Confusion about LDO & supply voltage BLE SWITCH001 GEVB


I was measuring the current consumption and voltage levels on the BLE SWITCH001 GEVB.
In the datasheet the LDO regulator (NCP170 3.3V version) for the RSL10 supply voltage (VBAT) is specified with 2.2V-5.5V input voltage. But when I measured the VBAT power supply voltage and the VIN voltage I noticed that the LDO still works with VIN down to 1.5 V (see screenshot below, it shows only a single pulse by pressing the harvester but not releasing it.). I was wondering how this is possible?

Is the LDO necessary? My measurements indicate that the voltage of the harvester is around 3.6V and the voltage difference of VBAT and VIN is only the dropout voltage. Is there a way to bypass the LDO since in the circuit diagram it seems like there is the possibility to insert a 0 Ohm resistor (R1)? If yes where can I find the location to bypass the LDO on the PCB? I feel like the LDO consumes energy (without serving a purpose?) that could be passed directly to the RSL10.
Maybe you have an explanation and I am missing out on something :slight_smile:

Hello @j.heinzmann,

This is from the first paragraph in the NCP170;

The ultra-low consumption of typ. 500 nA ensures long battery life and dynamic transient boost feature improves device transient response for wireless communication applications.

The LDO helps to suppress the transient response from the RSL10 radio turning on and off. This works to reduce the peak voltage, but it also compensates for the drop we would expect to see when the current suddenly increases.

The circuit would likely work without the LDO. However, it will make it more susceptible to “brown outs” when the radio is switched on, as well as damage from exceeding it’s maximum supply voltage.

If you are interested in more information on the NCP170, you can contact our technical support team.