I am doing a project of dual power input and single output, with max load current 30A. The 1st input is 24V from ACDC supply, and 2nd input is battery with voltage around 23V to 28V.
In our case, fixed DC input has higher priority, when DC input is lost, battery will supply the load. When DC input is within 24V +- 1V tolorence, the battery will not supply the load.
Based on LTC4416, it is similar to "V1 less than V2" mode, but in low batt case, V1 could be higher than V2.
Currently there are 2 design options:
E1 is set at 1.35V when V1 is 24V (R divider by V1), and E2_N is set at 1.25V when V1 is 24V (R divider by V1). This means When V1 is <22.2V, E1 is < 1.25V.
E1 is pull up to V1 permanently, and E2_N is set at 1.35V when V1 is 24V (R divider by V1). That means when V1 is <22.2V, E2_N is < 1.25V.
Option A is from my colleague, but I am thinking it will operate like the following:
a) When 22.2V < V1 < 24V, E1 > 1.25V (High) and E2_N< 1.25V (Low), that mean both paths are ON, i.e. load sharing mode.
b) When V1 > 24V, E1 > 1.25V (High) and E2_N > 1.25V (High), so path 1 is ON and path 2 is OFF.
c) When V1< 22.2V, E1 < 1.25V (Low) and E2_N < 1.25V (Low), so path 1 is OFF and path 2 is ON.
That means case a) is not function as power prioritizer.
For Option B (follow “V1 less than V2” mode), V1 is always power the load except it is lower than allowed operating voltage (24V+-1). When V1 is >22.2V, E2_N is > 1.25V so path 2 is OFF. When the external AC power is lost and V1 drops below 22.2V, E2_N is < 1.25V so path 2 is ON.
What is your opinion and comment?
And I find LTC4418 power prioritizer is also possible for our case, but I am not sure if I choose external P-FET that is ok for 30A continuous operation, whether it is ok for LTC4418 to operate as expected.
If I use 2 exactly the same LTC4416 circuit and connect input and output in parallel respectively, in order to reduce the curent passing through the FETs, is there anything I need to take note?
Hi RF, Please note that E1 and E2# thresholds vary from 1.18V to 1.24V and may not match each other. Hence, option A may have more sharing than you expect. Since V1 is always enabled in option B, it will power the load even if it is lower than 22.2V in case the battery is lower than V1 (which may be okay). If you want to block V1 when it is low, you'll have to use back-to-back PFETs on that path and disable the path through E1. Therefore, the PFET power path is similar to LTC4418. Advantage with LTC4418 is that it will only keep one path on at a time, i.e., there is no sharing.
If you want to use N-channel FETs, which might be better for 30Amps, consider the LTC4359 ideal diode controller. You'll need two LTC4359, one per supply. Enabling/disabling the back-to-back MOSFETs can be achieved through its SHDN# pin.
Hi, so for LTC4416 the 2 power path have no direct on off logic relationship inside the IC, but only depending each comparator output logic, correct?
In both options, we are using back to back PFET for both paths. I think there is no harm to use back to back way on both paths but just extra component, is it?
For LTC4418, there is a short switchover time but LTC4416 doesn't have, right?
NFET is better for higher current application, is it because of lower Rds(on)?
Your understanding is correct. LTC4416 switchover will depend on enable comparator and when output is below input by Vfr (10 to 40mV).
And do you think there is possibility that the FET or IC damaged during operation except ESD or input overvoltage? The PFET we plan to use is around 100A, and max load current is 30A.
Or another way is to use 1 LTC4416 circuit but just double the no of PFET (2x back to back in parallel for V1 and 2x back to back in parallel for V2, 8x FETs in total) for current sharing in each path. Which one is better?