MAX25510 with SEPIC configuration does not start up with input voltage above certain value

Question

Hello! I have display backlight driver made up with MAX25510 IC in SEPIC configuration. The IC does not start up above certain value of input voltage. 
 The circuit is as follow. The PWM DIM input is at 200 Hz, and AIM is at 0V. Load is 4 parallel strings with 6 LED in series 480 mA of total current. 
 
 If input voltage is within ~21.5 V I can see successful start and operation. The startup process is shown in next picture. The yellow chanel is BSTMON input, and green is OUT_1 input. DC-DC rumped up to OUT_ regulation (19.6 V) and IC is operational in all designed ranges of input voltage (even if I rise it above 21.5V)

If the input voltage is above ~21.5V the IC does not start and I see the process as shown below. The converter turns off at certain voltage on BSTMON that depands on input voltage. It starts with 21.5 V input and 19.3V out shut off and ends with 30V input and 11.8V out shut off.

I have try to rise the switching frequency, double input inductor value, double couple capasitor value, increase or decrease output capacitance but with no any succsess. 
 
 What is the reason of such IC behavior? 
 
 Best Regards, 
 Evgeny

EPetrov312 · Accepted Answer

May the total voltage that sees internal switch be the reason of such behaviour? As per datasheet the abs max voltage at DRAIN pin is 40V. But in SEPIC configuration it will be Vin + Vout. So for my configuration it will exceed the abs raiting at exact 21.5 volts (19.5V regulated point + 21.5V input voltage > 40V)? It explains the trend that rising the input voltage tends to lowering shut off output voltage.)

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MAX25510 with SEPIC configuration does not start up with input voltage above certain value