SN74LVC14A

Aaron Spaete

I am currently working on a design using the 74LVC14A.

There is a condition that may apply a voltage greater than the supply rails to the output of the device through a resistor.

The datasheet for the 74LVC14A shows an output clamp current of -50 ma when Vo<0.

There is no mention of conditions where the Vo may be greater than VCC.

Is there a method to protect the output stage for a fault condition that may pull the output greater than Vcc?

Some of our previous designs used the 74ACT14 which has a output clamp current of +/- 20 ma.

This current rating was used to determine the value of current limit resistor.

over 13 years ago

0 Chris Cockrill over 13 years ago

TI__Mastermind 46480 points

Since the LVC is overvoltage tolerant on the inputs it does not have a clamp diode to Vcc. You should not exceed 6.5V on the input. If you think the input will go over this then you should use an external diode to Vcc for clamping.

0 Tom Wittkop over 13 years ago in reply to Chris Cockrill

Prodigy 90 points

The condition that I am referencing is when a fault occurs to the load connected to the output of the 74LVC14A. The fault may result with an effective pull up resistor to 50 VDC. This will not be an issue if the output is low and the current is limited to less than 50 ma. My concern is when the output is high. Will the 74LVC14A continue to sink the load current or will the output go above VCC and damage the device?

0 Chris Cockrill over 13 years ago in reply to Tom Wittkop

TI__Mastermind 46480 points

The output also does not have a clamp diode to Vcc. It may be damaged if you go above Vcc +0.5V. You could use an external diode here also.

ACT14 and HCT14 would have internal clamp diodes if that is the way you want to go.

0 Tom Wittkop over 13 years ago in reply to Chris Cockrill

Prodigy 90 points

Is there anyway to predict if the damage will propagate farther than the output stage? Can it flow through device and cause damage other devices if the current is limited to less than 50 ma?

Is the 74AC14 available in the TSSOP package?

0 Aaron Spaete over 13 years ago in reply to Tom Wittkop

TI__Expert 4527 points

Tom,

It's available in a 14 pin TSSOP. Please see the following link:

http://www.ti.com/product/sn74ac14

SN74AC14PWR

ACTIVE

-40 to 85

0.20 | 1ku

TSSOP (PW) | 14

View

2000 | LARGE T&R

>5k

1k quantity lead time: In stock

SN74AC14PWRE4

ACTIVE

-40 to 85

0.20 | 1ku

TSSOP (PW) | 14

View

2000 | LARGE T&R

1K - 5K

1k quantity lead time: In stock

SN74AC14PWRG4

ACTIVE

-40 to 85

0.20 | 1ku

TSSOP (PW) | 14

View

2000 | LARGE T&R

1K - 5K

1k quantity lead time: In stock

0 Aaron Spaete over 13 years ago in reply to Tom Wittkop

TI__Expert 4527 points

Tom,

If you want the same temp range of -40C to 125C, then you can look at the Q1 version.

http://www.ti.com/product/sn74ac14-q1

Either way, they are the same pinout for the 14 pin TSSOP.

- Aaron

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SN74LVC14A