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LM3421 LED driver off-time calculation

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T

treez

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Hello,

Please could you advise on the operation of the LM3421 LED driver IC?

LM3421 datasheet:
https://www.ti.com/lit/ds/symlink/lm3421.pdf
(block diagram is on page 10)

1….Off time duration:
Is the off time duration simply the length of time that it takes the “CT” capacitor, connected to pin 5, “RCT”, to charge up from 0V to Vin/25 Volts?
(page 30 shows the “RCT” pin and buckboost connection.)
I presume that during the main FET ON time, the RCT pin is held at 0V by the internal FET inside the LM3421?

Also, is the error amplifier output (in the LM3421) frozen during pwm dimming off time intervals?....as you know, it shouLD be otherwise the error amp output unwantedly rails high during the no_current interval.
 

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