Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

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

Status
Not open for further replies.

muhibraza

Member level 1
Joined
Oct 11, 2010
Messages
38
Helped
3
Reputation
6
Reaction score
3
Trophy points
1,288
Activity points
1,578
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 :
View attachment 111738

here's the first page of datasheet :
View attachment 111739

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

Here's a picture of the regulator :
20141127_155019_Richtone(HDR).jpg

Here's a picture of my breadboard circuit :
20141127_154530_Richtone(HDR).jpg
 

Audioguru

Advanced Member level 5
Joined
Jan 19, 2008
Messages
9,283
Helped
2,141
Reputation
4,276
Reaction score
1,967
Trophy points
1,393
Location
Toronto area of Canada
Activity points
58,409
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.
 

Attachments

  • LP2951.png
    LP2951.png
    14.6 KB · Views: 17

muhibraza

Member level 1
Joined
Oct 11, 2010
Messages
38
Helped
3
Reputation
6
Reaction score
3
Trophy points
1,288
Activity points
1,578
ohh thanks for pointing that out Audioguru.
I'll check wih the correct connection tomorrow.
 

muhibraza

Member level 1
Joined
Oct 11, 2010
Messages
38
Helped
3
Reputation
6
Reaction score
3
Trophy points
1,288
Activity points
1,578
ok its working fine. Thanks Audioguru.

malli_1729
here's the schematic :
LP2960CZ-3.0.jpg

here's the first page of datasheet :
27-Nov-14 3.29.13 PM.png

- - - 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

Advanced Member level 5
Joined
Nov 17, 2001
Messages
5,112
Helped
1,529
Reputation
3,056
Reaction score
1,376
Trophy points
1,393
Location
Turkey
Activity points
30,743
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

Advanced Member level 5
Joined
Oct 11, 2011
Messages
1,608
Helped
374
Reputation
748
Reaction score
362
Trophy points
1,363
Location
Tallinn, Estonia
Activity points
8,577
Use internal FVR module. It can produce 1.024V, 2.048V or 4.096V for ADC reference.
 

Audioguru

Advanced Member level 5
Joined
Jan 19, 2008
Messages
9,283
Helped
2,141
Reputation
4,276
Reaction score
1,967
Trophy points
1,393
Location
Toronto area of Canada
Activity points
58,409
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.
 

muhibraza

Member level 1
Joined
Oct 11, 2010
Messages
38
Helped
3
Reputation
6
Reaction score
3
Trophy points
1,288
Activity points
1,578
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 :
01-Dec-14 10.45.52 AM.png
 

muhibraza

Member level 1
Joined
Oct 11, 2010
Messages
38
Helped
3
Reputation
6
Reaction score
3
Trophy points
1,288
Activity points
1,578
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..
01-Dec-14 12.52.10 PM.png
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top