need check if buck circuit design correct -LTC3605AEUF

Hi Sir,

We recently designed a buck circuit with AD device LTC3605A, which is a 12V to 5V circuit.

We build 30pcs boards with two batches LTC3605A. (each batch LTC3605 build on 15pcs boards).

Let's call the two batches LTC305A as batch A and batch B.

For Batch A LTC3605 boards, the output is correct for all 15pcs boards.

For batch B LTC3605 boards, the output for some of the boards is not correct. For the defect boards, the output may be too low, say 4.8V, some of the board output is two high, which is about 6.0V.

For the output=6.0V board, we check the FB pin of LTC3605, which is about 0.7V (should be 0.6V+/-10%).

For one of the output =4.8V board, we disconnect ITH (Pin 6) of LTC3605 with the external resistor and capacitor (R1006, C1012, C1013), then connect this pin to IntVcc (pin 21), then the output is correct (5V at pin 11 of LTC3605)

We are now quite sure the soldering is not problem. So, the issue may be LTC3605 batch quality issue or design issue.

so, would you please help check if our design has any problem? especially the inductor, Cin, Cout selection, and Rc Cc1(resistor and capacitors at pin ITH)? thanks a lot.

designcircuit.docx