# Inquiry Regarding Capacitor Specifications and Bootstrap Capacitor Calculation for IR2109(4)(S) Datasheet

## Inquiry Regarding Capacitor Specifications and Bootstrap Capacitor Calculation for IR2109(4)(S) Datasheet

Level 1
Level 1

I hope this message finds you well. I am reaching out regarding a couple of questions I have about the datasheet for the IR2109(4)(S).

Firstly, I am curious about the capacitor specifications mentioned in the datasheet. I noticed that polarized capacitors are recommended for certain applications. However, I am interested in exploring the possibility of using non-polarized capacitors instead. Could you kindly provide some insight into whether non-polarized capacitors can be safely substituted for the polarized ones mentioned in the datasheet?

Secondly, upon attempting to calculate the value of the bootstrap capacitor using the provided formula, I encountered an unexpected result. Specifically, when I substituted the given values into the formula, I found that the denominator resulted in a negative value: (Vcc - Vf - VLs - Vmin) = (12V - 1V - 2.35V - 9V) = -0.35V. This negative value raises some concerns and prompts me to seek guidance on how to proceed with determining the appropriate value for the bootstrap capacitor. Could you please provide clarification on whether a negative value in this context is valid, or if there might be an alternative method or consideration to account for in this calculation?

I understand the importance of adhering to recommended component specifications and calculations, but I am curious about any potential flexibility or alternative approaches in these matters. Any guidance or clarification you could offer on these issues would be greatly appreciated.

Thank you very much for your attention to these inquiries. I look forward to hearing from you soon.

Best regards,

1 Solution

## Re: Inquiry Regarding Capacitor Specifications and Bootstrap Capacitor Calculation for IR2109(4)(S) Datasheet

Moderator
Moderator

Hello,

Please go through below link to know more  how to use the bootstrap capacitor formula.

https://www.infineon.com/dgdl/Infineon-Using_Monolithic_Voltage_Gate_Drivers-AN-v01_00-EN.pdf?fileId...

Same formula is used here also, however, on page no. 2 under section "Considerations about bootstrap" , the worst condition will be when load current (Io<0) .As  per this, the Vmin. is zero and then capacitor voltage  will be function of  Vcc, Vf and Vceon. when you consider these parameters, you will not get negative value.

Thanks and regards,

AZIZ

6 Replies

## Re: Inquiry Regarding Capacitor Specifications and Bootstrap Capacitor Calculation for IR2109(4)(S) Datasheet

Moderator
Moderator

Hello,

1) For point 1, may I know which capacitance you are talking about. Is it bootstrap capacitance?

2) Please find then link below to calculate the bootstrap capacitor value.

https://www.irf.com/technical-info/designtp/dt98-2.pdf

Thanks and regards,

AZIZ

## Re: Inquiry Regarding Capacitor Specifications and Bootstrap Capacitor Calculation for IR2109(4)(S) Datasheet

Level 1
Level 1

Thank you for providing the link to calculate the bootstrap capacitor value. I appreciate your assistance.

I've previously utilized this link for calculating the bootstrap capacitor value. However, I encountered an unexpected result during the calculation process. Specifically, when I input the relevant values into the formula, namely (Vcc - Vf - VLs - Vmin) = (12V - 1V - 2.35V - 9V) = -0.35V, I obtained a negative result.

Could you kindly advise on how to interpret this negative value or if there might be an alternative approach or consideration to ensure an accurate calculation?

Thank you for your attention to this matter. I look forward to your guidance.

## Re: Inquiry Regarding Capacitor Specifications and Bootstrap Capacitor Calculation for IR2109(4)(S) Datasheet

Moderator
Moderator

Hello,

Could you please verify how you are getting the Vmin. as 9V. and Vls= 2.35V.

Thanks and regards,

AZIZ

## Re: Inquiry Regarding Capacitor Specifications and Bootstrap Capacitor Calculation for IR2109(4)(S) Datasheet

Level 1
Level 1

To clarify, Vls (VCE(sat)) refers to the saturation voltage of the IGBT "SKM 100GB128D" as specified in its datasheet. Additionally, Vmin represents VBSUV- for the IR2109(4)(S) as indicated in its datasheet.

## Re: Inquiry Regarding Capacitor Specifications and Bootstrap Capacitor Calculation for IR2109(4)(S) Datasheet

Moderator
Moderator

Hello,

Please go through below link to know more  how to use the bootstrap capacitor formula.

https://www.infineon.com/dgdl/Infineon-Using_Monolithic_Voltage_Gate_Drivers-AN-v01_00-EN.pdf?fileId...

Same formula is used here also, however, on page no. 2 under section "Considerations about bootstrap" , the worst condition will be when load current (Io<0) .As  per this, the Vmin. is zero and then capacitor voltage  will be function of  Vcc, Vf and Vceon. when you consider these parameters, you will not get negative value.

Thanks and regards,

AZIZ

## Re: Inquiry Regarding Capacitor Specifications and Bootstrap Capacitor Calculation for IR2109(4)(S) Datasheet

Moderator
Moderator

Hello,

Did you check the link. If you have doubts then please let me know.

Thanks and regards,

AZIZ