Need help with LP2950CZ-3.0 Micropower Voltage Regulator from texas instruments

[muhibraza]

Hello Everyone !

I am trying to use the Texas Instruments LP2950CZ-3.0 as a voltage reference for A/D conversion with PIC18F26K22. But I have tested it outside the circuit, and it does not give 3.0V output. Instead it gives 4.55 V output on 5V input. I have two pieces and both show the same response on no-load. And the datasheet says it can give output current of 100mA but when I put a resistance of 470 Ohm as a load, then only milliVolts show up on output. Can anyone suggest what could be wrong ?

here's the schematic :
**broken link removed**

here's the first page of datasheet :
**broken link removed**

datasheer link :
https://www.ti.com/lit/ds/symlink/lp2950-n.pdf

Here's a picture of the regulator :


Here's a picture of my breadboard circuit :

 

[malli_1729]

attachment looks wrong.....give correct schematic....

 

[Audioguru]

You have the input and output pins connected backwards which might have destroyed the IC. The datasheet shows the pins from the bottom but you have the IC faced from the top.

 

[muhibraza]

ohh thanks for pointing that out Audioguru.
I'll check wih the correct connection tomorrow.

 

[muhibraza]

ok its working fine. Thanks Audioguru.

malli_1729
here's the schematic :


here's the first page of datasheet :


- - - Updated - - -

But it has rated minimum 3.0 V and right now there is 2.998 V appearing on output. One IC shows 2.998V and the other shows 2.985 V.

do you think it would be a suitable reference for A/D conversion with PIC ? I needed exact 3 Volt

 

[BigBoss]

ok its working fine. Thanks Audioguru.

malli_1729
here's the schematic :
View attachment 111765

here's the first page of datasheet :
View attachment 111766

- - - Updated - - -

But it has rated minimum 3.0 V and right now there is 2.998 V appearing on output. One IC shows 2.998V and the other shows 2.985 V.

do you think it would be a suitable reference for A/D conversion with PIC ? I needed exact 3 Volt

Is your Multimeter sufficiently accurate ???Handhelds typical %0.25-0.1 accuracy.Use a more accurate one and consider ambient temperature which is mentioned in the datasheet.
Also, these devices have tolerances and no device gives you 3.000 V exactly.They are not perfect..

 

[Easyrider83]

Use internal FVR module. It can produce 1.024V, 2.048V or 4.096V for ADC reference.

 

[Audioguru]

The datasheet says that when its junction is at 25 degrees C its output voltage is typically 3.0V but it could be anywhere from 2.97V to 3.03V so yours are fine.

 

[Easyrider83]

Anyway, 2950 is not a reference voltage source.

 

[muhibraza]

Anyway, 2950 is not a reference voltage source.

but see the first page of the datasheet, texas instruments have said that it can be used as a regulator or reference.
check : https://j.mp/1pECQzh

- - - Updated - - -

Use internal FVR module. It can produce 1.024V, 2.048V or 4.096V for ADC reference.

but I think the PIC I am using will not even generate 4.096 V. Am I right ? here's the datasheet :

 

[muhibraza]

ok I think thats a typing error in datasheet. it should be 4.096 V since the FVR chapter indicates this voltage instead of 2.096..