SENSIRION SCD4x, Руководство пользователя

Страница: 5 / 22

www.sensirion.com Version 1.1 – April 2021 5/22
2.3 Interface Specifications
The SCD4x comes in an LGA package ( Table 6 ). The package outline is schematically displayed in chapter 4.1. The landing
pattern of the SCD4x can be found in chapter 4.2.
Name Comments
VDD Supply voltage
VDDH
Supply voltage IR source, must
be connected to VDD on
customer PCB
GND Ground contact
SDA I
2
C Serial data, bidirectional
SCL I
2
C Serial clock
DNC
Do not connect, pads must be
soldered to a floating pad on
the customer PCB
Table 6 Pin assignment (top view). The notched corner of the protection membrane serves as a
polarity mark to indicate pin 1 location.
VDD and VDDH are used to supply the sensor and must always be kept at the same voltage, i.e. should both be connected to
the same power supply. The combined maximum current drawn on VDD and VDDH is indicated in
Table 4 . Care should be
taken to choose a low noise power supply (preferably a low-dropout regulator, LDO, with output ripple of less than 30 mV p-p),
which is adequately dimensioned for the relatively large peak currents. Power supply configurations with large transient voltage
drops are to be avoided to ensure proper sensor operation.
SCL is used to synchronize the I
2
C communication between the master (microcontroller) and the slave (sensor). The SDA pin
is used to transfer data to and from the sensor. For safe communication, the timing specifications defined in the I
2
C manual
12
must be met. Both SCL and SDA lines should be connected to external pull-up resistors (e.g. R
p
= 10 k Ω , see Figure 1 ). To
avoid signal contention, the microcontroller must only drive SDA and SCL low. For dimensioning resistor sizes please take bus
capacity and communication frequency into account (see example in Section 7.1 of NXPs I
2
C Manual for more details
10
). It
should be noted that pull-up resistors may be included in I/O circuits of microcontrollers.
Figure 1: Typical application circuit (for better clarity in the image, the positioning of the pins does
not reflect the positions on the real sensor). VDD and VDDH must be connected to each other close
to the sensor on the customer PCB.
12
http://www.nxp.com/documents/user_manual/UM10204.pdf