Other Parts Discussed in Thread: PMP31210, LM5119, LM5148, LM5146, LM5145
Hi, do you know why the LM5143 (Synch Buck controller) was used for this Synch Buck spec (PMP31210 ref design)
of 20-58vin and 13.5Vout and 50A out?...
PMP31210 Ref Design:
https://www.ti.com/tool/PMP31210
Surely they should have just used the same_priced LM5119 instead?
The LM5143 has a max gate drive voltage of just 4.5V, meaning they are restricted to logic level FETs and their Rds(on)
is much higher at the 80V rating needed.
The LM5119 has a gate drive voltage up to 15V...meaning far lower Rds(on) FETs are available , and so FETs would be much cheaper.
Unfortunately we dont have an official company address, and so cant ask on the ti.com forum.
You would think they would advertise products in their suitable useage case, rather than in a totally unsuitable case?
I mean, 58Vin Synch Buck, with 700W output, and they are using a gate drive of 4.5V When they could have gone with 12V gate drive for
same price solution.
Maybe the SMPS is operated in sub zero temperature buildings and the extra heat dissipation is useful? -only plausible explanation.
PMP31210 Ref Design:
https://www.ti.com/tool/PMP31210
LM5143:
https://www.ti.com/product/LM5143
LM5119:
https://www.ti.com/product/LM5119
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As you know, the only real reason to use logic level FETs in any SMPS is that your Vin is below say 7V, and you dont want to bother with a bias booster so you just put up with logic level FETs. As you know, people are not using logic level FETs because of any advantage of them. They have no advantages over "normal" threshold FETs. Especially in a synchronous buck, logic level FETs are a poor choice, because with their low gate threshold voltage, they may get spuriously turned ON by the other FET turning ON and pulsing a current spike through the drain gate capacitance. Hot logic level FETs have a ridiculously low VGS(th)......as you know, they are a very poor choice, and one that you "put up with".
Not least is the fact that if you choose a logic level gate driver, then you are restricted to only logic level FETs...so you likely end up paying more for your FETs, and being more susceptible to FET nil-stocking.
Also, how does a logic level hi side gate driver supply (bootstrapped) in a synch buck chip ever do "UVLO" of the driver?...as you know...it cant really do it......when VGSth is that low you cant really do it....if you have a 12V gate driver, then you can have it "UVLO out" at say 7V.
Logic-level devices, also, have higher gate charge than standard-level parts of similar V(BR)DSS and RDS(on)
