TMD27721 Datasheet, PDF (28/35 Pages) TEXAS ADVANCED OPTOELECTRONIC SOLUTIONS – DIGITAL ALS and PROXIMITY MODULE

TMD2772
DIGITAL ALS
and PROXIMITY MODULE
TAOS147E − DECEMBER 2012
APPLICATION INFORMATION: HARDWARE
LED Driver Pin with Proximity Detection
In a proximity sensing system, the included IR LED can be pulsed 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. Averaging of multiple
proximity samples is recommended to reduce the proximity noise.
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 LEDA pin, the key goal can be met. Place a 1-μF low-ESR decoupling}
capacitor as close as possible to the V_DD pin and another at the LEDA pin, and at least 10-μF of bulk capacitance
to supply the 100-mA current surge. This may be distributed as two 4.7 μF capacitors.
a _VBUS
v _Voltage
Regulator
ill ^C*
1 mF
LEDK
V_DD
LDR
GND TMD2772 _INT
R_P
R_P
R_PI
t _Voltage
AG ^{t s Regulator}
. 10 mF
1 mF
LEDA
SCL
SDA
* Cap Value Per Regulator Manufacturer Recommendation
s ^{n Figure 13. Proximity Sensing Using Separate Power Supplies}
m ^{te 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_DD supply line and a 1-μF low ESR capacitor effectively filter any power supply
a ^{n noise. The previous capacitor placement considerations apply.}
o _Voltage
l ^{c Regulator}
. 10 mF
22 W
1 mF
LEDK
V_DD
LDR
GND TMD2772 _INT
V_BUS
R_P
R_P
R_PI
ica1 mF
LEDA
SCL
SDA
n_{Figure 14. Proximity Sensing Using Single Power Supply}
ch _{VBUS in the above figures refers to the I}2_{C bus voltage which is either VDD or 1.8 V. Be sure to apply the specified}
I²C bus voltage shown in the Available Options table for the specific device being used.
e_{The I2C signals and the Interrupt are open-drain outputs and require pull−up resistors. The pull-up resistor (RP)}
Tvalue is a function of the I²C bus speed, the I²C bus voltage, and the capacitive load. The TAOS EVM running
at 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
Copyright E 2012, TAOS Inc.
r
www.taosinc.com
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