LM5008AEVAL: why the input voltage can't exceed 75V?

Howard Zou

Genius 12365 points

Part Number: LM5008AEVAL

Hi,

in the EVM, we emphasize not to exceed 75V for input voltage, but I can't find what limit the voltage level?

My customer would like to test with input voltage from 10V to 85V.

over 5 years ago

0 Iven Su over 5 years ago

TI__Expert 8245 points

Hi,

The current limit function limits the maximum input voltage, you can find a detailed info on 7.3.6 of its datasheet. If you want to apply a higher Vin, at least you should change R2 to a higher value or lower frequency by changing R1.

0 Howard Zou over 5 years ago in reply to Iven Su

TI__Genius 12365 points

Iven,

I've calculated the on time and off time by the procedure below:

in datasheet 7.3.5 equation 4.

when input voltage =90V,

Ton=0.43us.

Since output=5V, duty cycle D=5/90. When operating in a steady state, the off time Toff= 0.43/D-0.43=7.31us.

Toff determined by the current limit is determined by 7.3.6 equation (5).

Toff(current limit)= 11.97us. which is longer than Toff above.

So I should be okay to operate with input voltage =90V with the original parameters, right?

0 Iven Su over 5 years ago in reply to Howard Zou

TI__Expert 8245 points

Hi,

Please check the section 6 on the EVM users' guide, there are some tolerance and detection time consideration when designing the EVM. Thanks.

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LM5008AEVAL: why the input voltage can't exceed 75V?