st7pmc2s6 STMicroelectronics, st7pmc2s6 Datasheet - Page 192

• Manufacturer Part Number: st7pmc2s6
• Description: 8-bit Mcu For Automotive With Nested Interrupts, Flash, 10-bit Adc, Brushless Motor Control, 5 Timers, Spi, Linsci?
• Manufacturer: STMicroelectronics

On-chip peripherals
192/371
Sensorless mode
This mode is used to detect BEMF zero crossing and end of demagnetization events.
The analog phase multiplexer connects the non-excited motor winding to an analog 100mV
hysteresis comparator referred to a selectable reference voltage.
IS[1:0] bits in MPHST register allow the input to be selected which drives to the comparator
(either MCIA, B or C). Be careful that the comparator is OFF until CKE and/or DAC bits are
set in MCRA register.
The VR[2:0] bits in the MCRC register select the reference voltage from seven internal
values depending on the noise level and the application voltage supply. The reference
voltage can also be set externally through the MCVREF pin when the VR[2:0] bits are set.
Table 83.
BEMF detections are performed during the measurement window, when the excited
windings are free-wheeling through the low side switches and diodes. At this stage the
common star connection voltage is near to ground voltage (instead of V
excited windings are powered) and the complete BEMF voltage is present on the non-
excited winding terminal, referred to the ground terminal.
The zero crossing sampling frequency is then defined, in current mode, by the
measurement window generator frequency (SA[3:0] bits in the MPRSR register) or, in
voltage mode, by the PWM generator frequency and phase U duty cycle.
During a short period after a phase commutation (C event), the winding where the back-emf
is read is no longer excited but needs a demagnetization phase during which the BEMF
cannot be read. A demagnetization current goes through the free-wheeling diodes and the
winding voltage is stuck at the high voltage or to the ground terminal. For this reason an ‘end
of demagnetization event’ D must be detected on the winding before the detector can sense
a BEMF zero crossing.
For the end-of-demagnetization detection, no special PWM configuration is needed; the
comparator sensing is done at a selectable frequency (f
So the three events C (commutation), D (demagnetization) and Z (BEMF zero crossing)
must always occur in this order in autoswitched mode when hard commutation is selected.
VR2
1
1
1
1
0
0
0
0
Threshold voltage setting
ST7MC1K2-Auto, ST7MC1K6-Auto, ST7MC2S4-Auto, ST7MC2S6-Auto
VR1
1
1
0
0
1
1
0
0
VR0
1
0
1
0
1
0
1
0
Threshold voltage set by external MCVREF pin
typical value for V
V
SCF
REF
) (see
voltage threshold
3.5V
2.5V
1.5V
0.6V
0.2V
2V
1V
Table
DD
DD
166).
= 5V
/2 when the