LMC555: Maximum Operating Frequency in 50% duty Cycle

Nesh Johny

Part Number: LMC555

Hi,

Could you please confirm, what is the maximum frequency possible to be generated with following part numbers in 50% duty cycle (configuration attached) and -40°C to 125°C operating temperature.

Part Nos:

a) LMC555IM/NOPB

b) LMC555IMX/NOPB

Thanks and Regards,

Nesh

over 5 years ago

0 Ron Michallick over 5 years ago

TI__Guru**** 166216 points

Hello Nesh,

The short answer is 2 MHz if accuracy matters at all. 1 MHz if accuracy matters.

The higher frequency and lower Rc, the greater the variance from 50%. Is close to 50% good enough?

Supply voltage can be a factor; at 1.5V the max frequency will be lower.

0 Nesh Johny over 5 years ago in reply to Ron Michallick

Expert 1310 points

Hi Sir,

Supply Voltage will be around 12V and close to 50% duty is also fine.

Regards,

Nesh

0 Ron Michallick over 5 years ago in reply to Nesh Johny

TI__Guru**** 166216 points

Nesh,

Pin 3 is only about 20ns delayed from pin 7 so there is not much difference from using pin 7 or using pin 3.

The most accurate formula is also the most complex. Frequency is 1 / (TcH + TcL)

A more simple estimator to get in the ballpark, (further tuning changes may be needed)

Just replace (Ra + 2*Rb) with 2 * Rc

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LMC555: Maximum Operating Frequency in 50% duty Cycle