FF with High True Enables

The only FF devices I can find with a high true reset control are the CD401

3 and CD4027 and the part number variations of those parts. Is this it? D o none of the AC, AHC, HC, VLC,... use high true resets?

I thought there were parts made in the HC or AHC technology with the 40xx n umbers and functions, but I'm not finding them at digikey.

The circuit I'm using it in is a hybrid analog/digital thing. I want to de tect a voltage (representing a motor current) has risen above a threshold f or some amount of time, then set a FF that controls power to a motor, disab ling the motor.

I went through an iteration of this circuit using MOSFETs (1 N-channel and

1 higher power P-channel) to form the FF and two more to provide control fr om lower voltage inputs. The input that turns the motor off is from a comp arator that detects transitions above the threshold. The output is OC with a pullup and a cap to act as a timer. Reaching the threshold of the input control FET flips the flop turning off the motor. The other input is from the MCU to turn it back on. Another FETs is used to detect the state of t he FF to match the MCU input voltage.

Using a proper FF allows three of the transistors to be removed and a few p assives. The level of the RC output from the comparator is used to control the reset input to the FF. The MCU input is direct to the clock input whi ch with the D held high sets the FF. The FF output then drives the FETs th at control the motor. Simple. But...

I'm concerned that this is using the input threshold to set the level of th e RC on the output of the comparator. It looks like it can cause a range o f 50 to 200 ms to detect the high current condition. I was hoping to find a different flavor of device with a better specified input spec, but this r equires a high true rest and there only seems to be two PNs that have this, CD4013 and CD4027.

I'm pretty sure the variation in timing is not at all important. This is t o detect the motor running to the stops if the software craps out. Turning off in 50 ms won't be so different from 200 ms I expect. It's not like we have any hard spec. This project is running pretty open loop in that rega rd.

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  Rick C. 

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Ricketty C
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I pushed the transistor version around until I found a couple more optimiza tions and I think that is the better circuit now. No new parts added to th e BoM other than the P-MOSFET needed to handle the motor current.

I optimized it by not using the PFET as part of the FF since that made the FF all 15 volt logic which was hard to interface to the low voltage circuit . I could use two NFETs to make the FF on the low voltage rail, but the fi nal optimization was to eliminate the NFET interfacing the timing RC by put ting the OC comparator output in series with one of the NFETs. That create d an OR gate to allow the transistor to accept two inputs.

I added two resistors in the load of the other NFET so there was a node the MCU can pull up or down through a cap to turn the motor back on or to turn it off although that should not be needed as there is a motor controller t o handle that. This circuit is kill the motor power if it goes to the stop s too long.

I'm pretty happy with the result and no logic chip required.

Here is the LTspice circuit if anyone cares to see it.

Version 4 SHEET 1 1752 708 WIRE -688 -256 -704 -256 WIRE -704 -240 -704 -256 WIRE 416 -192 400 -192 WIRE 416 -176 416 -192 WIRE 656 -112 640 -112 WIRE -688 -96 -704 -96 WIRE -496 -96 -512 -96 WIRE 656 -96 656 -112 WIRE -704 -80 -704 -96 WIRE -496 -80 -496 -96 WIRE 256 -64 240 -64 WIRE 304 -64 256 -64 WIRE 416 -64 416 -96 WIRE 416 -64 368 -64 WIRE 480 -64 416 -64 WIRE 560 -64 480 -64 WIRE 832 -48 816 -48 WIRE 416 -32 416 -64 WIRE -288 0 -320 0 WIRE -48 0 -288 0 WIRE 832 0 832 -48 WIRE 656 16 656 -16 WIRE 656 16 512 16 WIRE 736 16 656 16 WIRE 784 16 736 16 WIRE -320 32 -320 0 WIRE -496 48 -496 0 WIRE -432 48 -496 48 WIRE -368 48 -432 48 WIRE 656 48 656 16 WIRE -688 64 -704 64 WIRE -704 80 -704 64 WIRE 352 80 320 80 WIRE 416 80 416 48 WIRE 416 80 352 80 WIRE -496 96 -496 48 WIRE -368 96 -400 96 WIRE -400 112 -400 96 WIRE 416 112 416 80 WIRE -320 128 -320 112 WIRE 560 128 560 -64 WIRE 608 128 560 128 WIRE 832 144 832 96 WIRE 912 144 832 144 WIRE 960 144 912 144 WIRE -144 176 -160 176 WIRE 832 176 832 144 WIRE 960 176 960 144 WIRE -496 192 -496 176 WIRE -496 192 -512 192 WIRE -144 192 -144 176 WIRE 512 192 512 16 WIRE 512 192 464 192 WIRE -688 224 -704 224 WIRE 416 224 416 208 WIRE -704 240 -704 224 WIRE 96 256 80 256 WIRE 768 272 752 272 WIRE 832 272 832 256 WIRE 832 272 768 272 WIRE 96 288 96 256 WIRE 832 288 832 272 WIRE 960 288 960 256 WIRE -144 304 -144 272 WIRE 16 304 -144 304 WIRE 64 304 16 304 WIRE 208 320 128 320 WIRE 272 320 208 320 WIRE 400 320 352 320 WIRE 464 320 400 320 WIRE 656 320 656 144 WIRE 656 320 464 320 WIRE -144 336 -144 304 WIRE -48 336 -48 0 WIRE 16 336 -48 336 WIRE 64 336 16 336 WIRE 400 352 400 320 WIRE -560 368 -576 368 WIRE -48 368 -48 336 WIRE 96 368 96 352 WIRE -576 384 -576 368 WIRE 832 384 832 352 WIRE -688 432 -704 432 WIRE -144 432 -144 416 WIRE 400 432 400 416 WIRE -704 448 -704 432 WIRE -48 480 -48 448 FLAG 96 368 0 FLAG -48 480 0 FLAG -704 432 SIG FLAG -704 224 NOISE FLAG -704 528 0 FLAG -704 320 0 FLAG -496 -96 SIG FLAG -496 192 NOISE FLAG -288 0 Input FLAG 16 336 U1+ FLAG 208 320 SIXAMPS FLAG -320 128 0 FLAG -400 112 0 FLAG -144 432 0 FLAG 16 304 VREF FLAG -144 176 3V3 FLAG 400 432 0 FLAG -432 48 SUM FLAG -704 160 0 FLAG -704 64 3V3 FLAG -704 0 0 FLAG -704 -96 5V FLAG 656 -112 VIN FLAG 736 16 OFF FLAG 832 -48 VIN FLAG -576 464 0 FLAG -576 368 VIN FLAG 352 80 ON FLAG 416 224 0 FLAG 96 256 3V3 FLAG -704 -160 0 FLAG -704 -256 MOT_ON FLAG 416 -192 3V3 FLAG 256 -64 MOT_ON FLAG 464 320 OVR FLAG 480 -64 FORCE FLAG 960 288 0 FLAG 912 144 VMOT FLAG 832 384 0 FLAG 768 272 DIODE SYMBOL voltage -704 64 R0 WINDOW 123 0 0 Left 0 WINDOW 39 24 124 Left 2 SYMATTR SpiceLine Rser=0.01 SYMATTR InstName V1 SYMATTR Value 3.3 SYMBOL res -64 352 R0 SYMATTR InstName R3 SYMATTR Value 1.5K SYMBOL voltage -704 432 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 WINDOW 3 24 96 Left 1 SYMATTR Value PWL(0 0 0.5 0 0.51 4 1 4 1.005 8 1.05 8 1.055 4 1.1 4 1.105 8 1.15 8 1.155 4 1.2 4 1.205 8 1.25 8 1.255 4 1.3 4 1.305 8 1.35 8 1.355 4 1 .4 4 1.405 8 1.45 8 1.455 4 1.5 4 1.505 8 1.55 8 1.555 4 1.6 4 1.605 8 2 8

