LMV431A: minimum working cathode voltage when ref>1.5v

Hi Sean,

The EC table is set for closed loop regulation mode. If you are using this as a comparator, then minimum Iq does not apply as much because it is open loop and it is not regulating. I would still design around the minimum Iq of the device for regulation stay on the safe side so the 80uA.

-Marcoo

Hi Marcoo:
if it is in open loop with ref voltage more than 1.5V, what would Iq Vs Vka be? or minimum Iq or Vka?

Hi Jun Yin,

When REF > 1.25V, Vka is typically around ~1V, you can use that value to calculate how much current you need for your load/amplifier. Make sure the device has at least 80uA of Iq and you are good. Look at section 10.2 of the TLV431 datasheet for a comparator example. The TLV431 and LMV431 are similar devices so the information is extremely relevant.

-Marcoo

Hi :
that's what I though, while we got quite different Vka value which is above 1.4V when ref=1.9V; with 5V to cathode through 10Kohm, 5V to ref through 200k/300k resistor divider; it a simple test circuit, i can't find anything wrong;

Sean

Hi Sean,

That is odd. Can you try your test again with a 10k ohm resistor in series with the Ref pin after the voltage divider?
If that doesn't work, can you measure the current and voltages at all the pins so I can try on my side?

-Marcoo

Hi Marcoo:

it's LMV431AIMFX/NOPB under test;

test circuit like below; Ika and Iref are calculated by Ika= (V1-VKA)/R3, Iref=(V1-VREF)/R1-VREF/R2;

V1(V)	VKA(V)	VREF(V)	IKA(mA)	IREF(uA)
1	1	0.5	0	0
2	1.977	1	0.023	0
2.5	1.153	1.2486	1.347	0.28
3	1.215	1.496	1.785	0.8
4	1.448	1.966	2.552	6.8
5	1.508	2.133	3.492	73.4

so does LMV431AIMFX/NOPB support open loop mode comparator?

TLVH431B is as good as datasheet like below

V1(V)	VKA(V)	VREF(V)	IKA(mA)	IREF(uA)
1	0.94547	0.5	0.05453	0
2	1.9328	0.99984	0.0672	0.032
2.5	0.909	1.25	1.591	0
3	0.8726	1.463	2.1274	7.4
4	0.87763	1.5473	3.12237	90.54
5	0.879	1.5768	4.121	184.64

Hi Sean,

I will test the lmv431 in open loop in the lab on my side after the holiday are over to verify if I can recommend it as a comparator. Is there a particular reason you would want to use the LMV431 over the TLVH431 or TLV431?

-Marcoo

Hi Marcoo:

no particular reason, it's just alternative part in BOM;

thanks and happy new year;

Sean