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dttworld
dttworld
Associate II
June 6, 2012
Question

EVAL6470H Application

  • June 6, 2012
  • 4 replies
  • 898 views
Posted on June 06, 2012 at 22:38

Hi,

I'm currently evaluating the L6470 for a mobile robot application using the EVAL6470H demo boards. I've been able to get my differential drive motors running and now I want to perform 2 tests to mimic real world scenarios. Please tell me if the following two scenarios would cause damage to the chip and possibly a way to protect against it:

1) During motor operation an external ESTOP switch on the robot kills input power (8-45v terminal) to the board

2) With the battery power removed from the EVAL boards, the stepper motors are back driven. I'm seeing a voltage appear at the 8-45V input of the board during back driving because the motor is acting as a generator. VDD of +5V may or may not be present. This is a common scenario since end users have a tendency to push the robot during transportation or an ESTOP from scenario 1.

Thank you
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4 replies

dttworld
dttworldAuthor
Associate II
June 13, 2012
Posted on June 13, 2012 at 20:25

Could someone from ST please kindly answer these questions?

Thank you

Enrico Poli
Enrico Poli
ST Employee
June 18, 2012
Posted on June 18, 2012 at 10:06

Hello,

I'm really sorry for the waiting.

Both the scenarios shouldn't cause any issue to the application operation. Removing the supply current during operation cause the the UVLO protection triggering, so the device is forced in safe state (power bridges disabled) and then it is turned off.

In case the BEMF of the motor supplies the device, it turns on in safe state. The presence of the VDD supply voltage is not a problem, but in this case we suggest to pull-up the STBY input using the internal VREG.

Kind Regards

Enrico

dttworld
dttworldAuthor
Associate II
June 19, 2012
Posted on June 19, 2012 at 22:32

Enrico,

Thanks for the answers.

I'm noticing that my EVAL6470H boards are going into thermal shutdown running at 27 volts and 3 amps peak. I am microstepping at 1/128 mode and turning at only 100 steps/second. Chip parameters were set using the BEMF compensation from the dSPIN evaluation software. All waveforms have been verified with an oscilloscope and current probe. There's no way this eval board could handle 3 amps RMS if it is over heating at just 3 amps peak.

Question 1: Do these test results seem normal?

Question 2: When will the EVAL6470PD be available?

Question 3: Can you provide contact info so I can get some samples of the L6470 in the PowerSO package?

Thank you

Enrico Poli
Enrico Poli
ST Employee
June 21, 2012
Posted on June 21, 2012 at 17:21

Hi,

The current capability of the device is not limited by the absolute ratings only, but by the power dissipation also.

For example, a load current of 3Ar.m.s. on both the phases implies a power dissipation of:

P = 4 x RdsON x I^2 = 4 x 0.37 x 3^2 = 13.3 W

(0.37 is the average RdsON value between HS and LS of the device)

using our EVAL6470H with a  Rthja of 21°C/W this dissipation results in a temperature increase in the IC of 21 x 13.3 = 279 °C

The thermal inertia of the system allows driving such high powers for a short time, but in steady state the power dissipation cannot be withstood by the application.

Using a EVAL6470PD the temperature increase in the IC should be 12 x 13.3 = 160 °C.

In this case the thermal inertia is higher and it allows driving these currents for a longer time (maybe seconds), but steady state is still not possible.

Both boards and samples should be shortly available on ST website.

Enrico

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