Datasheet
Data Sheet ADPD1080/ADPD1081
Rev. B | Page 31 of 74
APPLICATIONS INFORMATION
TYPICAL CONNECTION DIAGRAM
Figure 36 shows a typical circuit used for wrist-based heart
rate measurement with the ADPD1080 WLCSP using a green
LED. The 1.8 V I
2
C communication lines, SCL and SDA,
along with the GPIO0 and GPIO1 lines, connect to a system
microprocessor or sensor hub. The I
2
C signals can have pull-up
resistors connected to a 1.8 V or a 3.3 V power supply. The
GPIO0 and GPIO1 signals are only compatible with a 1.8 V
supply and may need a level translator. The circuit shown in
Figure 36 is identical for the ADPD1081, except the I
2
C
interface is replaced by an SPI. There are multiple ways to
connect photodiodes to the 8-channel ADPD1080 LFCSP, as
shown in Table 22 and Figure 39. The photodiode anodes are
connected to the PD1 to PD8 input pins and the photodiode
cathodes are connected to the cathode pin, PDC.
Provide the 1.8 V supply, V
DD
, to AVDD and DVDD. The LED
supply uses a standard regulator circuit according to the peak
current requirements specified in Table 3 and calculated in the
LED Driver Pins and LED Supply Voltage section.
For best noise performance, connect AGND, DGND, and
LGND together at a large conductive surface, such as a ground
plane, a ground pour, or a large ground trace.
The number of photodiodes or LEDs used varies depending on
the application as well as the dynamic range and SNR required.
For example, when using a single, large photodiode in an
application, split the current between multiple inputs to increase
the dynamic range. By connecting the anode of the photodiode
to multiple channels, the current can split evenly among the
number of channels connected, effectively increasing the dynamic
range over a single channel configuration. Alternatively, in
situations where the photodiode is small or the signal is greatly
attenuated, SNR can be maximized by connecting the anode of
the photodiode to a single channel. It is important to leave the
unused input floating for proper device operation.
Figure 37 and Figure 38 show the recommended connection
diagram and printed circuit board (PCB) layout for the 16-ball
WLCSP ADPD1080 and 17-ball WLCSP ADPD1081, respectively.
The current input pins, PD1 and PD5, have a typical voltage of
1.3 V during the sampling period. During the sleep period,
these pins are connected to the cathode pin. The cathode and
anode voltages are listed in Table 3.
PD5
PDC
PD1
LEDX1
VLED
VREF
1µF
AGND
DGND
LGND
0.1µF
0.1µF
DVDD
AVDD
1.8V
10kΩ 10kΩ
1.8V
SCL
SDA
GPIO0
GPIO1
TO DIGITAL
INTERFACE
ADPD1080
4.7µF
16110-036
Figure 36. Typical Wrist-Based HRM Measurement
1 2 3
A
B
C
D
E
F
LGNDLEDX2
LEDX3 LEDX1
SDA
SCL GPIO0 DVDD
DGND
GPIO1 VREF AVDD
PD5 PDC PD1
AGND
16110-037
Figure 37. ADPD1080 Connection and PCB Layout Diagram (Top View),
16-Ball WLCSP
1 2 3
A
B
C
D
E
F
LGNDLEDX2
LEDX3 LEDX1
GPIO0
GPIO1
MISO
DGND
MOSI
AVDD
AGND
VREF
PD5 PDC PD1
SCLK
CS
16110-038
Figure 38. ADPD1081 Connection and PCB Layout Diagram, Dashed Line
Traces from Blind Vias (Top View), 16-Ball WLCSP
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