LT8391 does not Start

Question

Hello, 
 We've built 4 prototypes with 2 LT8391 stages. I've come across one that will not start, I've noticed the SS pin is a sawtooth (see waveform below). 
 All input pins are appropriate levels: EN=5V, CTRL1,2=2V, PWM=5V, SYNCH=CLK (392KHz) - Also INTVCC=5V and VREF=2V. 
 
 The circuit is similar to the Evaluation Kit: 
 www.analog.com/.../DC2345A-5-SCH.PDF 
 Does anyone have any insight? 
 Edit: I neglected to also mention, there are no measured shorts in the FETs and LED output.

ntenorio · Accepted Answer

Hi Iain-Trakka , 
 In my understanding only 1 out of 4 prototypes has this problem. You mare try to inspeact visually the board including the components. And also, as part of initial debugging, you may check each pin connection if good by having diode-checking from gnd (positive probe) to each pin and compare it to the readings of the good boards as reference. This will give you hint of a poor contact or connection, possible short or faulty component. 
 Thanks, 
 Noel)

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LT8391 does not Start