Initial surge current nRF52832

[Lakshmikanth Satyavolu]

Hi,

I am using TPS61021DSG in my design which is a data acquisition system using nRF52832 BLE module. I am using 1.4V Zinc-air battery to power up my circuit to generate 3VDC at output. 

The circuit not being powered up when using Zinc-air 1.4V. After I investigate more by testing it with DC power supply, I realized the initial current when we apply 1.4V to the circuit goes upto 53mA and settles down at 20mA which is causing my battery to not support that initial surge. 

Attached is my power supply section and the video I have captured which explains the scenario. Can someone please review the design and help me understand why is this happening? 

Best

Lakshmikanth

[ketiljo]

The inrush current is the large 100 µF cap charging up. But there must be something else that draws a lot of current constantly that leads to the 20 mA draw.

[Lakshmikanth Satyavolu]

Hi, 

Could someone please look into it?

What exactly is causing initial surge in the current? We removed MOSFET and tested with a load switch in place of it. Also we removed the entire power section in the circuit and powered the circuit directly. Still the inrush current is being observed. it seems this current is from either firmware or any other internal hardware. 

How can we confirm where it is coming from? I am using SDK16 BLE HRS example as my reference code. 

Any help would be highly appreciated. 

Best

Lakshmikanth. 

[ketiljo]

The large caps will cause inrush current that can't be avoided. Even if you remove the 22 µF, there are a few large (> 1 µF) caps left that's needed for the regulators to function properly.

The CPU will be on for a few ms after startup. This draws some 3-7 mA at 3 V, so maybe 20 mA at 1.4 V is correct, depends on the boost regulator. 

If you set the device into system off  mode, you need something external to wake it up again, GPIO, NFC etc. The device will then start from reset. 

[Lakshmikanth Satyavolu]

Hi Ketiljo,

Thanks for exploitation. I'm bit confused about system OFF mode. 

How to set system OFF mode even before it starts? I mean is there any way we can program the device before it gets powered up, like by asserting a PIN or something like that? 

Best

Lakshmi