Rainbow Electronics ATtiny861_V - Manual (Page 98)

98
2588B–AVR–11/06
ATtiny261/461/861
16.5 Dead Time Generator
The Dead Time Generator is provided for the Timer/Counter1 PWM output pairs to allow driving
external power control switches safely. The Dead Time Generator is a separate block that can
be used to insert dead times (non-overlapping times) for the Timer/Counter1 complementary
output pairs OC1x and OC1x when the PWM mode is enabled and the COM1x1:0 bits are set to
“01”. The sharing of tasks is as follows: the Waveform Generator generates the Waveform Out-
put (OCW1x) and the Dead Time Generator generates the non-overlapping PWM output pair
from the Waveform Output. Three Dead Time Generators are provided, one for each PWM out-
put. The non-overlap time is adjustable and the PWM output and it’s complementary output are
adjusted separately, and independently for both PWM outputs.
Figure 16-6. Output Compare Unit, Block Diagram
The Dead Time Generation is based on the 4-bit down counters that count the dead time, as
shown in
Figure 16-7 . There is a dedicated prescaler in front of the Dead Time Generator that
can divide the Timer/Counter1 clock (PCK or CK) by 1, 2, 4 or 8. This provides for large range of
dead times that can be generated. The prescaler is controlled by two control bits DTPS11..10.
The block has also a rising and falling edge detector that is used to start the dead time counting
period. Depending on the edge, one of the transitions on the rising edges, OC1x or OC1x is
delayed until the counter has counted to zero. The comparator is used to compare the counter
with zero and stop the dead time insertion when zero has been reached. The counter is loaded
with a 4-bit DT1H or DT1L value from DT1 I/O register, depending on the edge of the Waveform
Output (OCW1x) when the dead time insertion is started. The Output Compare Output are
delayed by one timer clock cycle at minimum from the Waveform Output when the Dead Time is
adjusted to zero. The outputs OC1x and OC1x are inverted, if the PWM Inversion Mode bit
PWM1X is set. This will also cause both outputs to be high during the dead time.
Figure 16-7. Dead Time Generator
OCnx
pin
WGM10
Waveform Generator
top
FOCn
COMnx
bottom
PWMnx
OCWnx
Dead Time Generator
OCnx
pin
DTnH DTnL DTPSn
CK OR PCK
CLOCK
OCnx
OCnx
CLOCK CONTROL
OCnx
OCnx
CK OR PCK
CLOCK
OCWnx
4-BIT COUNTER
COMPARATOR
DTnL DTnH
DEAD TIME
PRE-SCALER
DTPSn
DTn I/O REGISTER
DATA BUS (8-bit)
TCCRnB REGISTER
PWM1X
PWM1X