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Ugly 75L05C

Now the one i tested was made recently by TI.

Ugly #1: oscillates like a banshee without bypassing; the datasheet does not specifically state bypassing is required. Am not too surprixed as most 3-term regulators do require bypassing - but in the cases that do require bypassing, the datasheet says so and also specifies minimum values.

Ugly #2: draws up to 38mA before it *SNAPS* into regulation.

IN ---------- OUT o--+---| 75L05C |---+--+--o Where 100u=Cin, 0.22u=Cout. | ---------- | | --- | --- \\ Rl=1K --- GND --- / | | | GND GND

Case #1: Drive IN, measure Iin, Vin, Vout. No current until about 1.32V rising linearly to about 5mA at Vin=1.64V; gets steeper to about 20mA at 2.06V, decerasing in slope to about 30mA at 3.10V then to about 38mA at 4.64V "flattening" to about

37mA at 4.87V. *SNAP* near 5.00V above which Iin=6.2mA (@ Vin=5.19V, Vo=5.03V); Iin increases near Vin=5.50V to Iin=7.0mA at Vin=20.0V (Vo=6.25V).

Case #2: Drive OUT, measure Vout, Vin and current drawn. Essentially the same (!) except add 1mA/V. Seems that Vin=Vout from 0.5V to about 4.85V with Idraw to 36mA;

*SNAP* to Vout=5.0 at 5.3mA and Vin=4.5V.

Nice work of "low power" LDO!

Reply to
Robert Baer
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All LDO regulators seem to like being heavily bypassed. Actually you should add a little more to supress oscillation at lower temps, Depending upon the type of bypass cap of course. Lytics are the worst.

Cheers

Reply to
Martin Riddle

"Martin Riddle"

** The 78L05 is not an example of a LDO regulator.

And the data sheet is very clear about the need for a 0.1uF bypass on the output.

.... Phil

Reply to
Phil Allison

Got a link to the datasheet? Or did you mean 78L05 ?

Ed

Reply to
ehsjr

Larger Cout? Minimum recommended value please?

Reply to
Robert Baer

Sorry about that; it is the TL750L05C, and the TI databook does not make it clear that bypassing is required. All it states is "All characteristics are measured with a 0.1uF capacitor across the input and a 10uF capacitor, with equivalent series resistance of less than 1 ohm, across the output." . That large cap at the output undoubtely is a large reason for the low output noise spec...

Still, that large current draw before 5V is a bit nasty...and that

*SNAP* at rating is a bit of a jolt...
Reply to
Robert Baer

Yes, i goofed; it is the TL750L05C i measured.

Reply to
Robert Baer

There is a graph on page 6 showing stable unstable regions for ESR values.They recomend a 10uf tant cap esr greater then 0.024 ohms less then 0.4 ohms.

Reply to
Hammy

By the way that is a pretty sparse data sheet. They don't state whether it is a PMOS or BJT LDO. I'm guessing it is a PMOS because they link to this data sheet "Fundamental Theory Of PMOS Low-Dropout Voltage Regulators" in the product folder.

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If you don't need the full 150mA capability you could look at the MCP1791T-5002E.

PMOS LDO well characterised in the datasheet fixed 5V out wide input range 6 to 30V,70 mA output,thermal and foldback protection.

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Data sheet.

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I just got some of these I'm going to be testing them today.

Reply to
Hammy

Me again forgot to add it's stable with ceramic caps :)

Reply to
Hammy

On a sunny day (Wed, 22 Jul 2009 19:03:23 -0700) it happened Robert Baer wrote in :

Never seen one used without bypasing. I use 10uF :-)

Reply to
Jan Panteltje

It's more than a bypass.

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Did you read this paragraph?

"The TL750L, TL751L series are low-dropout regulators. This means that capacitance loading is important to the performance of the regulator because it is a vital part of the control loop. The capacitor value and its equivalent series resistance (ESR) both affect the control loop and must be defined for the load range and temperature range. Figure 1 shows the recommended range of ESR for a given load with a 10-uF capacitor on the output"

See the following graph illustrating the 'tunnel of death' characteristic typical of LDOs. Note that it is potentially unstable with a ceramic output capacitor (very low ESR).

Best regards, Spehro Pefhany

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Reply to
Spehro Pefhany

Is not that tpical of a bad design? 'This capacitor is too good for this chip' LOL

Reply to
Jan Panteltje

Of course you could always put an 0.025 ohm resistor in series with the output, and use any cap you like.

Cheers

Phil Hobbs

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Reply to
Phil Hobbs

Really thin PCB trace of sufficient length?

Reply to
Joel Koltner

That like driving on ice with the hand-brake slightly pulled because the traction control electronics don't work too good :-)

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Reply to
Joerg

And I bet that range is not guaranteed data. On many of my projects I wouldnt' even be allowed to use something like that unless guaranteed. On all the others it would make me lose sleep at night so I just never use LDO chips.

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Reply to
Joerg

I'm told the ABS brakes on some vehicles get fooled when one wheel is on a (slippery) wet manhole cover or streetcar track. In a bad way.

Reply to
Spehro Pefhany

CHEAP systems!

...Jim Thompson

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Reply to
Jim Thompson

Page six in a one page spec? Where are you looking?

Reply to
Robert Baer

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