6 Current estimation and efficiency report
6.1 DC-DC Supplying to other devices
Below is shown a simplified block of the DC-DC outputs. The VDD_1P8 needs to externally be connected to a PCB track to supply
the power pins and may also be used to supply to other external circuits on the board. The VDD_1P5 is internally connected to
the power management circuit (PMC) and needs to be connected externally through pcb tracks to the radio power pins. For the
complete schematic connection, refer to session “DC-DC Power modes”
DCDC
External
Circuits
Internal peripherals
Radio
PMC
VDCDC_IN
VDD_1P8
VDD_RF1/2/3
VREFH
VDDA
VDD_1
VDD_0
10 µH
DCDC_GND
VDD_1P5
Figure 16. Simplified DC-DC block showing loading scenario
6.2 DC-DC Output Current Capability
For most of the devices in these series, the VDD_1P8 output is designed to provide maximum current drive of 45 mA (when
VDD_1P8 = 1.8 V). Refer to the device-specific data sheet as this limit may not be the same for all devices. Note the output current
specification in either buck and boost modes represent the maximum current the DC-DC converter can deliver to the MCU plus
external circuits. The MCU radio and MCU internal blocks current need to be considered in the current calculation. The maximum
total output power of the DC-DC converter is 125 mW for most devices (Refer to the device-specific data sheet as this value may
be different for specific devices). The remaining energy allowed for external devices depends on the energy consumed by the
internal peripherals.
When DC-DC is in Pulsed mode, the maximum current the VDD_1P8 can deliver to the system is significantly reduced (0.5 mA
for most devices), and, similar as explained above, this current is shared between MCU and external circuits.
For a specific power supply scenario, refer to below Buck mode or Boost mode topics.
NXP Semiconductors
Current estimation and efficiency report
MKW4xZ/3xZ/3xA/2xZ DC-DC Power Management, Rev. 3, 04 June 2021
Application Note
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