tle8242 Infineon Technologies Corporation, tle8242 Datasheet - Page 29

• Manufacturer Part Number: tle8242
• Description: 8 Channel Fixed Frequency Constant Current Control With Current Profile Detection
• Manufacturer: Infineon Technologies Corporation

5.6
The average current over each PWM cycle is measured resulting in a 13 bit value. The summation of the 13 bit
values for all PWM periods in a dither period can be read by accessing SPI message #13. Also, the 11 MSb’s of
the minimum and maximum 13 bit values within a dither period can be read by accessing SPI message #12.
Average Current Over Dither Period
When the SPI message #13 is read or written, the 13 bit average current value for each PWM cycle within the
dither period is summed beginning with the positive going zero crossing of the dither waveform. The resulting 20
bit value represents the average current over the dither cycle as shown in equation:
If dither is disabled (Dither Steps = 0 or Dither Amplitude = 0), then the Average Current Feedback value will be
updated every PWM period and will be the same as the 13 bit current feedback value used in the PI controller.(1)
The SPI message #13 includes a VALID bit that indicates whether the average current measurement has
completed since the last register access. When the register is accessed, the VALID bit is cleared. The VALID bit
is set again when the summation is completed and new data has been stored in the register.
The summation process runs continuously on the last selected channel. So if the same channel is repeatedly
selected, new data is always available within one dither period after the SPI register is accessed.
If the selected channel is different than the previously selected channel, the summation process does not begin
until the beginning of the next dither period. So, new data may not be available until two dither cycles have
completed.
The channel selection for the Average Dither Current Feedback Message message will also select the channel for
the Minimum and Maximum Current Over Dither Period function.
Minimum and Maximum Current Over Dither Period
When the SPI message #12 is read or written, the 13 bit average current value for each PWM cycle within the
dither period is monitored beginning with the positive going zero crossing of the dither waveform. The most
significant 11 bits of the minimum and the maximum average current values are stored.
If dither is disabled (Dither Steps = 0 or Dither Amplitude = 0), then the Minimum and Maximum values will be
updated every PWM period and will be the 11 Msb’s of the 13 bit current feedback value used in the PI controller.
The SPI message #12 includes a VALID bit that indicates whether a dither period has completed since the last
register access. When the register is accessed, the VALID bit is cleared. The VALID bit is set again when the dither
period is completed and new data has been stored in the minimum and maximum registers.
The minimum and maximum detection process runs continuously on the last selected channel. So, if the same
channel is repeatedly selected, new data is always available within one dither period after the SPI register is
accessed.
If the selected channel is different than the previously selected channel, the detection process does not begin until
the beginning of the next dither period. So, new data may not be available until two dither cycles have completed.
The channel selection for the Minimum and Maximum Current Over Dither Period message will also select the
channel for the Average Dither Current Feedback function.
Data Sheet
Current Feedback Registers
Dither
Current
Feedback
[
mA
]
=
29
Functional Description and Electrical Characteristics
Avg Dither
2
15
∗
Dither
Current
Steps
∗
Rsense
320
[
mV
[
Ohm
Rev. 1.0, 2009-02-25
]
]
TLE8242