STR750-MCKIT STMicroelectronics, STR750-MCKIT Datasheet - Page 7

• Manufacturer Part Number: STR750-MCKIT
• Description: Power Management Modules & Development Tools Compete motr control starter kit
• Manufacturer: STMicroelectronics
• Type: Motor / Motion Controllers & Driversr

Specifications of STR750-MCKIT

• Input Voltage: 18 V to 35 V
• Product: Power Management Modules
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

UM0379
3.2
Single-shunt current reading configuration
In the single-shunt current reading configuration, the current sampling is done only when the
value on the shunt resistor is positive.
The only positive value read on the shunt resistor allows to set a higher gain for the op-amp
than the one set in three-shunt mode. However, because the input of the op-amp is not rail-
to-rail, in this configuration also, it is necessary to polarize the it to compensate for this
limitation.
Figure 5
Figure 5.
The op-amp is used in follower mode with a gain set by resistors r and R.
The relation between the input signal e and the signal v on the positive input of the follower
is:
with:
The resistor values implemented on the MB549B board are:
and
Therefore, the gain is:
G = s/v = (R + r)/r
v = ((U*h)/(k*r4) + f(e))
k =(1/r3+1/(r1+r2)+1/r4)
h=r1/ (r1 +r2)
f(e)=(e*r2)/ (r1 + r2) + (e*r1)/((k*(r1+r2)*(r1+r2))
R=11000Ω \ r=1000Ω \ r1=1130Ω \ r2=1000Ω \ r3=22Ω \ r4=2200Ω
U=5V
G = 12
shunt
shows the op-amp configuration used in single-shunt configuration.
Single-shunt configuration
e
U
r4
i2
r1
w
i1
r3
r2
Operational amplifier configuration
v
r
3
2
+5V
+
-
R
6
s
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