LTC2952 with incorrect push button

Karlson on Oct 18, 2021

Dear EZ,

I use LTC2952 in configuration B in many my circuits and it works flawlessly.

Now I have a task to create a prioritized power path controller not with a push button but with a rotary switch with "make before break" functionality. Due to some circuit restrictions I can't use a one shot pulse generator to create a valid push button event when a rotary switch changes its position from OFF to ON and vice versa (let's assume that in ON position switch can only pull down to ground and in OFF position it goes Hi-Z). I've modeled a case where device is turned on via a PB pin going low and I shut down the device via applying a zero to !KILL input when an external MCU detects that switch was turned to OFF position. I don't need !INT at all.

So my question is: is it ok to leave a PB pin low for an infinite time? Any drawbacks or surprises?

Grammar mistake
[edited by: Karlson at 6:34 PM (GMT -4) on 25 Oct 2021]

Top Replies

Ashapiro
Oct 25, 2021 +1 verified
Karlson said:
So my question is: is it ok to leave a PB pin low for an infinite time? Any drawbacks or surprises?

There shouldn't be any surprises. PB# acts on a falling edge, which doesn't happen if it…

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+1 Ashapiro

on Oct 25, 2021 6:28 PM
Karlson said:
So my question is: is it ok to leave a PB pin low for an infinite time? Any drawbacks or surprises?

There shouldn't be any surprises. PB# acts on a falling edge, which doesn't happen if it is held low.
Out of curiosity, what config are you using? (A,B,C, or D)
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0 Karlson on Oct 25, 2021 6:33 PM in reply to Ashapiro

As I mentioned:

Karlson said:
I use LTC2952 in configuration B
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0 Ashapiro

on Oct 25, 2021 6:33 PM in reply to Karlson
Sorry, glazed over that detail.

Maybe take your circuit for a spin in LTspice to see if it works like you think it does.
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0 Karlson on Oct 25, 2021 6:43 PM in reply to Ashapiro

Ashapiro said:
Maybe take your circuit for a spin in LTspice to see if it works like you think it does.

Already done and I think everything works fine, but I tried to simulate 2952 some time ago in some exotic configuration and model did not behave as a real part did, that's why I ask my question.

Here is my current .asc:

