nPM2100 Behavior with LDO in Ultra-Low-Power Mode

[bdub94]

I have a couple of questions regarding the operation of the nPM2100 when using the LDO in Ultra-Low Power (ULP) mode, both in active and hibernate states.

1. Active Mode with Boost in Auto, LDO in ULP:

   • Let’s assume the device is in active mode, the boost is in auto mode, and the LDO is configured in ultra-low-power mode. A small load is connected to the LDO output.

   • According to the electrical specification (Table 12, datasheet v1.0), the maximum output current for the LDO in ULP mode is 2 mA.

   • My question: if the load exceeds 2 mA, what is the expected behavior? Will the LDO output simply droop, or does the device employ any form of current limiting/shutdown behavior?

2. Hibernate Mode with Boost in ULP and LDO in ULP:

   • Now consider the device in hibernate mode, where the boost is forced into ultra-low-power operation. The LDO is configured to remain enabled (in ULP) with a small load connected at its output.

   • If this load exceeds the LDO’s maximum output current in this condition, what happens? Will we just see droop on the LDO output? Could this cause droop on VINT, given that the boost is constrained in ULP mode?

[Menon]

Hello,

Active Mode with Boost in Auto, LDO in ULP:

• Let’s assume the device is in active mode, the boost is in auto mode, and the LDO is configured in ultra-low-power mode. A small load is connected to the LDO output.

• According to the electrical specification (Table 12, datasheet v1.0), the maximum output current for the LDO in ULP mode is 2 mA.

• My question: if the load exceeds 2 mA, what is the expected behavior? Will the LDO output simply droop, or does the device employ any form of current limiting/shutdown behavior?

• If the load exceeds 2 mA while the LDO is in ULP mode, the output voltage will start to drop. The RON of the pass FET is approximately 40 Ω in ULP mode, which can be used to estimate the voltage droop with increasing load.

  Hibernate Mode with Boost in ULP and LDO in ULP:

  • Now consider the device in hibernate mode, where the boost is forced into ultra-low-power operation. The LDO is configured to remain enabled (in ULP) with a small load connected at its output.

  • If this load exceeds the LDO’s maximum output current in this condition, what happens? Will we just see droop on the LDO output? Could this cause droop on VINT, given that the boost is constrained in ULP mode?

• In hibernate mode with the boost in ULP and the LDO enabled in ULP, the LDO output will again start to droop if the load exceeds its maximum output current. However, since the boost converter’s current capability in ULP mode is higher than that of the LDO, there is no concern from the boost side.

kind Regards,

Abhijith

[bdub94]

Many thanks Abhijith.

For context, I'd like to power my device (nRF54L15 + a sensor AFE) with the nPM2100, but through the LDO rather than the boost output in order to have a more stable power supply. This is where my previous questions were coming from.

Given your answers to my previous questions, it's clear that the large RON of the LDO in ULP mode will result in a less stable supply in the event of large current spikes, e.g., BLE comm. spikes. Note that I'm looking to avoid powering the nRF54L15 and the sensor AFE with separate supplies.

As follow up questions:
1. Is it possible to have the LDO in auto mode while the system is in hibernate mode?
2. Alternatively, is it possible to drain Vout while keeping the system in active mode (boost in auto mode / LDO in auto mode)

Any advice here is much appreciated!

[Menon]

Hello,

1. LDO auto mode means that the LDO operation mode follows the PMIC operation mode, not the load. If auto mode is selected, the LDO will be in HP mode when the nPM2100 is in the active state, and in ULP mode when it is in hibernate state. Therefore, the LDO operation mode will be ULP in hibernate state. Note that the LDO quiescent current from the battery in HP mode is 1.9 mA, so you will want to minimize the time spent in this mode.
2. By “drain the VOUT”, do you mean “shut down the VOUT”? That is not possible. The internal load switch between VINT and VOUT is controlled by a state machine, and there are no user controls for it.

Kind Regards,

Abhijith