DRV3901-Q1: DEV_ERR after first trigger

Hi ,

Thanks a lot for the question. To further understand the issue could you help with the following points

1. What is the status of nFAULT in DRV3901-Q1?

2. The load resistor seems to be 30Ohms, typical pyro load is around 2Ohms, is there a reason to test with 30Ohms?

3.. DUring the Pyro triggering is there any disturbance seen in PVDD,VDRV and VDD supplies.

4. Can you provide me the waveform SPI pattern(SCLK,SDO,SDI and nSCS) which is used to confirm the  DEV_ERR.

Thanks,

Ibinu

Hello Ibinu, 

Thank you for your reply. 

Ibinu Alaudeen Nadeera said:

1. What is the status of nFAULT in DRV3901-Q1?

nFAULT signal is low status. we can see " On completion of the deployment (timer completion or abortion due to fault), the device updates the STATUS registers. Further deployment commands are not serviced until a CLR_FAULT command is issued." at datasheet. 

Although the deployment is completed without error, nFAULT signal is low??

Q2~Q4 the customer are checking again, let you know after re-testing. 

Q5. when the customer remove Reservoir capacitor, the DEV_ERR don't occur. Can reservoir capacitor cause DEV_ERR?

Thank you. 

Hello Ibinu, 

I am sorry to push you, Would you please let me know your opinion regarding Q1 and Q1 firstly? 

Q2~Q4 the customer are checking again, let you know after re-testing.

Thank you. 

Hi Dino,

The nFAULT Pin can be asserted LOW after deployment if the DEPLOY_SUM = 3h (Deplyoment completed with warning or aborted with error.) assuming the NFAULT_CONFIG3 is at the default state (1h). 

One possibility for that to happen here is in case the load is 30Ohms as shown in the diagram the current in the load cannot built up to the set current (because the drop across the load will be limiting the current). In such an event TSTART_TO can occur and consequently the nFAULT can be asserted low (Under the above assumption)

However, we can confirm this looking at the STATUS registers after deployment. 

Also, I would recommend testing the driver with an expected load of 2Ohms to be sure.

Thanks,

Ibinu

Hello Ibinu, 

Thank you for your reply. 

As your recommendation, when the customer use 2 ohm load, deployment completed without fault. but this test is progressed without reservoir capacitor. 

When the customer test with reservoir capacitor (10mF), first deployment completed without fault, but the DEV_ERR occur after power reset.

Is there any specification max limit of reservoir capacitor? Can high reservoir capacitor value cause any issue?

Please let me know your opinion. 

Thank you. 

Hi Dino,

Thanks for confirming the results.

There is no limit in the cap value from a device perspective for deployment. However the cap diagnostics can have an impact based on the reservoir cap value.

During the power reset is the customer seeing some voltage glitches in the PVDD(or VDRV) or VDD. Also once the device goes into DEV_ERR how is it recovering?

Thanks,

Ibinu

Hi Dino,

Adding to the above point, can you share a voltage waveform for PVDD,VDRV and VDD while the deployment happens.

Thanks,

Ibinu

Hi Ibinu, 

Thank you for your quick response. 

Ibinu Alaudeen Nadeera said:

Also once the device goes into DEV_ERR how is it recovering?

After discharge reservoir capacitor, power reset again and it is recovered. 

I requested a voltage waveform but I didn't get yet. 

Is there any equation to fix reservoir capacitor value? 

The customer would like to reduce reservoir capacitor value to 7000uF and will test again. 

Thank you. 

Hi Dino,

Please find an excel calculator for the VREG cap calculation2746.VREG_CAP.xlsx

Thanks,

Ibinu

2746.VREG_CAP.xlsx