Version 4
SHEET 1 3612 1076
WIRE 320 -576 256 -576
WIRE 64 -512 0 -512
WIRE 560 -464 128 -464
WIRE 0 -432 -16 -432
WIRE 320 -432 320 -576
WIRE 320 -432 272 -432
WIRE 64 -416 64 -512
WIRE 64 -416 0 -416
WIRE -112 -352 -144 -352
WIRE -16 -352 -16 -432
WIRE 0 -352 0 -416
WIRE 128 -352 128 -464
WIRE 128 -352 96 -352
WIRE 160 -352 128 -352
WIRE 256 -352 256 -496
WIRE 272 -352 272 -432
WIRE 384 -352 368 -352
WIRE -32 -240 -32 -304
WIRE 16 -240 16 -304
WIRE 16 -240 -32 -240
WIRE 64 -240 16 -240
WIRE 240 -240 240 -304
WIRE 240 -240 192 -240
WIRE 288 -240 288 -304
WIRE 288 -240 240 -240
WIRE 560 -208 560 -464
WIRE 1088 -208 560 -208
WIRE 1200 -208 1088 -208
WIRE 1328 -208 1200 -208
WIRE 1440 -208 1328 -208
WIRE 1520 -208 1440 -208
WIRE 1328 -192 1328 -208
WIRE 1088 -176 1088 -208
WIRE 1440 -176 1440 -208
WIRE 1520 -176 1520 -208
WIRE 384 -160 384 -352
WIRE 384 -160 -336 -160
WIRE 1200 -128 1200 -208
WIRE 1088 -80 1088 -112
WIRE -144 -64 -144 -352
WIRE 0 -64 -144 -64
WIRE 384 -64 384 -160
WIRE 384 -64 256 -64
WIRE -144 -48 -144 -64
WIRE 384 -48 384 -64
WIRE 1200 -16 1200 -64
WIRE 0 0 0 -64
WIRE 64 0 64 -240
WIRE 128 0 128 -352
WIRE 192 0 192 -240
WIRE 256 0 256 -64
WIRE -144 48 -144 32
WIRE 384 48 384 32
WIRE 368 80 336 80
WIRE -336 96 -336 -160
WIRE 368 144 368 80
WIRE 368 144 336 144
WIRE -336 208 -336 176
WIRE -208 208 -336 208
WIRE 368 208 368 144
WIRE 368 208 336 208
WIRE 432 208 368 208
WIRE -336 224 -336 208
WIRE -80 224 -112 224
WIRE 368 224 368 208
WIRE -112 272 -112 224
WIRE 432 272 432 208
WIRE 432 272 336 272
WIRE -208 320 -208 208
WIRE -80 320 -208 320
WIRE -336 336 -336 304
WIRE 1584 400 336 400
WIRE -80 416 -224 416
WIRE 1584 448 1584 400
WIRE 1440 464 1440 -96
WIRE 1440 464 336 464
WIRE 1328 528 1328 -112
WIRE 1328 528 336 528
WIRE 1584 560 1584 528
WIRE 1520 592 1520 -96
WIRE 1520 592 336 592
WIRE -224 656 -224 416
WIRE 992 656 928 656
WIRE 48 688 48 672
WIRE 128 688 128 672
WIRE 208 688 208 672
WIRE 992 688 992 656
WIRE -224 768 -224 736
WIRE 48 784 48 752
WIRE 208 784 208 752
WIRE 928 784 928 656
WIRE 992 784 992 768
WIRE 992 784 928 784
WIRE 992 800 992 784
FLAG 128 688 0
FLAG -144 48 0
FLAG 1584 560 0
FLAG 384 48 0
FLAG 1088 -80 0
FLAG 1520 -208 OUT
FLAG 48 784 0
FLAG 368 224 0
FLAG -224 768 0
FLAG 1200 -16 0
FLAG 208 784 0
FLAG -112 272 0
FLAG -336 336 0
FLAG 992 800 0
SYMBOL LTC2952 128 304 R0
SYMATTR InstName U1
SYMBOL res 1424 -192 R0
SYMATTR InstName R3
SYMATTR Value 1K
SYMBOL res 1504 -192 R0
SYMATTR InstName R4
SYMATTR Value 100K
SYMBOL voltage -144 -64 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V1
SYMATTR Value PWL(0 4.2 20 2)
SYMBOL voltage -224 640 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
WINDOW 3 -19 229 Left 2
SYMATTR Value PWL(0 1 2 1 2.001 0 3 0 4.998 0 4.999 1 9 1 9.001 0)
SYMATTR InstName PB
SYMBOL voltage 384 -64 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V2
SYMATTR Value PWL(0 0 4 0 4.001 5 14 4 14.001 0)
SYMBOL cap 1072 -176 R0
SYMATTR InstName C4
SYMATTR Value 1µ
SYMATTR SpiceLine Rser=0.5
SYMBOL pmos -112 -304 R270
WINDOW 0 74 32 VRight 2
WINDOW 3 -11 74 VLeft 2
SYMATTR InstName Q1
SYMATTR Value FDS6875
SYMBOL pmos 368 -304 M270
WINDOW 0 72 54 VLeft 2
WINDOW 3 -14 68 VLeft 2
SYMATTR InstName Q2
SYMATTR Value FDS6875
SYMBOL pmos 96 -304 M270
WINDOW 0 74 32 VRight 2
WINDOW 3 -11 74 VLeft 2
SYMATTR InstName Q3
SYMATTR Value FDS6875
SYMBOL cap 32 688 R0
SYMATTR InstName C1
SYMATTR Value 100p
SYMBOL cap 192 688 R0
SYMATTR InstName C2
SYMATTR Value 100p
SYMBOL res -352 80 R0
SYMATTR InstName R1
SYMATTR Value 649k
SYMBOL res -352 208 R0
SYMATTR InstName R2
SYMATTR Value 100k
SYMBOL load 1184 -128 R0
WINDOW 3 48 36 Left 2
WINDOW 123 0 0 Left 2
WINDOW 39 48 64 Left 2
SYMATTR Value 2
SYMATTR SpiceLine load
SYMATTR InstName I1
SYMBOL res 1312 -208 R0
SYMATTR InstName R5
SYMATTR Value 1K
SYMBOL pmos 160 -304 R270
WINDOW 0 74 32 VRight 2
WINDOW 3 -11 74 VLeft 2
SYMATTR InstName Q4
SYMATTR Value FDS6875
SYMBOL res -16 -528 R0
SYMATTR InstName R6
SYMATTR Value 1m
SYMBOL res 240 -592 R0
SYMATTR InstName R7
SYMATTR Value 1m
SYMBOL voltage 992 672 R0
WINDOW 123 0 0 Left 2
WINDOW 39 24 44 Left 2
WINDOW 3 -19 229 Left 2
SYMATTR SpiceLine Rser=1k
SYMATTR Value PWL(0 1 2 1 2.001 0 3 0 3.001 1 5 1 5.001 0 6 0 6.001 1 8 1 8.001 0 9 0 9.001 1 16 1 16.001 0)
SYMATTR InstName PB1
SYMBOL voltage 1584 432 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
WINDOW 3 -19 229 Left 2
SYMATTR Value PWL(0 1 5 1 5.001 0 6 0 6.001 1)
SYMATTR InstName PB2
TEXT 496 704 Left 2 !.tran 20 startup

