TCS3771 Datasheet, PDF (26/33 Pages) ams AG – COLOR LIGHT-TO-DIGITAL CONVERTER with PROXIMITY SENSING

TCS3771
COLOR LIGHT-TO-DIGITAL CONVERTER
with PROXIMITY SENSING
TAOS110A − MARCH 2011
APPLICATION INFORMATION: HARDWARE
LED Driver Pin with Proximity Detection
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_DD and the other for the IR LED.
In many systems, there is a quiet analog supply and a noisy digital supply. By connecting the quiet supply to
lid ^{the VDD pin and the noisy supply to the LED, the key goal can be meet. Place a 1-μF low-ESR decoupling}
capacitor as close as possible to the V_DD pin and another at the LED anode, and a 22-μF capacitor at the output
of the LED voltage regulator to supply the 100-mA current surge.
V_BUS
a _Voltage
v _Regulator
till ^Voltage
G _s ^Regulator
C*
. 22 mF
1 mF
1 mF
IR LED
V_DD
R_P
R_P
R_PI
GND TCS3771 _INT
LDR
SCL
SDA
* Cap Value Per Regulator Manufacturer Recommendation
A ^t _{Figure 16. Proximity Sensing Using Separate Power Supplies}
s _{en If it is not possible to provide two separate power supplies, the device can be operated from a single supply.}
m ^{t A 22-Ω resistor in series with the VDD supply line and a 1-μF low ESR capacitor effectively filter any power supply}
noise. The previous capacitor placement considerations apply.
a _{on Voltage}
c ^Regulator
. 22 mF
22 W
1 mF
V_BUS
V_DD
R_P
R_P
R_PI
GND TCS3771 _INT
ical ^1mF
IR LED
LDR
SCL
SDA
n_{Figure 17. Proximity Sensing Using Single Power Supply}
h _{VBUS in the above figures refers to the I2C bus voltage which is either VDD or 1.8 V. Be sure to apply the specified}
c _I2_{C bus voltage shown in the Available Options table for the specific device being used.}
eThe I²C signals and the Interrupt are open-drain outputs and require pull−up resistors. The pull-up resistor (R_P)
value is a function of the I²C bus speed, the I²C bus voltage, and the capacitive load. The TAOS EVM running
Tat 400 kbps, uses 1.5-kΩ resistors. A 10-kΩ pull-up resistor (R_PI) can be used for the interrupt line.
The LUMENOLOGY r Company
r
r
www.taosinc.com
Copyright E 2011, TAOS Inc.
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