SA303 Datasheet, PDF (12/14 Pages) Cirrus Logic – 3 Phase Switching Amplifier

SA303
Product Innova tionFrom
The current limit feature may be disabled
by tying the I_LIM/DIS1 pin to GND. The
current sense pins will continue to provide
top FET output current information.
Typically, the current sense pins source
current into grounded resistors which pro-
vide voltages to the current limit compara-
tors. If instead the current limit resistors
are connected to a voltage output DAC,
the current limit can be controlled dynami-
cally from the system controller. This tech-
nique essentially reduces the current limit
threshold voltage to (Vth-VDAC). During
expected conditions of high torque de-
mand, such as start-up or reversal, the
DAC can adjust the current limit dynami-
cally to allow periods of high current. In
normal operation when low current is ex-
pected, the DAC output voltage can in-
crease, reducing the current limit setting
to provide more conservative fault protec-
tion.
Figure 8. Current Limit Waveforms
A_t INPUT
V_th
Ia
OUTA
I_LIM/DIS1
2.6 EXTERNAL FLYBACK
DIODES
External fly-back diodes will offer superior reverse recovery character-
istics and lower forward voltage drop than the internal back-body di-
odes. In high current applications, external flyback diodes can reduce
power dissipation and heating during commutation of the motor current.
Reverse recovery time and capacitance are the most important param-
eters to consider when selecting these diodes. Ultra-fast rectifiers offer
better reverse recovery time and Schottky diodes typically have low
capacitance. Individual application requirements will be the guide when
determining the need for these diodes and for selecting the component
which is most suitable.
Figure 9. Schottky
Diodes
V_S V_S V_S
SA303
OUTA
OUTB
OUTC
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SA303U