LMC555: What is the recommendation to suppress the unexpected output just after the startup?

Yoshikazu Kawasaki

Part Number: LMC555
Other Parts Discussed in Thread: TINA-TI, TLC3555-Q1

Tool/software:

Hello,

My customer has unexpected output pulse issue just after startup like this thread shows. Since the output of LMC555 controls the motor driver in their system, the motor moves unexpectedly, so they'd like to suppress the output of LMC555. I looked through the threads, but I'm not sure what the best way to suppress the output just after startup. Would you please tell me the recommendation?

https://e2e.ti.com/support/clock-timing-group/clock-and-timing/f/clock-timing-forum/1125240/lmc555-how-to-handle-the-reset-pin/4193990?tisearch=e2e-sitesearch&keymatch=LMC555#4193990

It seems my customer uses simulator TINA-TI and if the power supply is later than \TRIGGER and THRESHOLD pins, they don't see the unexpected output. Therefore they think they should follow the sequence shown below, but do you think you can guarantee that?

1. Signal on \TRIGGER and THRESHOLD

2. Power on V+

3. RESET release

Best Regards,

Yoshikazu Kawasaki

3 months ago

0 Chris Featherstone 3 months ago

TI__Mastermind 23040 points

Hi Yoshikazu,

Unfortunately there is no other method except for the one in the link below.

https://www.ti.com/document-viewer/lit/html/SSZTAD3

The timer chips do not have power on reset circuitry and the output will always be unpredictable during the startup process. The reset pin is not meant to be used as a power on reset function. Once the chip is fully powered on the reset pin will work as expected but not during power on. The simulation may show that the unexpected output is not present however there is no way to assure this since there is not any power on reset circuitry in the device.

Best Regards,

Chris Featherstone

0 Chris Featherstone 3 months ago

TI__Mastermind 23040 points

Hello Yoshikazu,

Our newly released and much improved timer the TLC3555-Q1 has power on reset. This may be an option for replacement of the timer instead of building a circuit around the old timer. I will have an EVM released very soon for this device as well.

https://www.ti.com/product/TLC3555-Q1

https://www.ti.com/lit/ug/slou565/slou565.pdf?ts=1724085293338&ref_url=https%253A%252F%252Fwww.google.com%252F

Best Regards,

Chris Featherstone

0 Yoshikazu Kawasaki 3 months ago in reply to Chris Featherstone

Intellectual 741 points

Hello Chris-san,

Thank you very much for your quick reply.

> Unfortunately there is no other method except for the one in the link below.

I looked at the link you showed, but the output of LMC555 just startup should be high enough which makes the JFET off because the motor driver can move by the output of the LMC555, so Vout shown below will go up enough to drive the motor driver on their system even it has P-type JFET. Therefore the method wouldn't work. Am I correct?

The JFET can be N-type, but it is the same as shown above, the output of the LMC555 will be higher than Vth of N-type, so the N-type JFET will be on which makes Vout high level.

Best Regards,

Yoshikazu Kawasaki

0 Yoshikazu Kawasaki 3 months ago in reply to Chris Featherstone

Intellectual 741 points

Hello Chris-san,

Thank you for proposing the new timer. It is drop-in replacement if my customer uses SOIC(8)?

Best Regards,

Yoshikazu Kawasaki

+1 Chris Featherstone 3 months ago in reply to Yoshikazu Kawasaki

TI__Mastermind 23040 points

Hello Yoshikazu-san,

Yes the timer devices all have the same pinout including the new device. Here is the pinout of the new TLC3555-Q1 SOIC (8). The evaluation module will be released soon as well to evaluate the timer.

Here is a link to the product datasheet for the new timer.

https://www.ti.com/product/TLC3555-Q1?bm-verify=AAQAAAAJ_____2cVCv_UjOVgfa0I4pbHa6t0ohBQQ01aqizFXeH-poQnLNceZrACjb83bx7XNFO8wAb9da2LGYrhWxkf424_BTl7u3m_O7pc1wJSSChu4G4oOeafs8mA7OvmV0L60jjOUrH18vYRP99N8pTA8AnW8xaNbYcBjzLK7E4qneX4OXyOh1OBa18-7a6QHzaXsHaYoeAWlHBRQ84iYPLm7rkQfe3F1g0b1NaCEH2o8lkuttbiEcGboEc-tTM44Z8KX1_a4XdHOR1FY2ZGxvT8NMsWF5l3ieGLjjhxHam4pLwgGbyM

Best Regards,

Chris Featherstone

0 Yoshikazu Kawasaki 3 months ago in reply to Chris Featherstone

Intellectual 741 points

Hello Chris-san,

Thank you for your comments. I'll recommend TLC3555-Q1 then. I hope you can add the information of TLC3555-Q1 in LMC555 web page as an alternative. The current LMC555 web page only shows the information of LMC555.

Best Regards,

Yoshikazu Kawasaki

0 Chris Featherstone 3 months ago in reply to Yoshikazu Kawasaki

TI__Mastermind 23040 points

Hi Yoshikazu-san,

I will let our systems and marketing team know. Thank you for the feedback.

Best Regards,

Chris Featherstone

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LMC555: What is the recommendation to suppress the unexpected output just after the startup?