CD74HC4538-Q1 Output Pulse Width and SPICE Model

Jared Becker

Other Parts Discussed in Thread: CD74HC4538-Q1, SN74LV123A-Q1, SN74LV221A, SN74LV123A

Hi team,

I am reviewing the Output Pulse Width provided by CD74HC4538-Q1 for below configurations.
The datasheet contains the K factor and time constant for few combinations. Unfortunately it doesn't cover the design values I'm using.

VCC varies between 4.9V to 5.1V
Operating Temperature range -40°C to 125°C

Scenario -1: Rx=100k Cx=1uF

And

Scenario -2: Rx=150k Cx=10uF

Can you please provide the K value for my specific conditions?

Also, is it possible to obtain a SPICE model that can run on SIMetrix simulation tool?

Thank you,

Jared

over 7 years ago

0 Akeem Whitehead over 7 years ago

TI__Mastermind 27920 points

The appropriate Applications Engineer has been assigned to respond accordingly. Thank you for your patience.

0 ShreyasRao over 7 years ago

TI__Guru 57390 points

As per fig 3 , the K factor for 100Kohm is converging for higher capacitance and I would assume the K to be 0.68 for Rx=100k Cx=1uF .
you could also consider to use SN74Lv123a-q1 which is dual automotive qualified device.
I roughly calculate the tw = 0.68 *100K *1uF = 68ms . the R ,C can be adjusted for desired tw.

0 ShreyasRao over 7 years ago in reply to ShreyasRao

TI__Guru 57390 points

I do not see any model in the tools and software tab in the product folder, however , there are hspice and IBIS models available for sn74LV221A and sn74LV123A commercial versions.

0 Jared Becker over 7 years ago in reply to ShreyasRao

TI__Genius 11665 points

Hi Shreyas,

Ok, what about scenario #2?

-Jared

0 ShreyasRao over 7 years ago in reply to Jared Becker

TI__Guru 57390 points

hi Jared ,

I would estimate K to be 0.6 going by the trend since we do not have a graph to indicate the scenario.
What is pulse width desired , could you consider sn74LV221A and sn74LV123A with the models available ?

0 Jared Becker over 7 years ago in reply to ShreyasRao

TI__Genius 11665 points

Hi Shreyas,

Thank you for the reply. The situation is a bit more complex than just recommending a new part. Other than extrapolation from the curves already in the datasheet, is there any test/validation data to support the values you have pointed to?

thank you,
Jared

0 ShreyasRao over 7 years ago in reply to Jared Becker

TI__Guru 57390 points

Hi Jared ,

No, Unfortunately .

I do not have the char data to support the values. These are old parts acquired from Harris semiconductors and didn't have many collaterals moved over and the reason why trying to suggest other parts with the models available. The graphs are suggested values and other combinations must be deduced from them. The char wouldn't have k values for every different combinations of R C values either.

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CD74HC4538-Q1 Output Pulse Width and SPICE Model