Dear sirs,
I made a demo board to test LM5642 buck converter according to AN-1292 LM5642 Evaluation Board. , but the ic not work . I was configured the ic as dual-phase, single output regulator , but the converter not work. even without load the ic is at shutdown mode. I was checked the hardware many times but I was not find the reason that the ic is at sleep mode. VIN is 12V , VLIN5 is ok ,5.0V , VDD1,2 ok 5.0V. ..onSS1, onSS2 (pins 9,10 ) are at 1.12V, but I can't understand why , cause at those pins (tied together ) is connected only a cap. 22nf . According to data sheet, pins 9, 10 are pulled high internally....there is no reason to remain at low level after soft start....what are possible reasons for that , and what can I check to enable operation of ic ?