LM3492, I can not understand where the error

Valeriy Chukalin

Prodigy 50 points

Other Parts Discussed in Thread: LM3492

It based on the reference circuit

XT1.1 - 12.5V or XT1.2 and pwm_control_dxo - 12.5V

VOUT - 22V

IC pin 15 - 12V

IC pin 16 - 8V

R5 And R6 - not installed

But between XT2.1 and XT2.3 or XT2.2 and XT2.3 -- 0V

Led strings stay off

over 7 years ago

0 Clinton Jensen over 7 years ago

TI__Mastermind 25500 points

Are those voltages being applied to the DIMx pins? If so that will damage the device. If not the device has been damaged some other way. They are way beyond the abs max specifications for those pins.

0 Valeriy Chukalin over 7 years ago in reply to Clinton Jensen

Prodigy 50 points

Thank you, missed the maximum ratings.
I will try to limit the DIM and replace IC

0 Valeriy Chukalin over 7 years ago in reply to Clinton Jensen

Prodigy 50 points

replaced lm3492
dim2 -4.4V
dim1 - 0V
Vin -12.5V
Vout - 22V

between XT2.1 and XT2.3 or XT2.2 and XT2.3 -- 0V

A simple circuit, I do not understand why do not work

0 Clinton Jensen over 7 years ago in reply to Valeriy Chukalin

TI__Mastermind 25500 points

I can't guarantee this is the issue without a lot more information, but you need to have a capacitor from VCC to ground. Do you have the LED loads connected when measuring the XT2 voltages? If that doesn't help could you get me a scope shot of the SW pins? Are you measuring 22V at Vout or is that what it is supposed to be when working correctly? What are your LED string voltages?

0 Valeriy Chukalin over 7 years ago in reply to Clinton Jensen

Prodigy 50 points

now, led string disconnected

Led string - 3.5V x10

Vout to gnd 22V

oscillogram from inductor (l1)

0 Valeriy Chukalin over 7 years ago in reply to Clinton Jensen

Prodigy 50 points

>>I can't guarantee this is the issue without a lot more information, but you need to have a capacitor from VCC to ground.
I install capacitor 1uF

it's WORKED !!!

I never occurred that the removal of this capacitor will break all,I think it is not necessary

Thank you so much !!!

0 Clinton Jensen over 7 years ago in reply to Valeriy Chukalin

TI__Mastermind 25500 points

You are welcome, I am glad it worked out. For future reference the VCC pin on a switching regulator is the output of an internal linear regulator that supplies power to all of the control circuitry and the FET gate driver. If there is no capacitor it will collapse as soon as there is a sudden current surge, the like FET turning on. So it is always important to have a capacitor to provide the current and keep VCC up. Good luck and let me know if you have any further questions.

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LM3492, I can not understand where the error