ADPD107 datasheet(30/66 Pages) AD

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ADPD105/ADPD106/ADPD107

Data Sheet

Rev. A | Page 30 of 66

TYPICAL CONNECTION DIAGRAM

Figure 34 shows a typical circuit used for wrist-based heart rate

measurement with the ADPD105 WLCSP using a green LED.

The 1.8 V I2C communication lines, SCL and SDA, along with

the GPIO0 and GPIO1 lines, connect to a system

microprocessor or sensor hub. The I2C 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 34 is identical for the ADPD107, except the I2C interface

is replaced by an SPI. There are multiple ways to connect

photodiodes to the 8-channel ADPD105 LFCSP, as shown in

Table 22 and Figure 37. 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, VDD, 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, in an application where a single, large photodiode

is used, the dynamic range can be increased by splitting the current

between multiple inputs. This is achieved by connecting the anode

of the photodiode to multiple channels so that the current can

be 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 just a single channel.

It is important to leave the unused input floating for proper device

operation.

Figure 35 and Figure 36 show the recommended connection

diagram and printed circuit board (PCB) layout for the

ADPD105 and ADPD107, respectively. The current input pins,

PD1-2 and PD3-4, 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.

PD3-4

PDC

PD1-2

LEDX1

VLED

VREF

1µF

AGND

DGND

LGND

0.1µF

DVDD

AVDD

1.8V

10kΩ

1.8V

SCL

SDA

GPIO0

GPIO1

TO DIGITAL

INTERFACE

ADPD105

4.7µF

Figure 34. Typical Wrist-Based HRM Measurement

123

LGND

LEDX2

LEDX3

LEDX1

SDA

SCL

GPIO0

DVDD

DGND

GPIO1

VREF

AVDD

PD1-2

PDC

PD3-4

AGND

Figure 35. ADPD105 Connection and PCB Layout Diagram (Top View)

LGND

LEDX2

LEDX3

LEDX1

GPIO0

GPIO1

MISO

DGND

MOSI

AVDD

AGND

VREF

PD1-2

PDC

PD3-4

SCLK

Figure 36. ADPD107 Connection and PCB Layout Diagram, Dashed Line

Traces From Blind Vias (Top View)

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