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AN4158 Datasheet(PDF) 29 Page - STMicroelectronics

No. de pieza AN4158
Descripción Electrónicos  Peak current control with automatic decay adjustment
PDF  34 Pages
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Fabricante Electrónico  STMICROELECTRONICS [STMicroelectronics]
Página de inicio  http://www.st.com
Logo STMICROELECTRONICS - STMicroelectronics

AN4158 Datasheet(HTML) 29 Page - STMicroelectronics

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AN4158
Setup and optimization
34
Figure 24. On-time measurement
In order to obtain the lowest current ripple possible, the TON_MIN value should be slightly
longer than the commutation time. Using longer TON_MIN increases the current ripple but
forces a higher minimum duty cycle value increasing the robustness of the control system.
5.1.2
TOFF
The off-time of the control system sets the maximum PWM frequency of the control system
fSW,max (minimum on-time violation events excluded), as described in Equation 11.
Equation 11
In general, motors having a lower LPh/RPh ratio (weak inductive motor) require higher
control frequencies and then lower TOFF values. On the contrary, higher TOFF values and
then lower control frequencies may be needed when the LPh/RPh ratio is higher (strong
inductive motor).
5.1.3
TOFF_FAST
The maximum fast decay duration should be set taking into account that its value is directly
proportional to the ripple of the current control algorithm.
High current ripple increases the noise, causes higher power dissipation and reduces the
positioning precision in microstepping operation. In general, the current ripple should be as
low as possible.
The minimum fast decay, which is one-eighth of TOFF_FAST, must be longer than
TON_MIN to avoid subsequent minimum on-time violations (see Figure 25).
V
BUS
OFF
ON
V
BUS
OFF
OFF
V
BUS
ON
OFF
V
BUS
ON
OFF
Power bridge
driving signal
t
on
Low side
High side
turn-on time
turn-
Dead time
Blanking time
Current sensing disabled
Commutation time
Current sensing
enabled
Even if the reference current is reached
the system cannot detect this condition
until the end of commutation
Reference current reached
AM15126v1
fSW,max
1/ tON_MIN tOFF
+

=



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