LM334: Accuracy of LM334M/NOPB

RAMAKRISHNA NAGARAJU GUDLA

Prodigy 120 points

Part Number: LM334

Hello Team,

Greetings !!!

Please refer the attachment. We are using LM334M/NOPB as a constant current source.

We observed that the current is drifting from initial power on value.

The measurements with Fluke 87 multimeter shows that the initial current (Iset) is 123.8uA. Eventually the current is increasing to approximately 128.2uA.

It sounds like the IC is temperature sensitive and hence the Iset value is changing.

In this regards, I would like to know

1) Is it observed value change in current still in accuracy range of LM334M/NOPB ?

2) What is the total accuracy can be expected from LM334M/NOPB with the basic current source design that we have ?

3) How do we improve our design to have tighter tolerance ?

4) Is there any evaluation board available ?

Thanks in advance for your help. Please feel free to ask if I miss any information

Thanks and Regards

G R K Nagaraju

over 2 years ago

0 Ben C over 2 years ago

TI__Mastermind 37695 points

Hi GRK,

Please see my response below in red:

1) Is it observed value change in current still in accuracy range of LM334M/NOPB ?

Yes, please see figure below. As temperature increases, the voltage across the Rset resistor changes in a positive trend.

2) What is the total accuracy can be expected from LM334M/NOPB with the basic current source design that we have ?

The part to part variation of the current accuracy is 12% (max) and it will change over temperature because the VR voltage (see above) is changing over temperature. Please see below:

3) How do we improve our design to have tighter tolerance ?

You can improve your design by following what is mentioned on page 8 of the datasheet.

4) Is there any evaluation board available ?

Unfortunately, there is no evaluation board for this device.

Ben

0 RAMAKRISHNA NAGARAJU GUDLA over 2 years ago in reply to Ben C

Prodigy 120 points

Thanks for the response Ben.

As I mentioned , up on power on the current shows 123.8uA and eventually the current reaches and stable at 128.2uA. The change is 4.4uA. The resistor value is 549 Ohm. So the delta change in voltage would be 2.4156mV change in voltage across RSET. The temperature should raise from initial value by 11.323125 Deg. C to cause 2.4156mV change in voltage across RSET. The power consumption of IC is around 0.625mW (5V x 125uA). I could not understand 0.625mW of power dissipation would raise the temperature of IC by 11.33 Deg. C.

Is there any other reason that could make the increase in set current from power on value ?

Thanks