BTT6020 trigging fault upon power up with load connected

Tip / Sign in to post questions, reply, level up, and achieve exciting badges. Know more

cross mob
lock attach
Attachments are accessible only for community members.
DLEng
Level 1
Level 1
First like given 5 sign-ins First reply posted

Hi,

We are using a BTT6020-1ERA as per the attached schematic to control a small resistive load (max 100W @25V).
During development testing, in which we used an electronic load to substitute the actual load, we found that applying power to the input of the BTT6020 with the load enabled at 4A, would cause the device to go into FAULT mode, with the IS pin going HIGH and remaining that way.  Note though that this only happens over a certain Input voltage... up to approximately 24.2V the device starts up without issue and powers the load.  Beyond this voltage, a FAULT trip occurs as soon as the IN (enable) pin is driven HIGH.  The input voltage this occurs at differs slightly from one PCB to to another (I suspect this is due to component tolerances).
Disabling the load first helps, however it is still sometimes possible for the device to go into FAULT mode, despite the only load being some input capacitance on the otherwise-disabled load.

We have tried replacing a BTT6020-1EKB with a BTT6010-1ERA, and found that whilst the issue is still observed, the input voltage it occurs at increases to around 26V.  

Any assistance with this issue would be greatly appreciated

Regards,

Daniel

 

0 Likes
1 Solution
lock attach
Attachments are accessible only for community members.
Anshika_G
Moderator
Moderator
Moderator
First question asked 50 likes received 250 replies posted

Hi Daniel,

Apologies for the delay.

We have tested the setup with resistive and capacitive load in parallel connection.
It is seen that the device is showing no fault at 470uF but at 690uF. 

Attaching you the file for results.

Please let me know if you have further queries.

Best Regards,
Anshika

View solution in original post

0 Likes
7 Replies
Anshika_G
Moderator
Moderator
Moderator
First question asked 50 likes received 250 replies posted

Hi Daniel,

Your query has been acknowledged. 
To be clearer, please verify:

The IS pin goes into Fault mode when the load is supplies at 4A beyond 24.2 V. The device works without any issue up to 24.2 V.  And when you disable the load while starting, the fault doesn't occur sometimes but sometimes it happens.
Also, on replacing BTT6020-1ERA with BTT6010-1ERA, the device works without any issue up to 26 V. 

If possible, can you share the oscilloscope results for Vs,Vout,IL and Is?

Best Regards,
Anshika

0 Likes
lock attach
Attachments are accessible only for community members.

Hi Anshika

Thankyou for your response.
To confirm:

The IS pin goes into Fault mode when the load is supplies at 4A beyond 24.2 V.
-> Yes

The device works without any issue up to 24.2 V.
-> Yes

And when you disable the load while starting, the fault doesn't occur sometimes but sometimes it happens.
-> Yes. I suspect this is because the input capacitance of the load (Rigol 3031A) is right on the upper limit of what the device can supply above 24.2V without triggering short circuit protection. Turning the load ON adds additional resistive loading to the output of the device and ensures it always fails to turn ON the output at voltages above 24.2V.


Also, on replacing BTT6020-1ERA with BTT6010-1ERA, the device works without any issue up to 26 V.
-> Yes

 

Using the BTT6020 only, I have attached oscilloscope captures of all signals except the Fault line, however I have observed this line without capturing it and confirmed it goes HIGH when the output turns off.

With further investigation today we have found that the issue occurs with output capacitance above approx 500-700uF (at our maximum system voltage of 25.2V), with the DC/resistive aspects of the load having only a small bearing on this (I tested 0-10A). The higher the input voltage, the lower the load capacitance the device can sucessfully turn on with.

I have tested purely resistive loads up to 10A at 26V+ without a problem.

It appears the load capacitance is triggering protection i.a.w. Figure 18 (Section 6.5.1 of the BTT6020-1ERA datasheet), however this is a theory we'd like to confirm with you. The voltage range we have been testing at (24-25V) is right on the knee point of the graph, thus small increases in voltage result in a large decrease in the current limit. The graph suggests the current limit at 24.4V is around 58A, and we observed current spikes upon turn-on which exceeded this level, with higher capacitance values.

This may also explain why the BTT6010-1EKB only appears to exhibit the same behaviour at a higher voltage.

Do you have a specification for the maximum load capacitance Vs input voltage?

Is there a work around to make the device more tolerant of short current spikes, other than to choose a variant with a higher current limit or limit load capacitance?

For the attached oscilloscope captures, we had trouble recording current at the same time as the other signals, as having the other signals connected was creating a large offset on our differential probe (which was connected across an 0.0025ohm shunt). We applied a large calibration offset to the probe settings to correct for this, however for accuracy, please only refer to the current levels recorded in the captures where all other channels remained at zero (as the other probes were disconnected in these captures, and the calibration offset removed):
CH1(yellow) = Vout
CH2(cyan) = Current (scaling is I = V/0.0025, ie. 20A per 50mV)
CH3(purple) = Enable signal
CH4(dark blue) = Vin

thank you,

regards,

Daniel

0 Likes
Anshika_G
Moderator
Moderator
Moderator
First question asked 50 likes received 250 replies posted

Hello,

Thank you for the detailed response.

Can you also please let us know the following details:

VS = tested at 24 and 25 V?
IN = 5V? (any PWM?)
DEN = 5V?

When load is resistive, no issue observed. With capacitive load of 500-700uF only, fault is triggered.

VS is high and den IN will be set to high or other way around? (Timings please)

Is DEN high before IN or with IN?

Best Regards,
Anshika

0 Likes

Hi Anshika,

VS = tested at 24 and 25 V? -->Yes, we stepped through in 0.2V steps from 24V up to 26V to find the point the failure occured with our Rigol 3031A load connected.
IN = 5V? (any PWM?) -->3.3V from an STM32 microcontroller, no PWM.
DEN = 5V? -->Tied to IN (3.3V)

When load is resistive, no issue observed. With capacitive load of 500-700uF only, fault is triggered. -->Yes.

VS is high and den IN will be set to high or other way around? (Timings please) -->VS is HIGH first, followed by DEN and IN approx 250ms later.

Is DEN high before IN or with IN? --> With IN

regards,
Daniel

0 Likes
Anshika_G
Moderator
Moderator
Moderator
First question asked 50 likes received 250 replies posted

Thanks Daniel for the info.

We are doing analysis from our side and will update as soon as I have the results.
Sorry for the delay.

Best Regards,
Anshika


lock attach
Attachments are accessible only for community members.
Anshika_G
Moderator
Moderator
Moderator
First question asked 50 likes received 250 replies posted

Hi Daniel,

Apologies for the delay.

We have tested the setup with resistive and capacitive load in parallel connection.
It is seen that the device is showing no fault at 470uF but at 690uF. 

Attaching you the file for results.

Please let me know if you have further queries.

Best Regards,
Anshika

0 Likes
Anshika_G
Moderator
Moderator
Moderator
First question asked 50 likes received 250 replies posted

Hi Daniel,

Please let me know if you need further support.

Best Regards,
Anshika


0 Likes