• State Resolved
  • Locked Locked
  • Replies 1 reply
  • Subscribers 64 subscribers
  • Views 228 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LM3409: EN rise to PGATE fall spec inquiry

Howard Zou
Genius 12365 points
Part Number: LM3409

Hi,

my customer uses LM3409 and find that the spec in the datasheet doesn't meet what they see in the board.

In datasheet 7.5 Electrical Characteristics EN pin rising delay is 42ns.

But they observed 100us delay. 

  • 0
    TI__Intellectual 2590 points

    Howard,

    Likely the VCC regulator has discharged and the part is "off".  The EN pin to PGATE delay is only accurate if VCC has charged above VCC UVLO (3.73V typical...and remember this voltage is relative to VIN).  If VCC is below that value, it has discharged too far and needs to charge back up to VCC UVLO before all ciruits are active and the delay  to PGATE is minimized.

    I have seen this question before when people use the EN pin for very low frequency dimming or flash functions.  This was designed to operate above 100Hz for PWM dimming in which case VCC will not fall to below the threshold in normal operation.

    If  you have a lower frequency and/or very long off-time (like a flash application) then you can use the UVLO pin for PWM dimming instead.  It only disables and enables the PGATE.  All other circuits remain active.

    -JP