# TL431, LM431, KA431, TL1431 like stability

G

#### Glenn

Jan 1, 1970
0
(Answers are sent to news://sci.electronics.components )

I have been a little curious about the temperature versus stability - so
I compared two datasheets:

Unconditionally stable 0..100mA: Below 6nF - or more than 3uF:
http://www.ti.com/lit/gpn/tl431

Unconditionally stable 0..100mA:
<7pF
or
3nF < CL < 25nF
or
http://www.diodes.com/datasheets/TL431_432.pdf

-

What do I find?

(1) That the stability curves (possible capacitance loads) is different
for different suppliers, and

(2) that the stability is only shown for Ta=25 deegree Celsius.

This means:

(1) It is harder to find an unconditionally stable capacitance load
intervals for all suppliers (only 2 datasheets used in comparison).

(2) You do not know if it is stable - or how to make it stable - at e.g.
Ta -40 deegree Celsius

How do you stably use and select __431?

-

How do capacitor ESR and ESL influence stability?

Glenn

J

#### Jamie

Jan 1, 1970
0
Glenn said:
(Answers are sent to news://sci.electronics.components )

I have been a little curious about the temperature versus stability - so
I compared two datasheets:

Unconditionally stable 0..100mA: Below 6nF - or more than 3uF:
http://www.ti.com/lit/gpn/tl431

Unconditionally stable 0..100mA:
<7pF
or
3nF < CL < 25nF
or
http://www.diodes.com/datasheets/TL431_432.pdf

-

What do I find?

(1) That the stability curves (possible capacitance loads) is different
for different suppliers, and

(2) that the stability is only shown for Ta=25 deegree Celsius.

This means:

(1) It is harder to find an unconditionally stable capacitance load
intervals for all suppliers (only 2 datasheets used in comparison).

(2) You do not know if it is stable - or how to make it stable - at e.g.
Ta -40 deegree Celsius

How do you stably use and select __431?

-

How do capacitor ESR and ESL influence stability?

Glenn

That is the difference between Mill spec. and home entertainment
components.

The price also reflects that, too.

P.S.

When designing for critical operations or customers, you normally
fully test each batch and cat it. Also, make previsions in the design
and assemblies to compensate for each unit in the final test.

Jamie

G

#### Glenn

Jan 1, 1970
0
On 29/04/12 15.14, Phil Hobbs wrote:
....
That's a good reminder that just because two chips have the same part
number doesn't mean they behave the same way, especially under unusual
conditions.

The TL431 is pretty slow, so ESL shouldn't be a big worry. (You're
going to be using SMT ceramics, I assume.) The simple method is to bomb
it flat with a 10 uF X7R ceramic and not worry about it any more.
(The 431 is a nasty noisy beast anyway, so filtering hard is all to the
good.)

Cheers

Phil Hobbs

I have compared TL431 with some other ballast-regulators, but they do
not have much lower noise?

How low "can" the noise reasonably be?

How low will a "standard" ca.0.4W 9.1V zener diode at 10mA e.g. be for
comparison?

Is this the state of the art ballast-regulators regarding long-term
stability (pretty expensive)? No noise level is given as far as I can read:
LT1019A 5V:
http://search.digikey.com/us/en/products/LT1019ACS8-5#PBF/LT1019ACS8-5#PBF-ND/889569
LT1019A 2.5V:
http://search.digikey.com/us/en/products/LT1019ACS8-2.5#PBF/LT1019ACS8-2.5#PBF-ND/888648

http://www.linear.com/docs/3834
Quote from datasheet: "...
If output bypassing is desired to reduce high frequency output
impedance, keep in mind that loop phase margin is significantly reduced
for output capacitors between 500pF and 1Î¼F if the capacitor has low ESR
(Effective Series Resistance). This can make the output â€œringâ€ with
deliberately adding a resistor to increase ESR as shown in Figure 1.
...."

-

I have found this noise cancelling circuit, but it will ruin the voltage
stability:

Finesse Voltage Regulator Noise!:
http://www.wenzel.com/documents/finesse.html

br

Glenn

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