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Wat does Low 3.2-µA Quiescent Current at 50 mA mean in LDO?

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ericmar

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Hi,

I hv some doubts on the LDO.

Take TI's TPS71533 as an example. Wat does it mean by Low 3.2-µA Quiescent Current at 50 mA? Also, it only mentions the 24-V Maximum Input Voltage but no maximum input current. So wat happen if i pump in, say 15V@3A? Would it blow?

Sorry if i m asking silly question but i just dont know.

Thanks,
Eric Mar
 

LDO question

most LDO has over current protect.
If it blow,it's a mistake of the manufacture.
 

LDO question

data from https://focus.ti.com/docs/prod/folders/print/tps71533-q1.html
Iout(Max)(A) 0.05
Iq(Typ)(mA) 0.0032
Obviosly you can draw current up to 50 mA
"What does it mean by Low 3.2-mA Quiescent Current at 50 mA?"
Actual 3.2 uA it meant if yor load consume current 50 mA, input current = 50mA+3.2uA , It can say ground pin current = 3.2 uA

Added after 2 minutes:

Input current = Output current + 3.2 uA
 

    E

    ericmar

    Points: 2
    Helpful Answer Positive Rating
Re: LDO question

Project_maker said:
data from h**p://focus.ti.com/docs/prod/folders/print/tps71533-q1.html
Iout(Max)(A) 0.05
Iq(Typ)(mA) 0.0032
Obviosly you can draw current up to 50 mA
"What does it mean by Low 3.2-mA Quiescent Current at 50 mA?"
Actual 3.2 uA it meant if yor load consume current 50 mA, input current = 50mA+3.2uA , It can say ground pin current = 3.2 uA

Added after 2 minutes:

Input current = Output current + 3.2 uA
Click to expand...
In tat case, if I got no choice but to feed in 15V@3A, can I use a resistor to limit the current so that the current supplied to this LDO does not exceed 50mA? Would 300Ω resistor enough? 15V/50mA = 300Ω

Thanks,
Eric Mar
 
Re: LDO question

Hi,

How much power is feed to the device is not the problem. You can have 24V at 10 amps availible to feed the device without any problem. When you try and pull more then 50 ma through the device it will either smoke or go into a fold back condition and self limit the current. You should not need to add any limit resitor. If you need or want to add some protection to the circuit maybe you could place a PTC (Positive thermal coefficient) device in the circuit to limit the possible current flow. It acts like a fuse but will rest when the over current condition goes away.

Hope that helps.

dfullmer
 

    E

    ericmar

    Points: 2
    Helpful Answer Positive Rating
Re: LDO question

dfullmer said:
Hi,

How much power is feed to the device is not the problem. You can have 24V at 10 amps availible to feed the device without any problem. When you try and pull more then 50 ma through the device it will either smoke or go into a fold back condition and self limit the current. You should not need to add any limit resitor. If you need or want to add some protection to the circuit maybe you could place a PTC (Positive thermal coefficient) device in the circuit to limit the possible current flow. It acts like a fuse but will rest when the over current condition goes away.

Hope that helps.

dfullmer
Click to expand...
Thanks for ur explanation.

One more question is: if i want to prevent my LDO (or even a transistor) from burning due to over current supply, wat should i do? Should i use the PTC? Isnt the PTC being used like a fuse, which is normally placed at the beginning point from the DC/DC poweri supply or linear regulator?

Thanks,
Eric Mar
 

Re: LDO question

Hi,

Sorry for the long delay in response been busy here. Yes, the PTC is used as a resetable fuse. That was their original design purpose. They tend to be used in low power application. Once you get into amp and not milliamps then fuses tend to return. Many devices can be protected by fuses but it is not a common practice to add them all over a design. Most design engineers make the circuits to be self protective or just trust in the component manufactuers specification. At some point you have to trust something. Good luck.


dfullmer
 

LDO question

how to design a voltage follow
 

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