LM2695: LM2695

ephraim oved

Prodigy 40 points

Part Number: LM2695

Dear Sir.

I have some problem with the IC LM2695 , See attached PDF.

The input voltage is 24V ,

Some measurements .

Voltage on pin 9 is 7V , Output Voltage is 0.4V

What should be the voltage at pin 8 .

Please Advise PS.pdf PS.pdf

over 5 years ago

0 Arief Hernadi over 5 years ago

TI__Mastermind 23825 points

Hi,

I think you need some kind of ripple injection circuit such as shown on this EVM.
www.ti.com/.../snva147a.pdf

Also do you see any voltage on SS pin?

Thanks

0 ephraim oved over 5 years ago in reply to Arief Hernadi

Prodigy 40 points

Hi.

0 V on SS PIN.

0 Frank De Stasi over 5 years ago in reply to ephraim oved

TI__Guru 59335 points

The voltage on the SS pin should be at least a couple of volts, or so.
Since you have a VCC voltage, check that the SS cap is not shorted on the pin on the PCB is not shorted.

0 JohnTucker over 5 years ago in reply to ephraim oved

TI__Guru**** 191445 points

Ephraim,

There are at least two issues. As Arief noted, LM2695 is a constant on time hysteretic off time converter. It requires some ripple voltage at VFB, so it is made to use electrolytic capacitors. For your switching frequency and inductor, you would need about .66 ohms in series with C31. or else you will need to design the appropriate ripple injection circuit.

Second, you not the SS voltage at pin 7 is 0 V. At start up you should see a linear ramp up to about 2.5 V on the SS pin.

0 ephraim oved over 5 years ago in reply to JohnTucker

Prodigy 40 points

Hi.

You are correct , SS pin is shorted to gnd due to excessive solder.

Thanks

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LM2695: LM2695