Power supply for nRF5340 + nRF7002 combination for very low power consumption

[ValentinKunti]

Hello,

We are currently evaluating a very low power application using the nRF5340+7002. Our hardware design includes a complex power supply configuration, and we need to interface the nRF5340 with 3.3V GPIO levels while potentially using a lower VDDH supply.

Example of our Power Supply Configuration:

• TPS2117 for switching between USB (with 3V regulator) and Vbat (supercap system)
• VCC in battery mode: 2.7V to 2.4V (depending on battery level)
• Host + WiFi connection in High Voltage Mode
• VCC directly powers the nRF5340
• VREG powers VDD and IOVDD of the 7002
• 7002 is powered by 3.3V rail controlled by the 5340

Requirements: We need to configure GPIO levels with VREGHVOUT at 3.3V to control other board components. However, since VCC ranges from 2.7V to 2.4V, this appears impossible in LDO mode due to the constraint: "The maximum output voltage from this stage is given as VDDH - VREGHDROP."

Questions:

1. If we configure VREG in DC/DC mode instead of LDO mode, is it possible to achieve VREGHVOUT = 3.3V with a lower VDDH?
2. An alternative approach would be to connect the nRF5340 to 3.3V instead of VCC, switching to 3.3V only when needed and using VCC with passthrough on the 3.3V regulator for all other cases. Will the nRF5340 tolerate the voltage drops and spikes during VCC to 3.3V transitions since the core works at 1.2V?

Thank you in advance for your assistance.

Best regards,
Valentin Künti

[Simonr]

Hi Valentin

1. This will not be feasible, as VDDH will always be VREGHVOUT will always be VDDH -0.3V no matter what regulator you're using.

2. This should work just fine. We'd recommend not having a very hard transient between the 3.3V and VCC level, as we don't recommend large step increases in supply voltage (more than 0.3V) with very short rise times.

Also, please note that the VDDH input voltage range is 2.5V to 5.5V, so if you expect the battery to run down to 2.4V, it will stop running before the battery is completely empty in VDDH mode. Switching to VDD at low battery levels might be an option, but then you'd lose out on the output supply voltage.

Best regards,

Simon