15:12].
The PSC output period is directly equal to the PSCOUTn0 On Time + Dead Time (OT0+DT0) and
PSCOUTn1 On Time + Dead Time (OT1+DT1) values. These values are 12 bits numbers. The frequency
adjustment can only be done in steps like the dedicated counters. The step width is defined as the fre-
quency difference between two neighboring PSC frequencies.
It is possible to apply the Flank Width Modulation (FWM) on RB, RB+RA, SB, SB+SA. The selection is
done bit the bits PBFMn0 and PBFMn.
According to the ramp mode and the enhanced resolution mode (defined by PBFMn1:0), the frequency
difference Δf can take three different values:
with k is the number of CLK
with f
Example, in normal mode, with maximum operating frequency 160 kHz and f
The resulting resolution is Delta F equals 64MHz / 400 / 401 = 400 Hz.
In enhanced mode, the output frequency is the average of the frame formed by the 16 consecutive cycles.
f
Then the frequency resolution is divided by 16. In the example above, the resolution equals 25 Hz.
b1
and f
OP
b2
is the output operating frequency.
are two neighboring base frequencies.
PSC
Δf1
Δf2
period in a PSC cycle and is given by the following formula:
=
=
f
AVERAGE
f
f1 f2
f1 f2
AVERAGE
–
–
=
=
=
=
f
----------
f
----------
16 d
-------------- -
PSC
PSC
k
k
k
16 d
-------------- -
16
Δf
–
=
16
–
–
–
=
f
----------
f
×
----------- -
k
----------- -
k
PSC
f
f
OP
PSC
PSC
0
+
+
×
f
--------- -
PLL
k
1
2
f
b1
=
=
+
+
----- -
16
----- -
16
f
f
d
d
PSC
PSC
×
×
----------- -
k
f
f
×
×
b2
PLL
+
-------------------
k k
-------------------
k k
1
(
(
1
2
+
+
1
2
)
)
PLL
= 64 Mhz, k equals 400.
7734P–AVR–08/10
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