droput voltage for LDL1117

[ves011]

I just bought 10 pcs of LDL1117S33R which i plan to use them to power 3.3V modules form a 4V regulated source.

According to the data sheet the typical dropout is 350mV and max is 600mV @1.2A. My module consumes less than 500mA, so i expect to have enough margin with a Vin of 4V to get 3.3V at the ouput. But the module doesnt boot at 4V input.

When measured the dropuout is 1V -  1.1V. Did anybody face this problem?

The chips are labeled LL33 F329 with ST logo

[Andrew Neil]

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@ves011 wrote:

My module consumes less than 500mA

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How is that determined? Is that the average operating current?

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@ves011 wrote:

But the module doesn't boot at 4V input.

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Often the current required to boot is more - sometimes much more - than the operating current ...

[SofLit]

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@Andrew Neil wrote:

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Often the current required to boot is more - sometimes much more - than the operating current ...

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Called "inrush current" : 

https://www.matsusada.com/support/terms/ps/rush-current.html

[ves011]

Here is the boot current captured with power monitor

its 60mA. Later on when WiFi is enabled and communication starts it has spikes of ~500mA

[ves011]

To make it more clear, with 4V input the output is 2.94V which is more than 100mV below the rated output.

[SofLit]

What is the voltage output with no load?

[Andrew Neil]

Show your schematic

[Peter BENSCH · Accepted solution]

@ves011 The max 600mV for the LDL1117 is specified for an input voltage that is at least 1V above the output voltage. With your small voltage difference, I would recommend switching to an ultra-low dropout LDO, e.g. the LD39100PU33R.

Regards
/Peter

[ves011]

when Vin > 4.4V,  Vout is steady 3.369V. I tested it up to 6V

Vin   Vout

4.3 - 3.236

4.2 - 3.138

4.1 - 3.040

4.0 - 2.942

all these on a constant load of ~20mA

[SofLit]

What @Peter BENSCH said confirmed your findings.

4.3 - 3.236 = 1,064V

4.3 - 3.236 = 1,062V

4.1 - 3.040 = 1,06V

4.0 - 2.942 = 1,058V

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