TL431A-Q1 Delaly timer

Hello Asaka-san,

Please try to repost your schematic.

1. Please refer to Section 10.2.2 in the TL431 datasheet for calculating the Vk voltage.

2. The absolute maximum between Vk and Vref is 34.5 V, the recommended maximum is 33.5 V. The Vka max is given, which is the difference between Vka and ground. Vref is always 2.5V relative to gnd, so the difference gives you Vka to Vref max.

May I also suggest that you look at the ATL431 as a replacement for the TL431. It is also a 2.5 V reference, but can be biased with much less current (35 uA as opposed to 1 mA).

Best,
Michael

Hello Michael san,

Thank you for the reply.Please see the attached picture.
This is the same schematic with Figure 27 on TL431A-Q1 datasheet.
And I attached TINA-TI simulation result. I can't understand the calculation of Charode voltage of this simulation.

Best Regards,
Ryuji Asaka

Ryuji san

The simulation does not give correct results. The delay time is probably close but the voltages are incorrect.
VOUT will drop a little before VF2 get to 2.5V; this is why R2 is there to use any early current. (ICC) up to 1mA per data sheet.
For ATL431 this current is about 40uA instead.

After delay, VOUT goes to about 2V and VF2 won't go over 2.7V

Hello Ron san,

Thank you for your help.
Could you please let me know the reason of the "about 2V" after delay?
Is this 2V internal diode Vf ?

Concerning ATL431, the customer request Q100 device and the customer interested the price,,, we propose TL431A-Q1.

Best Regards,
Ryuji Asaka

Ryuji san,

The 2V is the headroom required to keep the output transistor on.
The reference voltage can't be more than cathode + Vf (~0.7V); it will forward bias from reference to cathode internally.

Hello Ron san,

Thank you for the reply.
The cusotmer would like to use this application as SW.
Thus they expect that the VK voltage will be 0V.

(1)Vk min
Could you please let me know the minnimum value of Vk in this application ?
The customer measured the voltage as 1.8V.

(2) Other application
Are the any other reference circuit of TL431A-Q1 for their expected operation?
Their expected operation is the following.
-The battery is connected to TL431A-Q1 circuit.
-LED is turned on aafter delay.
-VK of TL431A-Q1 is 0V.

Best Regards,
Ryuji Asaka

Ryuji san,

TL431A-Q1 is one of the shunts I need to characterize for my shunt comparator application note.
I can get projected VKA range this week.

There is no need for VKA to be 0V. With 12V supply there is plenty of voltage to spare.

Hello Ron san,

Thank you for your support.
I'm looking forward to your reply.

Best Regards,
Ryuji Asaka

Ryuji san,

I didn't get time to take the data. Cathode voltage will easily be within 1.8V to 2.2V range for all samples and all temperatures.
There isn't much movement.

Hello Ron san,

Thank you for the checking.
Could you please let me know the samples qty? And please let me know the tested IKA current.

Best Regards,
Ryuji Asaka

Hello Ryuji-san,

Ron provided a range that the voltage will always fall within, but was not able to test samples to get what would be a typical value.

The range of 1.8V to 2.2V will apply for all samples across acceptable Ika values.

Best,
Michael

Hello Michael san,

Sory for my misunderstanding.
I understood.

The customer would like to set the Vout to 0V after delay.
Are there any idea of schematics?

Best Regards,
Ryuji Asaka

Ryuji-san,

Once the VK voltage is at a minimum, I can't think of a way to pull to ground off hand.
I am sure that there is a way to do it.
Ultimately, what are you trying to achieve?
You are trying to pull the output to ground after a specified delay time?

Best,
Michael

Hello Michael san,

Sorry for my late reply.

We would like to pull the output to grohnd after specified delay time for turn off the NPN transistor.
If we add a PNP transister we can acieve but BOM was increased.

Best Regards,
Ryuji Asaka