DRV8881: Vtrip on Figure9 and the chopping current

Hirotaka Matsumoto

Part Number: DRV8881

Hi all

Would you mind if we ask DRV8881E?

We have some question which is relation to follow forum;
e2e.ti.com/.../2967335

On the forum, "Figure 9 xISEN Full-Scale Trip Voltage value is below formula 1 result. I would think the figure 9 value is the typical value."

Could you refer to the attachment file?
20190528_DRV8881E.pdf
On this attachment file, we assume that follows;
-Vtrip=500mV : Vref=3.40～3.45V
-Vtrip=250mV : Vref=3.5V

So, it is not satisfied with follows;

In case of formula(2), Electrical Characteristics is fitable with Vtrip condition.
However, formula(2) is not equal to Figure9.

So, we would like to calculate the current chopping correctly.

Kind regards,

Hirotaka Matsumoto

over 6 years ago

0 Hirotaka Matsumoto over 6 years ago

Guru 27585 points

In relation to our post, we add the follows;

8666.20190528_DRV8881E_Current.pdf

Kind regards,

Hirotaka Matsumoto

0 Hirotaka Matsumoto over 6 years ago

Guru 27585 points

Hi all

We guess that your days are so busy, however could you give us the comment ASAP?
If you need the time, when will you reply for it?

Kind regards,

Hirotaka Matsumoto

0 Wang5577 over 6 years ago in reply to Hirotaka Matsumoto

TI__Guru 56650 points

Matsumoto-san,

Yes. We are busy right now. But, e2e support always our key support. I missed the post in the beginning.

First, Av in the spec table is not ideal 6.6.
2nd, the spec table number is the official number. Specially, it has min/max number with it. In this case, use AV spec table number and min/max value to estimate the Itrip. The Figure 9 gives additional info. Such as: linear curve, offset idea at lower current setting.

0 Hirotaka Matsumoto over 6 years ago in reply to Wang5577

Guru 27585 points

Wang5577 san

Thank you so much for your reply.
We would like to understand your mention correctly.

First, Av in the spec table is not ideal 6.6.
->Does it mean which show "AV Amplifier attenuation" on the datasheet P8?
   Does it mean that there is the difference 6.6(formula(2)) and 6.58(typ)?

In this case, use AV spec table number and min/max value to estimate the Itrip.
->Does it mean which we should consider min/max value to estimate the Itrip?

The Figure 9 gives additional info such as: linear curve, offset idea at lower current setting.
->You mentioned "Figure 9 xISEN Full-Scale Trip Voltage value is below formula 1(typo 2) result." on another post.
    We got that Figure 9 contains additional info such as: linear curve, offset idea at lower current setting.
    Therefore, does it mean Figure 9 xISEN Full-Scale Trip Voltage value is not below formula(2) correctly?
    Compared with using formula (2), there is the differece 40mA. Does it mean which this difference contains additional info such as: linear curve, offset idea at lower current setting?
    In case of AV=min/max, tolerance will be ±10%. Otherwise, in this case, is additional info(linear curve, offset idea at lower current setting) dominant?

As the conclusion,
Should we calculate Itrip using formula(2)?
Is Figure9 not suitable for Itrip calculation?

As the backgroud of this question, the customer would like to know calculate the current correctly.

We appreciate your help always.

Kind regards,

Hirotaka Matsumoto

0 Wang5577 over 6 years ago in reply to Hirotaka Matsumoto

TI__Guru 56650 points

Matsumoto-san,

->Does it mean which show "AV Amplifier attenuation" on the datasheet P8? Yes.
Does it mean that there is the difference 6.6(formula(2)) and 6.58(typ)? Yes.
->Does it mean which we should consider min/max value to estimate the Itrip? Yes.
->does it mean Figure 9 xISEN Full-Scale Trip Voltage value is not below formula(2) correctly? I would think Figure 9 and P8 spec will match at 3.3Vref.
-> Does it mean which this difference contains additional info such as: linear curve, offset idea at lower current setting?
If there is any conflict, please use P8 spec table number as reference. Also, when you do the calculation, please use 3.3V REF.