2.005 4 2.6 4 2.605 8) SYMATTR InstName V2 SYMBOL bv -704 224 R0 SYMATTR InstName B1 SYMATTR Value V=0.2*(white(2e1*time)) SYMBOL res -512 -96 R0 SYMATTR InstName R10 SYMATTR Value 1k SYMBOL res -512 80 R0 SYMATTR InstName R11 SYMATTR Value 100k SYMBOL res -160 176 R0 SYMATTR InstName R1 SYMATTR Value 1Meg SYMBOL g -320 16 R0 WINDOW 3 16 98 Left 2 SYMATTR Value 142.25E-6 SYMATTR InstName G1 SYMBOL cap 384 352 R0 SYMATTR InstName C1

SYMBOL Comparators\\LTC1841 96 320 R0 WINDOW 3 25 58 Left 2 SYMATTR InstName U1 SYMBOL res 368 304 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R4 SYMATTR Value 1k SYMBOL res -160 320 R0 SYMATTR InstName R2 SYMATTR Value 620k SYMBOL voltage -704 -96 R0 WINDOW 123 0 0 Left 0 WINDOW 39 24 124 Left 2 SYMATTR SpiceLine Rser=0.01 SYMATTR InstName V3 SYMATTR Value 5 SYMBOL res 640 -112 R0 SYMATTR InstName R8 SYMATTR Value 46k4 SYMBOL pmos 784 96 M180 SYMATTR InstName M3 SYMATTR Value AOD4185 SYMBOL voltage -576 368 R0 WINDOW 123 0 0 Left 0 WINDOW 39 24 124 Left 2 SYMATTR SpiceLine Rser=0.01 SYMATTR InstName V4 SYMATTR Value PULSE(0 14.7 0.01 0.02 0.12 15) SYMBOL nmos 464 112 M0 SYMATTR InstName M1 SYMATTR Value 2N7002 SYMBOL voltage -704 -256 R0 WINDOW 123 0 0 Left 0 WINDOW 39 24 124 Left 2 SYMATTR SpiceLine Rser=0.01 SYMATTR InstName V5 SYMATTR Value PULSE(3.3 00 0.1 10us 10us 0.01 2.4) SYMBOL res 400 -192 R0 SYMATTR InstName R7 SYMATTR Value 212k SYMBOL nmos 608 48 R0 SYMATTR InstName M2 SYMATTR Value 2N7002 SYMBOL res 400 -48 R0 SYMATTR InstName R6 SYMATTR Value 46k4 SYMBOL cap 368 -80 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C2 SYMATTR Value 100nF SYMBOL ind 944 160 R0 SYMATTR InstName L1 SYMATTR Value 60mH SYMATTR SpiceLine Ipk=20 Rser=2 SYMBOL schottky 848 352 R180 WINDOW 0 2 60 Right 2 WINDOW 3 4 1 Right 2 SYMATTR InstName D1 SYMATTR Value RBR30T60A SYMATTR Description Diode SYMATTR Type diode SYMBOL res 816 160 R0 SYMATTR InstName R5 SYMATTR Value 0R1 TEXT 16 176 Left 3 !.tran 0 3 0 0.001 TEXT 1032 -184 Right 3 ;Alternate Part - DMP3007SCG TEXT 176 -144 Right 3 ;From MCU TEXT -392 -88 Left 3 ;Motor Controller\nCurrent Sense Output TEXT 32 416 Left 2 ;Alternate Parts -\nLMC6772 in SOIC8 or VSSOP8\nTLV1702 in VSSOP8 \nTLV1704 in TSSOP14 (quad)

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Ricketty C

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