LM4121: LM4121IM5-ADJ/NOPB

C KUMAR

Part Number: LM4121

Hello Sir/Madam,

I am using LM4121IM5-ADJ/NOPB in our design for 1.65 Voltage Reference.

I selected the resistors R1 = 36 K ohms and R2 = 100K for the VOUT = [Vref(1+ R1/R2] − Ibias• R1. Vref =1.216 and Ibias = 40 nA

My expected VOUT is 1.65 Volts but I am getting 1.60 V

Could you suggest how to resolve it?

Thanks and Regards,

Sarath Kumar C

over 6 years ago

0 Marcoo Z over 6 years ago

TI__Mastermind 19580 points

Hi Kumar,

Can you show me a schematic?
What are the actual resistances of your resistors?
What is the Vref Voltage at the pin when you are testing this?

-Marcoo

0 C KUMAR over 6 years ago in reply to Marcoo Z

Prodigy 30 points

Hi Marcoo,

Thanks for your reply. Please find the below schematics I used.

The values of the resistances R1 and R2 when measured in circuit is 31.25 K and 62.9 K and the VRef voltage is 1.199 V when measured at ADJ pin.

In addition to this I tested using R1 = 3.6K and R2 = 10K, I got VRef is 1.217 V but VOUT is 1.44 V

Thanks and Regards,

C SARATH KUMAR

0 Marcoo Z over 6 years ago in reply to C KUMAR

TI__Mastermind 19580 points

Hi Sarath,

Can you try another LM4121 and see if it the issue persists?
What is the ESR of C1? or what type of capacitor is it?

-Marcoo

0 C KUMAR over 6 years ago in reply to Marcoo Z

Prodigy 30 points

Hi Marcoo,

Thanks for your reply.

I tried with another LM4121. The issue is same as before. The part that I used for C1 is C1608C0G1H470J080AA which is low ESR

Thanks & Regards,

C SARATH KUMAR.

0 Marcoo Z over 6 years ago in reply to C KUMAR

TI__Mastermind 19580 points

Hi Sarath,

It seems that the problem can be the capacitor ESR. Can you try a smaller capacitor like 0.022uF? or add a 0.5 Ohm resistor in series to increase the ESR?

-Marcoo

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LM4121: LM4121IM5-ADJ/NOPB