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DRV10974
User Manual
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Texas instruments DRV10974 User Manual

User's Guide
SLOU505–April 2018

DRV10974 Tuning Guide

This tuning guide covers quick tuning and comprehensive tuning. The quick tuning section covers how to get the motor running quickly by inferring usable resistor values for the current, lead angle, and acceleration profile. The comprehensive tuning section covers the methodology for tuning each resistor value experimentally.
Contents
1 Bench Set Up................................................................................................................. 2
2 Quick Tuning ................................................................................................................. 2
3 Comprehensive Tuning ..................................................................................................... 2
3.1 Finding Closed-Loop Current and Coasting Time .............................................................. 3
3.2 Selecting CS Resistor.............................................................................................. 3
3.3 Selecting ADV Resistor............................................................................................ 4
3.4 Selecting RMP Resistor............................................................................................ 5
3.5 Example CS, ADV, and RMP Resistor Tuning ................................................................. 6
List of Figures
1 Example Peak Current in Closed Loop ................................................................................... 7
2 Example Coasting Time .................................................................................................... 7
3 Example Unsuccessful Steady-State, Stop, Start Test ................................................................. 9
4 Example Successful Steady-State, Stop, Start Test .................................................................... 9
List of Tables
1 Recommended Application Range for DRV10974 ...................................................................... 2
2 CS Resistor Table ........................................................................................................... 4
3 ADV Resistor Table ......................................................................................................... 4
4 RMP Resistor Values for t
5 RMP Resistor Table......................................................................................................... 6
6 Experimental Supply Current, Speed, and Speed/Current Ratio With Different Lead Times...................... 8
.............................................................................................. 5
coast
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DRV10974 Tuning Guide
1
Bench Set Up

1 Bench Set Up

Before connecting a motor, read the Quick Start Guide section of the DRV10974 Evaluation Module
User's Guide. This will help set up the proper connections for the DRV10974 and DRV10974EVM.

2 Quick Tuning

The goal of quick tuning is to get the motor running quickly by inferring usable resistor values for the current (CS pin), lead time (ADV pin), and acceleration profile (RMP pin).
If no information is known about the motor, the recommended the resistors should be as shown. Note that these resistors are the default installed on the DRV10974EVM:
• RCS= 115 kΩ – This sets the current limit to 1.4 A which is the second largest current limit.
• R
• R
If the motor fails to start up, reduce the CS value by one value, in accordance with the resistor selection in
Table 2, and repeat until the motor successfully starts up. The comprehensive resistor selection tables for
CS, ADV, and RMP are found in Table 2, Table 3, and Table 5, respectively. If the user knows the target supply voltage (VCC) used in the application and the resistance of the motor,
either from the motor data sheet or by measuring the resistance between two phases (R starting CS resistor value from Equation 2.
Using the current gathered from ICS, an appropriate RCScan be selected using Table 2. If motor performance is satisfactory (for example, runs at target maximum and minimum speeds, succeeds
on start and stop tests, meets start up time requirements, and starts up reliably) then no further tuning is needed. If the motor will not successfully start up, review Table 1 to make sure the motor is within the application specifications that the DRV10974 can drive. In addition, use the comprehensive tuning section to improve driving performance.
= 59 kΩ
ADV
– This sets the lead time to 400 µs, which is a lead time in the middle of the range of possible
settings.
= 7.32 kΩ
RMP
– This sets the second-order acceleration coefficient, the first-order acceleration coefficient, the
closed-loop acceleration and the closed-loop deceleration to 0.22 Hz/s2, 4.6 Hz/s, 2.7 s, and 44 s, respectively.
– This is the slowest acceleration ramp rate.
PH-PH
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), obtain a
Table 1. Recommended Application Range for DRV10974
Parameter Description MIN TYP MAX Unit
Motor Voltage - 4.4 12 18 V BEMF Constant (Kt) Phase to center tap. Measured while motor is coasting 5 150 mV/Hz Motor Phase
Resistance Motor Winding
Current Absolute Maximum
Current
Phase to center Tap. Can be derived from dividing phase-to-phase resistance by two.
During locked condition 2.5 A (Peak)

