TMG39921 datasheet(83/96 Pages) OSRAM

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[v1-06] 2018-Feb-27

TMG3992 − Application Information

Power Supply Considerations

Systems using Proximity detection are capable of driving the

integrated LED with as much as 300mA of pulsed current;

however typical systems require much lower settings of 100mA

or less. As a result of the rapidly switching current on LDR pin,

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.

Systems where battery voltage does not exceed the maximum

specified LDR pin voltage (including battery recharge

conditions), the LEDA may be directly connected to the battery.

This is beneficial because noise generated by LED pulsing is not

couple into the supply of the optical device. Another advantage

for this configuration, depending on system design, may be a

reduction or removal of additional bulk capacitance connected

to LEDA.

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 1μF low-ESR decoupling capacitor as close as possible

to the VDD pin and another at the LEDA pin, along with a bulk

storage capacitor, 4.7μF or larger, (as needed) somewhere along

the trace to supply surge currents when the LED is pulsed.

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

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

any power supply noise. The previous capacitor placement

recommendations apply.

Figure 88:

Typical Application Hardware Circuit

Application Information

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