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Application Notes — MC74113 & MC75113
Juno Step Motor Control IC User Guide
99
15
15.6 Drive-Related Safety and
Monitoring Features
This example shows the motor drive-related analog monitoring features. Please refer to
Low Motor Drive With Leg Current Sensing/Control”
for leg current sensing functions.
The block of R9, R10, R13 and C5 is for temperature sensing. R13 is a thermistor, and its resistance depends on the
temperature. MC74113 and MC75113 will sense the scaled voltage and convert it into temperature reading. C5 need
to be tied close to the Temperature pin to improve noise immunity.
In this example, it is assumed that the thermistor is away from the MC74113 and MC75113 and close to the power
train, which usually has the highest temperature. Accordingly, C5 is referred to the analog ground, and R13 to digital
ground. R10 is optional to improve the noise immunity. If R13 is close to the analog portion, Vcc can be AnalogVcc
instead and R13 be tied to the analog ground.
The block of R2, R3, R5 and C3 is for input voltage sensing. This voltage divider will scale the +HV into the range
between ground and 3.3V. In this example, it will scale 63V to 3.3V. C3 need to be tied close to BusVoltage pin. The
voltage divider is referenced to digital ground while C3 is to analog ground. An optional resistor can be put between
R5 and C3 to improve noise immunity as R10 does for temperature sensing function. This block is also a low-pass
filter with bandwidth of 1.5kHz. This bandwidth should be selected to respond to real voltage fault event while
attenuating bus noise.
U1 is the high side bus current sensing IC. With current sensing resistor R1 at 10mOhm, U1 has a current scaling
factor of (13.3/2*0.01)=66.5mV/A.
U2A is for short circuit protection. R12 and R7 set the protection trigger point, and R6 provides a hysteresis. When
Vcc is 3.3V, the trigger point is 1.65V with hysteresis. Brake will go to low and trigger protection when U1 output is
over 1.65V, which is (1.65/66.5mv/A)= 25A.
The output of U1 also goes to U3A, which is a peak-detection circuit. The analog input is sampled at 20kHz. The
peak-detection circuit will hold the maximum peak current reading between the sampling points so MC78113 can
detect the maximum current. The necessity of this peak-detection circuit depends on the power train design. For
example, if C1 and C2 have big enough capacitance so that the current in R1 will be close to DC, U3A can be a buffer
instead.
This peak detection circuit (U3A) is optional. If not used, the BusCurrentSupply pin has an internal comparator, and
this comparator can also detect overcurrent.
MC74113 and MC75113 supports leg current sensing with current loop control, and R11 and R15 are leg current
sensing resistors.