A problem with iraudamp7s

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lixia
Level 2
Level 2
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Hello, I have a question to consult R17 (47k) in the circuit diagram on page 30 of this file iraudamp7s

1, what is the role?

2, Is it a starting resistor? How it works?

3, if it is a starting resistor, how to calculate the value of this resistor? Is it related to +B?

4, Is it related to "CSH"? If there is a relationship, how do I calculate it?

1.png2.png

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1 Solution
Liz
Employee
Employee
10 replies posted 10 likes given 25 sign-ins

Hi Lixia,

Good questions!

1,2,Pre-charge for start up

3, Yes, it relates to +B voltage. The calculation is to satisfy your minimum start-up bus voltage and have certain current through the resistor.

4, No.

Please let me know if you have further questions.

Liz

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8 Replies
Liz
Employee
Employee
10 replies posted 10 likes given 25 sign-ins

Hi Lixia,

Good questions!

1,2,Pre-charge for start up

3, Yes, it relates to +B voltage. The calculation is to satisfy your minimum start-up bus voltage and have certain current through the resistor.

4, No.

Please let me know if you have further questions.

Liz

lixia
Level 2
Level 2
25 sign-ins 10 replies posted First like received

Hi Liz,

Thank you so much!

10-15mA?

1、If the supply voltage is ±75V, how to calculate R17?

2、According to Table 5, the current flowing through R17 does not appear to be 10-15mA?

3、Is this explained in the datasheet?

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Liz
Employee
Employee
10 replies posted 10 likes given 25 sign-ins

Hi Lixia,

The pre-charge current requirement is slightly different between each product. Sorry to misguide you in the previous answer.

Normally, the pre-charge resistor can handle a wide range of bus voltage, the 33k can work between +/-25V to +/-50V bus voltage without a problem. The rough calculation for IRS2092 is Bus voltage times 1000, so 75*1000=75k.We would recommend you use 75k for R17. If the minimum bus voltage is lower, please use the lowest bus voltage of the end product. 

Thanks,

Liz

lixia
Level 2
Level 2
25 sign-ins 10 replies posted First like received

Hi Liz,

Thank you so much!

1、Is there any documentation that explains this?

2、there is another question is how to calculate the power consumed by the R17 resistor?

3、Is it related to the IQBS in the figure below? (Datasheet for irs2092)How is it calculated?

121.png

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Liz
Employee
Employee
10 replies posted 10 likes given 25 sign-ins

Hi Lixia,

It is nice to discuss this topic here, since I have exactly same question few years ago.

1, No

2, Not critical, since it is only for start up, regular 0805 or 0603 can handle it if follow previous calculation recommendation.

3 Not related.

Thanks,

Liz

 

 

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lixia
Level 2
Level 2
25 sign-ins 10 replies posted First like received

Hi Liz,

Thank you so much!

About this resistance power issue.

Help me see the path of the current flowing through R17, right?

1、When the low-side mosfet is turned on, the voltage across R17 is 2VB, and the instantaneous power is still very large.

2、When the high-side mosfet is turned on, the voltage across R17 is VB-VCC (VCC is the bootstrap voltage) Is there any problem with my analysis?

3、How to calculate R17 power consumption?

x1.pngx2.png

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Liz
Employee
Employee
10 replies posted 10 likes given 25 sign-ins

Hi Lixia,

Thank you for bring the topic.

1, When the low-side MOSFET is turned on, the voltage across R17 is 2*V(+B)-Vcc, the instantaneous power is high and power consumption correlates to duty.

2、When the high-side MOSFETs is turned on, the voltage @VB =V(+B)+Vcc due to VS=V(+B), the voltage across R17 is VCC

3, The average power consumption mainly depends on the input signal/duty of low-side MOSFET is turned on. It might can use simulation for music signal, or use sinuous signal(roughly 50% of low-side on).

In +/-75V case, ((75*2-12)^2 / 75000)*0.5=0.127W, if you want to put extra design margin on top of that, 1/4W would be a better option.

Best regards,

Liz

lixia
Level 2
Level 2
25 sign-ins 10 replies posted First like received

Got it, thank you very much.👍😀