3 Comprehensive Tuning

The comprehensive tuning section covers the methodology for tuning each resistor value experimentally. As a result, testing is required to find the optimal resistor value for the motor. This includes replacing the resistors on the DRV10974 pins, as necessary. As a result, using a DRV10974EVM is highly recommend for easily replacing resistors on the pins. For more information, see the DRV10974 Evaluation Module
User's Guide.
2
DRV10974 Tuning Guide
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1 20 Ω
1 A (RMS)
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3.1 Finding Closed-Loop Current and Coasting Time

To choose the correct resistor values, the Closed-Loop Current (I found.
1. Set ADV to 400 µs (59 kΩ), CS to 1.4 A (115 kΩ), RMP to the slowest setting (7.32 kΩ) which is mentioned in the previous section. Note these are the default values on the EVM.
NOTE: If the user knows the target supply voltage (VCC) used in the application and the resistance of
the motor, either from the motor data sheet or by measuring the resistance between two phases (R
), a starting CS resistor value can be obtained from Table 2 and Equation 2.
PH-PH
2. Apply power to the device to spin the motor to the maximum target speed.
3. If the motor fails to spin up reduce the current limit (CS) by one level. Repeat step 3 until the motor successfully spins up.
4. Record the motor peak phase current during steady-state run (I
• This is used to determine the resistor on the CS pin
5. Provide a command of 0 and measure how long the motor takes to coast to a stop (t
• This is used to determine the resistor on the RMP pin

3.2 Selecting CS Resistor

The CS resistor controls the current limit during the open loop and align phase. Assuming I captured in the previous section, use the closest value derived from Equation 1 to find an acceptable CS resistor to set I
LIMIT
:
) and Coasting Time (t
PEAK
).
PEAK
Comprehensive Tuning
) must be
coast
).
coast
was
PEAK
(1)
NOTE: Large resistance motors may result in large I
values (that is, I
LIMIT
values that are larger
LIMIT
than in Table 2). As a result, use Equation 2 instead.
If the user knows the target supply voltage (VCC) used in the application and the resistance of the motor, either from the motor data sheet or by measuring the resistance between two phases (R
), obtain an
PH-PH
accurate CS resistor value from Equation 2:
(2)
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DRV10974 Tuning Guide
3
Comprehensive Tuning
Using the current gathered from ICS, select an appropriate RCSusing Table 2.
If the target RPM is slow, or the resistor given is larger than the value experimentally found in Section 3.1, then the CS may have to be reduced until the motor can start up successfully.

3.3 Selecting ADV Resistor

The ADV pin controls the lead time that the DRV10974 will start driving the motor. The lead time attempts to align the current applied through motor phases and the Back EMF voltage (BEMF) induced by the permanent magnets on the rotor passing by the windings on the stator. If the current and the BEMF are perfectly aligned, efficiency and start-up reliability are drastically increased.
However, tuning the lead time is very experimental and methodical. If the motor starts up reliability and reaches the target RPM at 100%, then optimal tuning may not be needed.
To tune the lead time, start with the default lead time (400 µs) then:
Table 2. CS Resistor Table
R
(kΩ) I
(CS)
7.32 200
16.2 400
25.5 600
38.3 800
54.9 1000
80.6 1200 115 1400 182 1600 (1500 during align and startup)
(LIMIT)
(mA)
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1. Successfully run the motor at 100% speed
2. Record the current consumed by the power supply (ICC)
3. Record the frequency on the FG pin (fFG) which corresponds to the speed
4. Next, calculate the ratio of frequency (speed) over current (fFG/ ICC) The highest ratio of frequency over current with the highest speed is the most efficient lead time. As a
result, decrease the lead time by one step (that is, lead time = 250 µs) by changing the ADV resistor and repeat the process.
• If the ratio gets larger with the same speed after decreasing the lead time – Keep decreasing the lead time until the ratio gets smaller
• If the ratio gets smaller with the same speed after decreasing the lead time – Increase the lead time instead and see if the ratio gets larger
• If the speed significantly gets smaller after making the lead time larger – Check previous values.
• Most applications fall within the 100 µs–400 µs range but the ratio and speed will show the best lead time
• Once ADV is tuned for a specific motor, it does not need to be tuned again
Table 3. ADV Resistor Table
R
(kΩ) Lead Time (µs)
ADV
10.7 10
14.3 25
17.8 50
22.1 100 28 150
4
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