Calculating an adjustable PWM for TLE9853QX H-Bridge Output

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RLGeorge
Level 3
Level 3
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Firmware’s intent is to close the bi-directional output of the H-Bridge with a PWM to limit in-rush from the load.  

Starting with a short on time, increasing the on time every 1mS.

After increasing the on-time 100 times for a total of 100mS the PWM is disable and the output is 100%.

Monitoring the LED with the scope tracking the 1 mS transitions through the firmware the output does not begin to PWM until about 60 mS after it is expected.

Is the shadow register not being transferred correctly?

Please see attached documents with details.

Schematic is very similar to TLE9855 Eval Board.

Thank you for your help.

 

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Raj_C
Moderator
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Hi @RLGeorge 

We find that time scale of sampling time is too high. Please observe the signal in the edge-trigger mode. When the duty cycle is very low the oscilloscope may not capture the signals.

 

Please let us know if this helps.

 

Thank you

Best regards

Raj Chaudhari

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5 Replies
Raj_C
Moderator
Moderator
Moderator
500 replies posted 50 likes received 250 replies posted

Hi @RLGeorge 

We find that time scale of sampling time is too high. Please observe the signal in the edge-trigger mode. When the duty cycle is very low the oscilloscope may not capture the signals.

 

Please let us know if this helps.

 

Thank you

Best regards

Raj Chaudhari

RLGeorge
Level 3
Level 3
10 likes given 10 questions asked 25 sign-ins

Thank I was able to make some adjustments to extend my total PWM time.  Is there a document that defines in laymen terms what limitations there may be if any?

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Raj_C
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Hi @RLGeorge,

There is no document regarding this topic.

Thank you

Best Regards

Raj Chaudhari

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RLGeorge
Level 3
Level 3
10 likes given 10 questions asked 25 sign-ins

One last question. Since the resolution of my scope does not allow me to confirm. Is the value loaded in the shadow transfer in hertz?

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Raj_C
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Hi @RLGeorge,

A special shadow transfer signal (T12_ST) can be generated to facilitate updating the period and compare values of the compare channels CC60, CC61, and CC62 synchronously to the operation of T12.
A T12 shadow register transfer takes place (T12_ST active):
• while timer T12 is not running (T12R = 0), or
• STE12 = 1 and a Period-Match is detected while counting up, or
• STE12 = 1 and a One-Match is detected while counting down
When signal T12_ST is active, a shadow register transfer is triggered with the next cycle of the T12 clock.

For additional information please refer to the 18.3.6 T12 Shadow Register Transfer of TLE985x UM.

Thank you

Best Regards

Raj Chaudhari

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