Using REG0 as LDO and REG1 as DCDC

[lemi]

Hi

We are doing some power optimizations. We are currently running the nrf52840 with REG0 as LDO, REGOUT0 to 2.1V and for REG1 the internal DCDC converter. As I see from the datasheet, this combination is not mentioned. The supply of VDDH is around 2.5V.

I am measuring the power consumption by adding a shunt between 2.5V and VDDH. In "System off" mode, i am measuring current peaks around 2.5mA all 60us (ca. 15kHz). This leads to a current offset of around 800uA.

Do you recommend to use the configuration of REG0 as LDO and REG1 as DCDC converter?

Could it be that the errata 197 has an impact event if we do not use the DCDC0?

Does the interal DCDC converter somehow update the voltage with a frequency of 15kHz?

[lemi]

To add some information: This is measured over a 10Ohm resistor, current going into VDDH. VDD has some capacity of course, but no further external peripherial (and there is no ripple which could inidcate some load there).

The software is a simple WFE loop.

int main(void)
{
 
 
    __disable_irq();
    initializeGPIO();
    for (;;) {
        __disable_irq();
        __WFE();
    }
}

[Jared]

Hi,

The product specification only gives examples of different combination not necessarily every possible one. I would generally recommend using DC/DC at both REG0 and REG1 as it more effective then LDO. The drawback of using DC/DC is that it requires an external filter which might not be manageable if you're restricted in area. 

The supply of VDDH is around 2.5V.

 Is there a specific reason that you use High Voltage Mode instead of Normal mode? A supply of 2.5 V is within the range of Normal mode.

 

Could it be that the errata 197 has an impact event if we do not use the DCDC0?

 The errata should only be related to DCDC on REG0. Are you observing any of the symptoms of the errata?

regards

Jared