EPC635 datasheet(20/97 Pages) EPC

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The LED pin is the internal open-drain IR LED/LD driver output. When the driver is active (on), the IR LED/LD on-current flows through the

power resistor R3 into the LED pin, through the driver and comes out of the chip on the VSSLED ground pin.

■ The LED pin toggles up to 20MHz or according to the MODCLK clock with a current maximum of 500mA limited by the resistor R3.

■ The number of IR LEDs depends on the level of the LED supply voltage and the turned-on forward voltage drop of the IR LEDs.

■ This signal creates a lot of ground noise. Therefore, VSSLED pin is decoupled from the other analog grounds internally. It must be shor-

ted with the other analog ground pins with a low-ohmic connection as short as possible on the PCB. In this way, there will be minimal

voltage differences in the ground planes of the board.

■ The LED supply line must be isolated properly from any analog supply on the PCB to minimize noise coupling from the LED drivers.

The LEDFB pin is the amplifier input for the LED feedback signal. The easiest way is to pick it from a voltage divider R1 and R2 following

the IR LEDs on the PCB.

Cycle to cycle jitter

from LED pin falling (active) edge

to LEDFB pin rising (active) edge

LED

LEDFB

maximum allowed input voltage LEDFB pin = 8.5V

maximum allowed output voltage LED pin = 6.5V

LED external loop delay

jitter < 300 ps

Figure 15: LED and LEDFB pin signal restrictions

The LED2 pin is the alternative push-pull driver providing symmetric rise/fall times to drive external LED driver.

■ It works from the +2.5/+3.3 VDDIO supply (VSSIO GND domain) and swings in the same voltage range like the TCMI pins.

■ LED2 = LOW (approx. 0v) corresponds to LED = OFF (max. output voltage).

■ Because non of the TCMI pads toggle during integration time, LED2 pin is the only toggling during integration time and it is not affected

from switching noise of others.

■ It can toggle up to 20MHz and deliver up to +/-50mA peak.

■ LED and LED2 pins must not be used at the same time for driving the external illumination. They exhibit different phase delays and this

can result wrong distance measurements.

LEDFB pin is the feedback amplifier input.

■ Refer to Figure 15 for input signal integrity and restrictions at the LEDFB pin.

TCK, TMS, TDI, TDO are standard JTAG controller pins (Additional information upon request)

It is recommended having “not connected pins” (NC) on test pads available. It helps e.g. to check after assembly for correct orientation of

the chip or for short-cuts.

To guarantee the proper function of the chip, the remaining, not here listed pins have to be connected according Figure 14.

Characteristics subject to change without notice

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Datasheet_epc635-V1.02

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