Use As the conclusion,
->Should we calculate Itrip using formula(2)? Yes for 3.3V VREF.
->Is Figure9 not suitable for Itrip calculation? It is for the estimation if VREF is not 3.3V.

If I do the calculation for the Itrip with different VREF value, I will get two points first:
a. Itrip value from formula(2) with 3.3V VREF
b. VREF or Itrip Offset from Figure 9
And then, use a linear equation to estimate the Itrip value from VREF offset pin to 3.3V VREF.

0 Hirotaka Matsumoto over 6 years ago in reply to Wang5577

Guru 27585 points

Hi Wang5577 san

Thank you so much for your support always!

->Should we calculate Itrip using formula(2)? Yes for 3.3V VREF.
->Is Figure9 not suitable for Itrip calculation? It is for the estimation if VREF is not 3.3V.
If I do the calculation for the Itrip with different VREF value, I will get two points first:
a. Itrip value from formula(2) with 3.3V VREF
b. VREF or Itrip Offset from Figure 9
And then, use a linear equation to estimate the Itrip value from VREF offset pin to 3.3V VREF.

We would like to confirm several points finally.

<Additional question1>
When the customer uses without VREF=3.3V(For example : 2.7V or 2.0V or 0.5V),
-Formula is not suitable for current regulation calculation correctly.
-We should consider Figure9 to estimate current regulation calculation and then we use a linear equation to estimate the Itrip value from VREF offset pin to 3.3V VREF.
Is our recognition correct?

<Additional question2>
Do you have any formula to estimate the correct Itrip in case of lower VREF(For example : 2.7V or 2.0V or 0.5V)?

<Additional question3>
We got that there is the difference between Figure9 and formula (2).
And then, we got that Figure9 contains linear curve and offset idea at lower current setting.
So, what do you indicate "linear curve and offset idea at lower current setting" concretely?

We appreciate your help always.
So, we are waiting for your reply.

Kind regards,

Hirotaka Matsumoto

0 Hirotaka Matsumoto over 6 years ago in reply to Wang5577

Guru 27585 points

Hi Wang5577 san

We think that your days are so busy, however if you have some advice, could you give us the reply?

Kind regards,

Hirotaka Matsumoto

0 Wang5577 over 6 years ago in reply to Hirotaka Matsumoto

TI__Guru 56650 points

Matsumoto-san,

<Additional question1>
When the customer uses without VREF=3.3V(For example : 2.7V or 2.0V or 0.5V),
-Formula is not suitable for current regulation calculation correctly.
-We should consider Figure9 to estimate current regulation calculation and then we use a linear equation to estimate the Itrip value from VREF offset pin to 3.3V VREF.
Is our recognition correct?

Yes.

<Additional question2>
Do you have any formula to estimate the correct Itrip in case of lower VREF(For example : 2.7V or 2.0V or 0.5V)?

If I do the calculation for the Itrip with different VREF value, I will get two points first:
a. Itrip value from formula(2) with 3.3V VREF
b. VREF or Itrip Offset from Figure 9
And then, use a linear equation to estimate the Itrip value from VREF offset pin to 3.3V VREF.

<Additional question3>
We got that there is the difference between Figure9 and formula (2).
And then, we got that Figure9 contains linear curve and offset idea at lower current setting.
So, what do you indicate "linear curve and offset idea at lower current setting" concretely?

What is the Figure 9 error at 3.3VREF? Is it in AV tolerance range? Formula 2 only gives one point data at 3.3V VREF in the spec table. If you want to estimate 2V VREF Itrip, how do you draw a line to match Figure 9 with that one point data? Here is my answer:

Regards,

Wang Li

Motor drivers

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DRV8881: Vtrip on Figure9 and the chopping current