TPS61170: Inductor selection on Figure 20. 48-V Phantom Power Application Circuit

Hirotaka Matsumoto

Part Number: TPS61170

Hi all

Would you mind if we ask TPS61170?

On the datasheet Figure 20. 48-V Phantom Power Application Circuit, the inductor is 22uH.
Could you give us the formula for the inductor?
We would like to calculate the optimum value of the inductor.

The customer's condition is as folllows;

<The customer's condition>
Vin=4V～10V
Vout=48V/10mA

Kind regards,

Hirotaka Matsumoto

over 7 years ago

0 Helen chen over 7 years ago

TI__Mastermind 40080 points

Hi Hirotaka-San，

This is a charge-pump circuit. So for the 48V output case, you can calculated based on 24V/20mA output, then use the boost inductor formula to calculate the inductor. Use Vin=4V, and use 80% efficiency during calculation. K_ripple is the inductor ripple, generally it is around 20%-40%, but since the output current is small, this value can be much higher than 40% at light load condition, 50%-100% is also OK. So you can get 22uH inductance with the following formula. (Vs=Vo=24V, Iout=20mA, ɧ=0.8)

0 Hirotaka Matsumoto over 7 years ago in reply to Helen chen

Guru 27585 points

Helen san

Thank you so much for your reply!

K_ripple is the inductor ripple, generally it is around 20%-40%,
->We would like to confirm K_ripple just in case.
   Which is correct?
   - Iout × 0.2-0.4
   - Just value 0.2-0.4

Kind regards,

Hirotaka Matsumoto

0 Helen chen over 7 years ago in reply to Hirotaka Matsumoto

TI__Mastermind 40080 points

Hi Hirotaka-San

K_ripple means (0.2-0.4) at heavy load condition， or a >0.4 value （may as big as 1） at light load application. it is a number, no need to multiply current。

In your application, the output current is very small, so you can use a bigger K, it can even be near 1. if K=0.8, then the inductor value is just around 22uH.

0 Hirotaka Matsumoto over 7 years ago in reply to Helen chen

Guru 27585 points

Helen san

Thank you so much for your reply always!

OK, we got about charge-pump circuit configuration.

On the other hand, we have additional question "Figure 22. 12-V to 48-V Flyback Topology".
Could you share us the formula for the inductance L ?
As the back ground of this question, the customer would like to configure 48V Phantom Power with smaller size.

Charge-pump configuration : L is small, however schottky barrier rectifier D1 to D3 are a little big.
Flyback configuration : It depends on L(transformer).

We appreciate your help always.

Kind regards,

Hirotaka Matsumoto

0 Helen chen over 7 years ago in reply to Hirotaka Matsumoto

TI__Mastermind 40080 points

Hi Hirotaka-San,

Since this is a very old part. I don't know how the original designer calculate the transformer.So I'll recalculate it. It need some time, please wait in patient.

0 Hirotaka Matsumoto over 7 years ago in reply to Helen chen

Guru 27585 points

Helen san

Thank you so much for your help.

We are waiting for your reply.

Kind regards,

Hirotaka Matsumoto

0 Helen chen over 7 years ago in reply to Hirotaka Matsumoto

TI__Mastermind 40080 points

Hi Hirotaka-San,

Let's discuss offline. :)

0 Hirotaka Matsumoto over 7 years ago in reply to Helen chen

Guru 27585 points

Helen san

Thank you for you update!
We accepted your request!

Kind regards,

Hirotaka Matsumoto

0 Helen chen over 7 years ago in reply to Hirotaka Matsumoto

TI__Mastermind 40080 points

Hirotaka-San,

OK, thanks! Then I'll close this post.

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TPS61170: Inductor selection on Figure 20. 48-V Phantom Power Application Circuit