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Priority configuration

Category: Hardware
Product Number: LTC4418


I would like to develop a circuit using the LTC4418/4421 that includes 2 sources, when there is a priority between primary and secondary. If the primary enters the UV, I would like to switch to the secondary and not go back, even if the primary passed the UV threshold and is considered normal. Does one of this components allow this? Perhaps a two-component CAS would allow this? I would appreciate recommendations

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  • I’m doing something similar with the LTC4418. When the primary or secondary hits the UV threshold, I want to latch the fault so that supply can’t be used again until it is physically disconnected from the system. Using this as added security to protect against potential motorboating from Li-ion batteries with high internal impedance in case the set hysteresis level isn’t adequate in some cases. Connect an NFET to the UV pin for the primary channel, and drive it with a D flip-flop clocked by the VALID1 signal (VALID1 should be pulled up to the primary input). Tie the input of the flip flop high. For the flip-flop reset signal, pull it up high but also connect an NFET to it to ground and drive that NFET with an RC delay. So when you plug in your primary input, the flip flop will startup in reset (output LOW) for the RC delay time, then whenever your primary input trips your UV setting, the rising edge from VALID1 going HI will clock the flip flop and cause it to output a HI signal to the NFET which will ground the UV pin and latch it low. This permanently forces a UV fault. Only way to clear it is to physically disconnect the primary input from the system.