Buck Regulator Iq and 100% Duty Cycle

[Henry_HP]

Hi,

I've some questions on nPM1100's buck regulator

1) What is the Iq (quiescent current)?

2) Does it support 100% duty cycle?

3) What will happen to VOUTB if VINT < [VOUTB(selected) + Vdropout_buck]?

Regards,

Henry

[Stian Røed Hafskjold]

Hello

1) Iq can be found here: https://infocenter.nordicsemi.com/topic/ps_npm1100/product_overview.html?cp=6_0_0_2_8#sys_el_param

2) I believe you are wondering if the dropout voltage can be close to 0? Drop out voltage is at 0.41V minimum: https://infocenter.nordicsemi.com/topic/ps_npm1100/chapters/core_components/buck/doc/frontpage.html?cp=6_0_0_5_2_3#elec_param

VDROPOUT_BUCK

Dropout voltage, V(VOUTB) - VINT

-

0.41

V

3) The VOUTB will follow the VIN voltage minus the dropout voltage, below the specified VOUTB voltage. For BUCK to supply the desired output voltage, VINT must be V_{DROPOUT_BUCK} greater than the voltage on VOUTB.

https://infocenter.nordicsemi.com/topic/ps_npm1100/chapters/core_components/buck/doc/frontpage.html?cp=6_0_0_5_2_0#output_voltage_selection

Best regards,
Stian

[Henry_HP]

Hi Stian,

Regarding my questions 2 & 3, some buck converters can support 100% duty cycle. If Vin <= (Vout-selected + Vdropout), the regulator is turned off and output pin is directly connected to input pin through high-side MOSFET. 

In this case, Vout = Vin - Vdropout - Vinductor. This feature allows the buck converter continues to supply current to the load although Vin is too low to maintain regulation.

From you reply (3), can I say that nPM1100 does support 100% duty cycle operation?

[Stian Røed Hafskjold]

Hello, yes that is correct. It does not support 100% duty cycle operation in that sense.