tcs3771 ETC-unknow, tcs3771 Datasheet - Page 25

• Manufacturer Part Number: tcs3771
• Description: Color Light-to-digital Converter With Proximity Sensing
• Manufacturer: ETC-unknow

LED Driver Pin with Proximity Detection
The LUMENOLOGY r Company
In a proximity sensing system, the IR LED can be pulsed by the TCS3771 with more than 100 mA of rapidly
switching current, therefore, a few design considerations must be kept in mind to get the best performance. The
key goal is to reduce the power supply noise coupled back into the device during the LED pulses.
The first recommendation is to use two power supplies; one for the device V
In many systems, there is a quiet analog supply and a noisy digital supply. By connecting the quiet supply to
the V
capacitor as close as possible to the V
of the LED voltage regulator to supply the 100-mA current surge.
If it is not possible to provide two separate power supplies, the device can be operated from a single supply.
A 22-Ω resistor in series with the V
noise. The previous capacitor placement considerations apply.
V
I
The I
value is a function of the I
at 400 kbps, uses 1.5-kΩ resistors. A 10-kΩ pull-up resistor (R
2
BUS
C bus voltage shown in the Available Options table for the specific device being used.
2
DD
Regulator
Regulator
Regulator
in the above figures refers to the I
C signals and the Interrupt are open-drain outputs and require pull−up resistors. The pull-up resistor (R
Voltage
Voltage
Voltage
pin and the noisy supply to the LED, the key goal can be meet. Place a 1-μF low-ESR decoupling
Figure 16. Proximity Sensing Using Separate Power Supplies
Figure 17. Proximity Sensing Using Single Power Supply
C*
. 22 mF
. 22 mF
2
APPLICATION INFORMATION: HARDWARE
C bus speed, the I
1 mF
DD
1 mF
r
supply line and a 1-μF low ESR capacitor effectively filter any power supply
DD
2
C bus voltage which is either V
22 W
pin and another at the LED anode, and a 22-μF capacitor at the output
www.taosinc.com
1 mF
1 mF
IR LED
IR LED
2
C bus voltage, and the capacitive load. The TAOS EVM running
V
GND
LDR
V
GND
LDR
DD
DD
* Cap Value Per Regulator Manufacturer Recommendation
COLOR LIGHT-TO-DIGITAL CONVERTER
TCS3771
TCS3771
PI
) can be used for the interrupt line.
DD
r
or 1.8 V. Be sure to apply the specified
SCL
SDA
SCL
SDA
INT
INT
with PROXIMITY SENSING
DD
R
R
and the other for the IR LED.
P
P
V
V
BUS
BUS
R
R
Copyright E 2011, TAOS Inc.
P
P
TAOS110A − MARCH 2011
R
R
PI
PI
TCS3771
P
25
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