Datasheet

the shunt reference will draw continuous current through the 200Ω filter resistor (3.3V - 3.0V)/200 = ~1.5mA.
Note that the 1Ω resistor on Pico W (R9) is designed to help with shunt references that would otherwise become
unstable when directly connected to 2.2μF. It also ensures there is filtering even in the case that 3.3V and ADC_VREF
are shorted together (which users who are tolerant to noise and want to reduce the inherent offset may wish to do).
R7 is a physically large 1608 metric (0603) package resistor, so can be removed easily if a user wants to isolate
ADC_VREF and make their own changes to the ADC voltage, for example powering it from an entirely separate voltage
(e.g. 2.5V). Note that the ADC on RP2040 has only been qualified at 3.0/3.3V, but should work down to about 2V.
3.4. Powerchain
Pico W has been designed with a simple yet flexible power supply architecture and can easily be powered from other
sources such as batteries or external supplies. Integrating the Pico W with external charging circuits is also
straightforward. Figure 6 shows the power supply circuitry.
PS=0: PFM mode (default, best efficiency)
PS=1: PWM mode (improved ripple but much
worse efficiency at light loads)
VBUS VSYS
3V3
W L_GPIO 2
W L_GPIO 1
TP1
R2
100 K
1%
M0 60 3
50 mW
L1
1u
C1
47u
6.3V
20 %
M2012
X5R
R10
10K
1%
M0 60 3
50 mW
U2
RT6154AGQ W
VINA
1
GND
2
FB
3
VOUTa
4
VOUTb
5
LX2a
6
LX2b
7
LX1b
8
LX1a
9
VIN10
10
VIN11
11
EN
12
PS/SYNC
13
PGOO D
14
PGND
15
R20
100 K
1%
M0 60 3
50 mW
C20
100 n
6.3V
10%
M0 60 3
X5R
TP4
C2
47u
6.3V
20 %
M2012
X5R
D1
MBR120VLS FT1G
2 1
R21
560 K
1%
M0 60 3
50 mWTP3
J1
690 -005 -298 -48 6
1
2
3
4
5
6 7
8 9
TP2 C21
47u
6.3V
20 %
M2012
X5R
R8
100 K
1%
M0 60 3
50 mW
R1
10K
1%
M0 60 3
50 mW
USB_DM
USB_DP
3V3_E N
Figure 6. The
powerchain of the
Pico W Rev3 board.
VBUS is the 5V input from the micro-USB port, which is fed through a Schottky diode to generate VSYS. The VBUS to
VSYS diode (D1) adds flexibility by allowing power ORing of different supplies into VSYS.
VSYS is the main system 'input voltage' and feeds the RT6154 buck-boost SMPS, which generates a fixed 3.3V output
for the RP2040 device and its I/O (and can be used to power external circuitry). VSYS divided by 3 (by R5, R6 in the Pico
W schematic) and can be monitored on ADC channel 3 when a wireless transmission isn’t in progress. This can be used
for example as a crude battery voltage monitor.
The buck-boost SMPS, as its name implies, can seamlessly switch from buck to boost mode, and therefore can
maintain an output voltage of 3.3V from a wide range of input voltages, ~1.8V to 5.5V, which allows a lot of flexibility in
the choice of power source.
WL_GPIO2 monitors the existence of VBUS, while R10 and R1 act to pull VBUS down to make sure it is 0V if VBUS is not
present.
WL_GPIO1 controls the RT6154 PS (power save) pin. When PS is low (the default on Pico W) the regulator is in pulse
frequency modulation (PFM) mode, which, at light loads, saves considerable power by only turning on the switching
MOSFETs occasionally to keep the output capacitor topped up. Setting PS high forces the regulator into pulse width
modulation (PWM) mode. PWM mode forces the SMPS to switch continuously, which reduces the output ripple
considerably at light loads (which can be good for some use cases) but at the expense of much worse efficiency. Note
that under heavy load the SMPS will be in PWM mode irrespective of the PS pin state.
The SMPS EN pin is pulled up to VSYS by a 100kΩ resistor and made available on Pico W pin 37. Shorting this pin to
ground will disable the SMPS and put it into a low power state.
Raspberry Pi Pico W Datasheet
3.4. Powerchain 12