Nordic 3 - Power Supply

5 Hardware description: Smart Remote 3 DK add-on
Doc. ID 4374_139 v1.1
Page 35
• Cut SB20 and SB21
This circuit is a ±250° per sec/±500° per sec/±1000° per sec/±2000° per sec selectable three-axis gyro and a ±2
g/±4 g/±8 g/±16 g selectable three-axis accelerometer.
5.3.5 Power supply
The Smart Remote 3 DK add-on gets its power from two AA batteries or from the nRF5x Development Kit (DK).
The batteries can be alkaline (2 × 1.5 V) or rechargeable NiMH (2 × 1.2 V) batteries. The battery circuit has a
protection diode to avoid reverse current if the USB is connected to the nRF5x DK while batteries are inserted.
D1
1PS79SB30.115
VIO
SB7
+
Bat1
+
Bat2
Figure 22: Battery schematic
Smart Remote 3 has a switch for turning the power on or off for most of the circuits. One transistor is used for
this, which is controlled by the nRF chip on the nRF5x DK. See Figure 23: Power on/off switch on page 35.
The low-power accelerometer is always powered.
VIO
R3
10R
VCC
C4
100nF
+
C1
100
µ
F
1
2
P2
Pin List 1x2
C5
1.0
µ
F
C3
100nF
C2
22
µ
F
Supply filter/Current measurement
Power supply switch
POWER ON/OFF
Q2
FDV304P
Figure 23: Power on/off switch
The voltage from the batteries or nRF5x DK is used unregulated for most part of the design. However, the
trackpad requires a stable voltage of 3.3 V. To achieve this, the trackpad gets the power from a fixed step-up/
step-down charge pump generator that outputs 3.3 V. See Figure 24: Voltage regulator for the trackpad on
page 36.