Author Topic: Datasheet interpretation for 74HC590 rise and fall times  (Read 743 times)

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Offline GreyAreaTopic starter

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Datasheet interpretation for 74HC590 rise and fall times
« on: August 30, 2019, 08:37:34 am »
Hi, I'm reading the datasheet for the TI SN74HC690A counter.  (https://www.ti.com/lit/gpn/sn74hc590a)

Under the recommended operating conditions I can see that at Vin of 4.5 the max Input transition (rise and fall) time is 500ns.  So this might be a silly question but the signal I'm trying to count has quite a slow Tr and Tf of about 600ns.  Can I assume that I'm out of spec for a reliable count with this part and that I need to clean this up by adding schmitt trigger?  If so, can anyone recommend a suitable jellybean schmitt trigger?
 

Offline StillTrying

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Re: Datasheet interpretation for 74HC590 rise and fall times
« Reply #1 on: August 30, 2019, 11:44:27 pm »
"the signal I'm trying to count has quite a slow Tr and Tf of about 600ns."

Are they the 10% to 90% times. From the note underneath it looks to me that if you have fast 0.5V to 1.5V times and a good gnd you'd just about get away with your 600ns, it's a bit of a grey area. :)

If this device is used in the threshold region (from VILmax = 0.5 V to VIHmin = 1.5 V), there is a potential to go into the wrong state from induced grounding, causing double clocking. Operating with the inputs at tt = 1000 ns and VCC = 2 V does not damage the device; however, functionally, the CCLK and RCLK inputs are not ensured while in the shift, count, or toggle operating modes.

74HC14 or 74HC132 if nand is useful.
.  That took much longer than I thought it would.
 


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