OpAmp and reference recomendations

- H
- Hammy
  
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posted
15 years ago

Sun, May 4, 2008 9:28 PM

I got tired of looking for a FET LDO that meets my line and load specs, so I'm building my own. The LP38691 is the closest I could find thats in stock and doesnt cost a lot,and with that I would be operating above the max recomended operating voltage. Just below the absoulute maximum ratings. Yes I'm already using a diode to drop excess voltage.

The LP38691

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So if anyone with experience in LDO's could recommend:

1.A good single supply rail to rail opamp, low power consumption.

2.A low power reference.

I've already built an LM324 based LDO here

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I'm using an NTR0202PL as the pass element (400mA P-Chan Fet) SOT-23 so I cant test it at full load until I get some beefier Fets.

Vin 6.3V to 11.5V.

I out 5mA- 100mA

Vout 5.7V

For the one I built I'm using an LT1009 as a reference this alone requires >1mA of bias. What I'm trying to do is get power consumption as low as possible when in standby. With my lm324 it's at 3.2mA, about

2.2 mA of that is for the unused opamp's in the LM324 and the reference. If I can't get it below 300uA I'll just use the LP2975.

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Does anyone know of anything similar to the LP2975, or a rail to rail opamp with built in reference.

I've searched Newark and Digikey for ldo driver, controller etc. and the LP2975 doesn't even come up! I found it while goggling. They both have them in stock though. They really have to improve there search engines.

Thanks

- B
- Bob Monsen
  
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posted
15 years ago

Wed, May 7, 2008 3:19 AM

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- H
- Hammy
  
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posted
15 years ago

Wed, May 7, 2008 11:16 AM

Thanks Bob

I went with the LP2975 using a FQT5P10 P-Fet as the pass element. Oddly enough this combo is cheaper (less then two bucks) then an LDO with an integrated FET . The few I could find in stock that can be used to my input voltage were all in the 3 to 7 dollar range! The LP2975 has a pretty good reference with current limiting (1 resistor

56mV drop) and low power shutdown. The Quiescent current is low to, unlike the BJT LDO's that can be several mA (base drive for the BJT) even for my modest output current.

It should have been here yesterday along with some other stuff but UPS sent it to the wrong town! I've placed 11 orders now through Newark using the default courier (supposedly the best deal). The default courier is UPS overnight air. Of those eleven orders 2 actually were delivered overnight, three I had to drive to the UPS store to pick-up, because they didn't want to send a driver to my end of town until the next day. The other six were plane delays are other screw-ups like I mentioned. Dealing with these incompetent asses is almost like dealing with the government. By comparison I've placed 10x that amount of orders through Digikey using Purolator. The orders are always here within two days and at the same time of the day, so I know when to be here.