RAA210040 | what will happen when the device loses synchronization during operation?

Question

Hello Team, 
 I am promoting The RAA210040 to customer who had serval projects. 
 The question from the engineer is regarding the external synchronization of this module. 
 What happens when the device loses synchronization during operation and what is the likelihood that it will occur? 
 Waiting for your kind feedback, thanks a lot. 
 
 KR, 
 Shai

AB_RENESAS · Accepted Answer

Hi, 
 If customer use SYNC pin, it should be notes that using an external SYNC frequency within &plusmn;25% of the switching frequency set by the FS pin. 
 To avoid big change of operational frequency in the event of a loss of synchronization. We have instructions on DS as below. 
 
 And our die has an internal 1M&Omega; pull-down resistor to prevent an undefined logic state in case of SYNC pin float. 
 This means that if the SYNC signal is lost, the module will switch to PFM mode and the frequency will change to the switching frequency set by the FS pin at higher load. 
 The attachment are some waveforms under steady state , with different SYNC frequency and FS resistors. SYNC has higher priority but should avoid the situation that SYNC is pull down and fs resistor is floating. 
 
 And we have some compare test for SYNC switching process and find two issues: 
 
 iout=4A, Vin=5V, Vout=2.5V, SYNC 1Mhz change to pull-down, FS floating. 
 
 Cause to hiccup mode after SYNC pull-down, Vout is not stable. So, FS cannot float.

Iout=0.5A, Vin=5V, Vout=2.5V, SYNC 2Mhz change to pull-down, FS resistor to 200kohm(1Mhz). 
 
 Vout ripple is big if frequency change obviously at the time of SYNC ON and SYNC OFF. Recommend the external SYNC frequency within &plusmn;25% of the switching frequency set by the FS pin. 
 
 Thanks 
 AB

AB_RENESAS · Answer

Hi Shai, 
 As per recommendation external SYNC frequency should be within &plusmn;25% of the switching frequency set by the FS . So It will work properly/ not loses the synchronization. 
 Thanks 
 AB

RAA210040 | what will happen when the device loses synchronization during operation?

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