Reply

0 Karlson on Oct 25, 2021 6:43 PM in reply to Ashapiro

Ashapiro said:
Maybe take your circuit for a spin in LTspice to see if it works like you think it does.

Already done and I think everything works fine, but I tried to simulate 2952 some time ago in some exotic configuration and model did not behave as a real part did, that's why I ask my question.

Here is my current .asc:

Version 4
SHEET 1 3612 1076
WIRE 320 -576 256 -576
WIRE 64 -512 0 -512
WIRE 560 -464 128 -464
WIRE 0 -432 -16 -432
WIRE 320 -432 320 -576
WIRE 320 -432 272 -432
WIRE 64 -416 64 -512
WIRE 64 -416 0 -416
WIRE -112 -352 -144 -352
WIRE -16 -352 -16 -432
WIRE 0 -352 0 -416
WIRE 128 -352 128 -464
WIRE 128 -352 96 -352
WIRE 160 -352 128 -352
WIRE 256 -352 256 -496
WIRE 272 -352 272 -432
WIRE 384 -352 368 -352
WIRE -32 -240 -32 -304
WIRE 16 -240 16 -304
WIRE 16 -240 -32 -240
WIRE 64 -240 16 -240
WIRE 240 -240 240 -304
WIRE 240 -240 192 -240
WIRE 288 -240 288 -304
WIRE 288 -240 240 -240
WIRE 560 -208 560 -464
WIRE 1088 -208 560 -208
WIRE 1200 -208 1088 -208
WIRE 1328 -208 1200 -208
WIRE 1440 -208 1328 -208
WIRE 1520 -208 1440 -208
WIRE 1328 -192 1328 -208
WIRE 1088 -176 1088 -208
WIRE 1440 -176 1440 -208
WIRE 1520 -176 1520 -208
WIRE 384 -160 384 -352
WIRE 384 -160 -336 -160
WIRE 1200 -128 1200 -208
WIRE 1088 -80 1088 -112
WIRE -144 -64 -144 -352
WIRE 0 -64 -144 -64
WIRE 384 -64 384 -160
WIRE 384 -64 256 -64
WIRE -144 -48 -144 -64
WIRE 384 -48 384 -64
WIRE 1200 -16 1200 -64
WIRE 0 0 0 -64
WIRE 64 0 64 -240
WIRE 128 0 128 -352
WIRE 192 0 192 -240
WIRE 256 0 256 -64
WIRE -144 48 -144 32
WIRE 384 48 384 32
WIRE 368 80 336 80
WIRE -336 96 -336 -160
WIRE 368 144 368 80
WIRE 368 144 336 144
WIRE -336 208 -336 176
WIRE -208 208 -336 208
WIRE 368 208 368 144
WIRE 368 208 336 208
WIRE 432 208 368 208
WIRE -336 224 -336 208
WIRE -80 224 -112 224
WIRE 368 224 368 208
WIRE -112 272 -112 224
WIRE 432 272 432 208
WIRE 432 272 336 272
WIRE -208 320 -208 208
WIRE -80 320 -208 320
WIRE -336 336 -336 304
WIRE 1584 400 336 400
WIRE -80 416 -224 416
WIRE 1584 448 1584 400
WIRE 1440 464 1440 -96
WIRE 1440 464 336 464
WIRE 1328 528 1328 -112
WIRE 1328 528 336 528
WIRE 1584 560 1584 528
WIRE 1520 592 1520 -96
WIRE 1520 592 336 592
WIRE -224 656 -224 416
WIRE 992 656 928 656
WIRE 48 688 48 672
WIRE 128 688 128 672
WIRE 208 688 208 672
WIRE 992 688 992 656
WIRE -224 768 -224 736
WIRE 48 784 48 752
WIRE 208 784 208 752
WIRE 928 784 928 656
WIRE 992 784 992 768
WIRE 992 784 928 784
