LM4128: Minimum VIN

Shuji Ishiwata

Mastermind 8880 points

Part Number: LM4128

Hi All,

I have a question about LM4128.

Maximum VIN is listed.

However, the minimum value is not specified. What is the minimum VIN value?

Also, what is the EN condition for VIH min =65%?

For example @EN=3.3V etc..,

Best Regards,
Ishiwata

over 3 years ago

0 Trailokya Rai over 3 years ago

TI__Genius 11401 points

Hi Ishiwata

Point 6 in footnote of the electrical table explains the min VIN requirement. Min Vin should be >= Vout + Drop out voltage .

Condition ofr EN has been tested at VIN = 5V . This meand min VIH = 0.65*5V = 3.3V . VIH will depend on VIN . It will reduce with VIN voltage.

Regards

Trailokya

0 Shuji Ishiwata over 3 years ago in reply to Trailokya Rai

Mastermind 8880 points

Hi Trailokya

Thank you for your reply and sorry for the late reply.

About the VI minimum, I understand.

What is the VIN threshold voltage at which VOUT is output?

And tell me the UVLO value of VIN.

Best Regards,
Ishiwata

0 Trailokya Rai over 3 years ago in reply to Shuji Ishiwata

TI__Genius 11401 points

Ishiwata San

Vout will be output with the dropout condition highlighted below

UVLO is not defined for REF part. You should keep the VIN above VREF + dropout voltage to ensure proper regulation.

Regards

Trailokya

0 Shuji Ishiwata over 3 years ago in reply to Trailokya Rai

Mastermind 8880 points

Hi Trailokya-san,

Thank you for your kind response.

I still don't understand.

The dropout voltage is 400mV.
For example, if you input 5V and output 3.3V, VREF will be output when the input is 3.7V.
Do you agree with this understanding?

Best Regards,
Ishiwata

0 Trailokya Rai over 3 years ago in reply to Shuji Ishiwata

TI__Genius 11401 points

Ishiwata

Vref will be 3.3V (regulated voltage) when VIN >= 3.7V . VREF will not be stable below 3.7V Vin.

Regards

Trailokya

0 Shuji Ishiwata over 3 years ago in reply to Trailokya Rai

Mastermind 8880 points

Hi Trailokya

Thank you for your reply.

This will be the resulting waveform at the customer.

VREF starts to output when VIN rises to 1.6V.
Please explain why VREF is output when VIN = 1.6V.

I will always appreciate your kind support.

Best Regards,
Ishiwata

0 Trailokya Rai over 3 years ago in reply to Shuji Ishiwata

TI__Genius 11401 points

Ishiwata San

This internal circuits will trigger and circuit will start giving output. Vref will follow Vin untill Vin crosses VREF+ drop out, in other words line regulation spec will not hold good untill VIN crosses VREF+ DO.

UVLO is not guranteed spec in the data sheet as this is analog IC , hence we define minimum VIN where REF pin will have regulated output.

Regards

Trailokya

0 Shuji Ishiwata over 3 years ago in reply to Trailokya Rai

Mastermind 8880 points

Hi Trailokya-san,

Thank you for your kind response.

There is ” This internal circuits will trigger ” by your comment.
Is that trigger voltage 1.6V?

I understand that VREF starts output by triggering the internal circuitry.

I will always appreciate your kind support.

Best Regards,
Ishiwata

0 Trailokya Rai over 3 years ago in reply to Shuji Ishiwata

TI__Genius 11401 points

Hi Ishiwata san

Refernce is designed to meet the drop out spec not the UVLO as this is not data sheet guranteed parameter. Hence variation may be large. It is not guranteed. Can you please tell why customer care for UVLO?

Regards

Trailokya

0 Shuji Ishiwata over 3 years ago in reply to Trailokya Rai

Mastermind 8880 points

Hi Trailokya-san,

Thank you for your reply.

Customers don't care about UVLO.
A customer wants to control the VREF output of the LM4128.
For that reason, we are checking which voltage of VIN triggers the output of VREF.
So customer is measuring the waveform at startup.

Best Regards,
Ishiwata

0 Trailokya Rai over 3 years ago in reply to Shuji Ishiwata

TI__Genius 11401 points

Ishiwata San

Can you please explain what do you mean by "customer wants to control the VREF output of the LM4128"

Regards

Trailokya

0 Shuji Ishiwata over 3 years ago in reply to Trailokya Rai

Mastermind 8880 points

Hi Trailokya-san,

Thank you for your reply.

Customers care about the timing of input to subsequent devices.
Therefore, the customer wants to estimate the min/max of the time that VREF is output.

So I'm asking about the VIN to VREF relationship.

Best Regards,
Ishiwata

0 Trailokya Rai over 3 years ago in reply to Shuji Ishiwata

TI__Genius 11401 points

Hi Ishiwata San

Customer can control VREF output with EN pin. Make sure the supply is up and then enable should come. VREF will not come up until enable goes high.

Hope this information helps your customer.

Regards

Trailokya

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LM4128: Minimum VIN