LD1086DT33TR Dropout voltage query

[Tejas_P_R]

Hi Team,

We are using LD1086DT33TR regulator to generate 3.3V output from 5V input, But the the maximum dropout voltage given in the datasheet is 1.5V.Our dropout voltage is 1.7V (5V - 3.3V =1.7V) which is exceeding the max dropout voltage of the IC mentioned in datasheet ,My question is whether this IC is suitable for our requirement or we need to look for alternative.

Regards

Tejas

[AScha.3]

take another.

need 1,5A really ? maybe this:

https://www.mouser.de/ProductDetail/Diodes-Incorporated/AP7362A-33SP-13?qs=M%2FOdCRO8QQ3CiX1oDLy5Bg%3D%3D

if 1A is ok, take any ...like this:

https://www.mouser.de/ProductDetail/Texas-Instruments/TLV1117LV33DCYR?qs=tEz3BkPb1rwzXMb8FiWhow%3D%3D

[Tejas_P_R]

Hi AScha.3,

 The suggested part is also having a low dropout voltage so it is not meeting my requirement,(VIN=5V,VOUT=3.3, I=1.5A) Dropout voltage should be 1.7V or greater. 

[Vincenzo]

Hi Tejas_P_R,

you are in good position, the dropout value is the minimum input voltage difference from output voltage and input voltage to guarantee the electrical specification of the DS. Just in case you need to pay attention to the power dissipation of the device in case you use the device with higher input voltage (in AMR table=30V). 3.3V on DS is obtained with 6.3Vin.

Best Regards

Vincenzo

[Tejas_P_R]

Hi Vincenzo,

As my requirement is Output voltage should be 3.3V, But as mentioned in datasheet Maximum dropout voltage @ 1.5A load is 1.5V, So if my input is 5V my output will become 3.5 as it crosses 3.3V so I feel this may damage my circuit even if the voltage slight higher than 5V, So could you suggest me the part with 1.7V dropout voltage or more.

Regards

Tejas

[Peter BENSCH · Accepted solution]

Hi @Tejas_P_R,

Unfortunately, you are confusing a few parameters about LDOs (Low-Dropout Regulators): the dropout voltage is the difference between the input voltage and the output voltage. The LDO needs at least this dropout voltage to be able to regulate the output voltage. And for the LD1086 this minimum dropout voltage is typically 1.3V, but can go up to max 1.5V.

In the case of the LD1086DT33, the target output voltage is 3.3V, the input voltage according to your specification is 5V, which results in a voltage difference of 1.7V, which is easily above the required dropout voltage (1.7V > max 1.5V). In your case, the LD1086DT33 can regulate perfectly, even if the input voltage drops to 4.8V.

Clearer now?

Regards
/Peter

[Tejas_P_R]

Hi Peter,

Thank you for the valid answer, I got confused by so many answers which made me to think in a such a way that the dropout voltage is causing the exact output. but now I got clear image.

I was expecting this type of clarity on Dropout voltage. everywhere dropout voltage is mentioned only as difference of input and output voltage but unfortunately not explained as "this dropout is able to regulate the output".

Thanks again for the response and clearing my doubt and confusions...!

Regards 

Tejas