Figuring Pinout of Voltage Regulator?

Op-Ivy · Jul 22, 2010

I just purchased a few low dropout voltage regulators and I can't figure out which way to turn the regulator to figure out the pinout.

There is a little indented dot on it. Does that have something to do with it?

Here is the regulator: TPS7150QP Texas Instruments Low Dropout (LDO) Regulators

Thanks!

lilimike · Jul 22, 2010

This very same link that you indicated, go there, click on the "Documents" tab and click on the "Datasheet" link, it's all there.

Mike

Reloadron · Jul 22, 2010

Yes, the indented dot is pin 1. Read the data sheet and note the pictures.

Ron

Op-Ivy · Jul 22, 2010

Reloadron said:
Yes, the indented dot is pin 1. Read the data sheet and note the pictures.

Ron

Thank you! I could see the pinout but I couldn't figure out which side was which. Is the dot always an indicator of pin 1?

Reloadron · Jul 22, 2010

Op-Ivy said:
Thank you! I could see the pinout but I couldn't figure out which side was which. Is the dot always an indicator of pin 1?

Yep. I can't think of a simple DIP chip I have seen that doesn't use the indent dot for pin one. Not to say there aren't any.

Ron

PatM · Jul 22, 2010

Op-Ivy said:
Thank you! I could see the pinout but I couldn't figure out which side was which. Is the dot always an indicator of pin 1?

Yes
Most Ic's have this indicator for pin 1

Op-Ivy · Jul 22, 2010

Alright so I wired it up and the output voltage is the same as the input. I think I may be wiring it wrong.

The pinout diagram is on the first page of the data sheet correct? There are more pinouts on other pages of the data sheet. What are those for? I'm not sure which to use.

Reloadron · Jul 22, 2010

Use the pinout for the exact version you have. You have an 8 pin DIP I believe?

Next:

SENSE-pin connection
The SENSE pin of fixed-output devices must be connected to the regulator output for proper functioning of the
regulator. Normally, this connection should be as short as possible; however, the connection can be made near
a critical circuit (remote sense) to improve performance at that point. Internally, SENSE connects to a
high-impedance wide-bandwidth amplifier through a resistor-divider network and noise pickup feeds through
to the regulator output. Routing the SENSE connection to minimize/avoid noise pickup is essential. Adding an
RC network between SENSE and OUT to filter noise is not recommended because it can cause the regulator
to oscillate.

Sense would be pin 7 on an 8 pin DIP package, You are connecting pin 7 correct? Also, I never used the chip but it has an Enable pin 2 which should be tied low to enable the chip.

Ron

Ron

Op-Ivy · Jul 22, 2010

Thanks Ron! I am not connecting pin 7 at the moment. Where did you find that little blurb? I would like to read more on this. (still learning the basics of electronics)

Reloadron · Jul 22, 2010

The data sheet is your best friend.

The Sense info is in there somewhere. Data sheets can sometimes be difficult to understand, especially when starting out and when the sheet addresses several versions of the part in several packages. You just muddle along and try to understand the terms.

Ron

Op-Ivy · Jul 22, 2010

Ah thank you. I found it now.

So now for my output I am getting .25v and it's a 5v fixed regulator. I am not sure why. I read some more in the data sheet and found that EN should be connected to ground. This is how it's all connected:

**broken link removed**

Am I connecting the right pins together?

Reloadron · Jul 22, 2010

Start reading around page 27 of the data sheet:

external capacitor requirements (continued)
As with most LDO regulators, the TPS71xx family requires an output capacitor for stability. A 10-μF
solid-tantalum capacitor connected from the regulator output to ground is sufficient to ensure stability over the
full load range (see Figure 43).

You need a cap hanging out there as mentioned. Also note R1 & R2 in the programming section. Like I mentioned, I never used this chip so I am winging it. Also, I will be offline soon so don't get discouraged if things still don't quite work.

Ron

Op-Ivy · Jul 22, 2010

Alright I will work on it. Thanks for all your help!

Op-Ivy · Jul 22, 2010

One last question. Why is there a different pinout on pg27?

Op-Ivy · Jul 22, 2010

Also I think the R1 and R2 are for the adjustable version?

Op-Ivy · Jul 30, 2010

I finally got it working. The capacitors were needed but the resistors aren't. Works like a charm now!

Reloadron · Jul 30, 2010

Glad it worked and yes, the resistors were for the adjustable versions. They did mention the caps in the data sheet.

Ron

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