AN4370
Application note
L99ASC03 PMBLDC sensorless 3-phase motor driver
G. Celeste; G.Maimone
Introduction
The L99ASC03 is a 3-phase BLDC driver IC. The device can drive six external MOSFETs in
BLDC drive systems and detect back EMF zero-crossing events, thus allowing sensorless
rotor position detection.
This application note is intended to provide guidance to users on specific application-related
topics.
March 2014
DocID025336 Rev 1
1/23
www.st.com
Contents
AN4370
Contents
1
2
3
4
5
6
7
8
9
10
11
12
BEMF Zero crossing detection internal peripheral . . . . . . . . . . . . . . . . 5
Flashing an external microcontroller . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Quick mother startup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Diagnostic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Watchdog . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Unused pins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
PRE-DRIVE tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Estimating power dissipation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Calculation example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
CSA and OC comparator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
External components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
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List of tables
List of tables
Table 1.
Table 2.
Table 3.
Table 4.
PWM edge used for filtering the selected BEMF Z crossing comparator output . . . . . . . . . 6
Unused pins connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
PRE-DRIVE tests summary table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
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List of figures
AN4370
List of figures
Figure 1.
Figure 2.
Figure 3.
Figure 4.
Figure 5.
Figure 6.
Figure 7.
Figure 8.
Figure 9.
Figure 10.
Figure 11.
BEMFIP block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
BEMF detection stepping of BEMFCNT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Ringing noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
BEMFCNT update event. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
SPI command frame structure (SDI). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
PRE-DRIVE tests functional block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
PRE-DRIVE test example: Phase 1 disconnected . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
PRE-DRIVE test example: Phase 1 connected . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Difference between charge pump output voltage and input supply voltage vs. input supply
voltage V
VS
as a function of charge pump load (C
CP1
= C
CP2
= 220 nF, C
TANK
= 1 µF) . . 16
Supply current at VS pin vs. input supply voltage V
VS
as a function of charge pump load
(C
CP1
= C
CP2
= 220 nF, C
TANK
= 1 µF) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Reverse battery current flow through the device . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
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BEMF Zero crossing detection internal peripheral
1
BEMF Zero crossing detection internal peripheral
Designed to achieve the six step driving mode, the BEMFIP is based on a 6 step counter
(BEMFCNT bits) which selects, according to
Figure 2,
the floating phase sent to the input of
three comparators in order to detect its BEMF Z crossing event. Of course we will select just
one of the 3 comparator outputs through the BEMFMOD bit and sample it. The PWM
sampling signal will be the one of the input channel (either ILx or IHx) chosen by the
combinations of the following bits: BEMFCNT, BEMFSW, BEMFMOD & BEMFPOL (the
sampling signal could be the driving PMW at the HSides, or the driving PWM at the LSides,
or the active freewheeling PWM at the LSides, or the active freewheeling PWM at the
HSides), whereas the PMW sampling edge will depend upon the combinations of the
BEMFMOD & BEMFPOL bits. Even though everything seems a bit tricky, almost everything
is done automatically by the BEMF IP state machine itself.
Figure 1. BEMFIP block diagram
For instance, according to
Figure 2,
for BEMCNT = 1 the floating phase sent to the
comparators will always be phase #3, namely the motor terminal connected to SH3 pin, and
the PWM sampling signal will be either IH1 or IL1. With the PWM on the HS MOSFETs
(BEMFSW = 0) and BEMFMOD = 1, selecting the BUS/2 comparator output, the PMW input
signal used to sample the output of the BUS/2 comparator will be IH1, whereas with the
PWM on the LS MOSFETs (BEMFSW = 1) and BEMFMOD = 1, the PMW input signal used
to sample the output of the BUS/2 comparator (BEMFMOD = 1) will be, this time, IL1.
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