TPS2066: Output pin loading issue

Hi,

This two cases are weird.
1. Output should come back when load returns to normal state. Can you confirm the load really return to normal? What's the load at this time.
2. You are correct, this two individual should not influence each other. It sounds incredible, can you attached your schematic?

Regards,
Bob

Hello Bob,

Please find the attach schematic of the switch

the load on EX-3.3V is 100uF capactive load which are mostly ceramic capacitors, the steady state current is 500mA.

Load on SSD_3.3V is M2.SATA which is 75mA

we have tried some modifications to make the switch work

1. We have shorted both the Enables pin and pin 4, and shorted both the outputs ie pin 7 and pin 6, to distribute the inrush current, still it failed.

2. In the above condition itself, we have connected a local charge reservoir of 150uF/16V tantalum, so that this cap first charges up and then delver the inrush for the different circuits, but it still failed.

3. After restoring the circuit to original condition, we tried to turn on the EX_3.3V after SSD_3.3V by giving a delay of 6 secs, still both failed.

4. We have reduced the capacitive load on EX-3.3V by half, still the failure was observed.

After these many changes still the EX-3.3V stucks up at 1V odd at power ON and even after waiting for endless duration it doesn't rises up to 3.3V

One request Bob can we have the further communication on email instead of forum?

Hi, Prashant,

I am still not very clear about your set up, see my question below.

1.It is found that in some cases, when the switch is turned ON, the transient load on EX_3.3V is making its output to go low ie it remains on ~1V and doesn’t comes back even if the load returns to normal state.

[Bob]From your description, the normal state load is 500mA peripherals of processor, correct? So what's the transient load? How the load transient? I want to know what caused Vout drop. TPS2066 current limit point is 1.5A, only when current is limited, do Vout drop to Ios*Rload(limited current*Load resistance). If the load return back to normal, the Vout should return back to normal too, unless Vin is pull to ~1V too or part is damaged(rds is too high).

IN summary, the possible reason for this might be:

1. The part current is still limited when you return back the load to normal state. Please use current probe to check the output current or you can use other way to check output current if current is still limited.

2. Vin is pull down by load. What's the power supply for Vin? Can you check if the Vin voltage is still 3.3V and what's the voltage of SSD_3.3V?

3. Part have problem. If Vin is 3.3V and current is not limited, I suggest you to test Rds(Vds/Ids). If the Rds is higher than Rds(on), the part might have some problems. If the part do have problems, we can figure out what's wrong with the part.  

2.The second part of the issue observed is as the EX_3.3V goes OFF, it also make the SSD_3.3V to also OFF, which should not be case as two individual switches are implemented in the chip.

[Bob]How do you make EX_3.3V goes OFF. Is this same issue with last one or not? 

1. If this same issue with last one, I think the Vin is pulled down because these two channel share one power supply.

2. If it's not same issue with last one and you set enable pin to turn off EX_3.3V which make the SSD_3.3V turn off too, I will think there's some problem with the part. I will test on bench to double confirm and let you check your part, or I can ship you some parts to verify.

Regards,
Bob

Hello Bob,

Output 2 of TPS2066 has a distributed load of approx. 100uf capacitors ( mostly Decaps ), these capacitors will come in picture when enable goes high, the output 2 should goes high and deliver 3.3V, but in this case the output 2 is stuck at 1V, and this doesn't returns back to 3.3V.

secondly there is no drop in Vin which is 3.3V, when the EX_3.3V drops.

as you said will check the current and let you know.

Hi, Prashant,

What do you mean " a distributed load of approx". I hope to verify your test with EVM here. So I want to make my bench same as yours.

Tell me when you checked the result, then we can go to next step. Besides, I have requested a friendship with you on E2E, we can have quick conversation on the case and you can share me some material about your test set up.

Regards,
Bob

Hi, Prashant,

How is your issue, have you find the cause?

Regards,
Bob