WIRE 992 800 992 784
FLAG 128 688 0
FLAG -144 48 0
FLAG 1584 560 0
FLAG 384 48 0
FLAG 1088 -80 0
FLAG 1520 -208 OUT
FLAG 48 784 0
FLAG 368 224 0
FLAG -224 768 0
FLAG 1200 -16 0
FLAG 208 784 0
FLAG -112 272 0
FLAG -336 336 0
FLAG 992 800 0
SYMBOL LTC2952 128 304 R0
SYMATTR InstName U1
SYMBOL res 1424 -192 R0
SYMATTR InstName R3
SYMATTR Value 1K
SYMBOL res 1504 -192 R0
SYMATTR InstName R4
SYMATTR Value 100K
SYMBOL voltage -144 -64 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V1
SYMATTR Value PWL(0 4.2 20 2)
SYMBOL voltage -224 640 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
WINDOW 3 -19 229 Left 2
SYMATTR Value PWL(0 1 2 1 2.001 0 3 0 4.998 0 4.999 1 9 1 9.001 0)
SYMATTR InstName PB
SYMBOL voltage 384 -64 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V2
SYMATTR Value PWL(0 0 4 0 4.001 5 14 4 14.001 0)
SYMBOL cap 1072 -176 R0
SYMATTR InstName C4
SYMATTR Value 1µ
SYMATTR SpiceLine Rser=0.5
SYMBOL pmos -112 -304 R270
WINDOW 0 74 32 VRight 2
WINDOW 3 -11 74 VLeft 2
SYMATTR InstName Q1
SYMATTR Value FDS6875
SYMBOL pmos 368 -304 M270
WINDOW 0 72 54 VLeft 2
WINDOW 3 -14 68 VLeft 2
SYMATTR InstName Q2
SYMATTR Value FDS6875
SYMBOL pmos 96 -304 M270
WINDOW 0 74 32 VRight 2
WINDOW 3 -11 74 VLeft 2
SYMATTR InstName Q3
SYMATTR Value FDS6875
SYMBOL cap 32 688 R0
SYMATTR InstName C1
SYMATTR Value 100p
SYMBOL cap 192 688 R0
SYMATTR InstName C2
SYMATTR Value 100p
SYMBOL res -352 80 R0
SYMATTR InstName R1
SYMATTR Value 649k
SYMBOL res -352 208 R0
SYMATTR InstName R2
SYMATTR Value 100k
SYMBOL load 1184 -128 R0
WINDOW 3 48 36 Left 2
WINDOW 123 0 0 Left 2
WINDOW 39 48 64 Left 2
SYMATTR Value 2
SYMATTR SpiceLine load
SYMATTR InstName I1
SYMBOL res 1312 -208 R0
SYMATTR InstName R5
SYMATTR Value 1K
SYMBOL pmos 160 -304 R270
WINDOW 0 74 32 VRight 2
WINDOW 3 -11 74 VLeft 2
SYMATTR InstName Q4
SYMATTR Value FDS6875
SYMBOL res -16 -528 R0
SYMATTR InstName R6
SYMATTR Value 1m
SYMBOL res 240 -592 R0
SYMATTR InstName R7
SYMATTR Value 1m
SYMBOL voltage 992 672 R0
WINDOW 123 0 0 Left 2
WINDOW 39 24 44 Left 2
WINDOW 3 -19 229 Left 2
SYMATTR SpiceLine Rser=1k
SYMATTR Value PWL(0 1 2 1 2.001 0 3 0 3.001 1 5 1 5.001 0 6 0 6.001 1 8 1 8.001 0 9 0 9.001 1 16 1 16.001 0)
SYMATTR InstName PB1
SYMBOL voltage 1584 432 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
WINDOW 3 -19 229 Left 2
SYMATTR Value PWL(0 1 5 1 5.001 0 6 0 6.001 1)
SYMATTR InstName PB2
TEXT 496 704 Left 2 !.tran 20 startup

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