TMD37827 datasheet(27/34 Pages) AMSCO

27 / 34 page

Datasheet - Mar. 2013 - V2

TMD3782 – 27

In a proximity sensing system, the IR LED can be pulsed by the

TMD3782 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. If Vbat does not exceed the maximum specified LDR pin

voltage (including when the battery is being recharged), LEDA

can be directly tied to Vbat for best proximity performance.

In many systems, there is a quiet analog supply and a noisy

digital supply. By connecting the quiet supply to 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

VDD pin and another at the LED anode, and a 10 - 22μF bulk

capacitor at the output of the LED voltage regulator to supply

the 100-mA current surge.

If operating from a single supply, use a 22-Ω resistor in series

with the VDD supply line and a 1-μF low ESR capacitor to filter

any power supply noise. The previous capacitor placement

considerations apply.

Figure TMD3782 – 41:

Typical Application Hardware Circuit

VBUS in the above figure refers to the I

2C bus voltage which is

either VDD or 1.8 V. Be sure to apply the specified I

2C bus voltage

shown in the Available Options table for the specific device

being used.

The I2C signals and the Interrupt are open-drain outputs and

require pull−up resistors. The pull-up resistor (RP) value is a

function of the I2C bus speed, the I2C bus voltage, and the

capacitive load. The ams EVM running at 400 kbps, uses 1.5-kΩ

resistors. A 10-kΩ pull-up resistor (RPI) can be used for the

interrupt line.

Application Information

TMD37827 Datasheet(PDF) 27 Page - ams AG