TLE82452-3SA_15 Datasheet, PDF (29/71 Pages) Infineon Technologies AG – 2 Channel High-Side and Low-Side Linear Solenoid Driver IC

TLE82452-3SA
Current Control
8.6
PWM Frequency Controller
The integrated PWM Frequency controller regulates the PWM Frequency using an “Integral” control loop with a
programmable gain, KI. This control loop monitors the actual PWM period and compares it to the PWM period
setting in the PWM Period Register. The error in the PWM period is multiplied by the gain KI and then integrated
at each PWM cycle. The output of the controller adjusts the “on time” of the PWM signal until the actual PWM
period matches the programmed PWM period.
KI gains of 1, 1/2, 1/4, 1/8, 1/16, 1/32, and 1/64 can be selected in the PWM Period Register. The KI value of 1,
KI_index =0, has the fastest response time, the KI value of 1/64, KI_index=6, has the slowest response time, but
with less overshoot and less ringing. KI_index = 6 is the recommended setting for initial evaluation.
8.7
Autozero
Each channel has an autozero function which measures and compensates for the offset of analog current
measurement circuits. The autozero function is automatically initiated during power-up after the first write to the
CLK-DIVIDER register, or with a reset “RESN” after the first write to the CLK-DIVIDER register. The function can
also be initiated by the user by setting the AZ start bit in the AUTOZERO SPI message. The EN bit in the
SETPOINT register must be set to 0 to initiate the auto-zero function. This AZ START bit is automatically cleared
by the device when the autozero sequence is complete. The measured offset of current measurement circuits can
be read by the micro controller via the SPI message AUTOZERO. Autozero functions with the EN pin in the high
or low state.
Care must be taken if the device enters Autozero while current is flowing in the solenoid. This can occur if the
device is reset or the Autozero bit is set, while current is flowing in the solenoids. The current will create an
unintended offset. During initialization or if a reset occurs during operation the device should be held in reset until
the current decays to zero. During normal operation an Autozero should not be initiated until the solenoid current
decays to zero. The time is determined by the inductance of the solenoid, which can be calculated or measured.
8.8
Measurement Functions
The SPI register FEEDBACK can be read to access the value of the load current measured by the device and the
value of the output PWM period. The CFB bit in the DITHER register selects between two measurement types.
When CFB=0, the average current and the switching period are measured over each switching cycle. When
CFB=1, the maximum current and minimum currents are measured over a dither cycle. Also the number of
switching cycles occurring in the last dither cycle is measured.
When the CFB bit = 0 and the device is not in calibration mode, the FEEDBACK register contains a 12 bit Current
Feedback field. The content of this field represents the integration of the load current measured by the analog
current measurement circuit blocks over the most recent switching period. The average load current can be
calculated according to the equation I_load_avg = 1.5* Current Measurement_Feedback / Period Measurement
Feedback.
When the CFB bit = 0 and the device is not in calibration mode, the actual output frequency of each channel can
be determined by reading the 12 bit Period Feedback field in the FEEDBACK register. This field contains the
number of system clocks (Fsys) counted during the most recently completed PWM period divided by 16, this is the
same resolution as the PWM set register.
When the CFB bit = 1 and the device is not in calibration mode, the FEEDBACK register contains two 8 bit Current
Feedback (CFB) fields. The contents of these fields represent the minimum and maximum load current measured
by the analog current measurement circuit blocks over the most recent dither cycle when dither is enabled.
Otherwise, these fields contain the minimum and maximum load current values since the last read of the
FEEDBACK register. I min and I max = 1.5* readout / 127.
When the CFB bit = 1 and the device is not in calibration mode, the FEEDBACK register contains an 8 bit field
which contains the number of full switching cycles in the last dither cycle. This information can be used by the
Data Sheet
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Rev 1.0, 2015-03-27