AS3676 datasheet(64/92 Pages) AMSCO

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AS3676

Datasheet - D e ta i l e d D e s c r i p t i o n

8.6

LED Test

Figure 26. LED Function Testing

The AS3676 supports the verification of the functionality of all the connected LEDs (open and shorted LEDs can be

detected). This feature is especially useful in production test to verify the correct assembly of the LEDs, all its connec-

tors and cables. It can also be used in the field to verify if any of the LEDs is damaged. A damaged LED can then be

disabled (to avoid unnecessary currents).

The current sources, charge pump, dcdc converter and the internal ADC are used to verify the forward voltage of the

LEDs. If this forward voltage is within the specified limits of the LEDs, the external circuitry is assumed to operate.

8.6.1

Function Testing for single LEDs connected to the Charge Pump

For any current source connected to the charge pump (CURR30-33) where only one LED is connected between the

charge pump and the current sink (see Figure 1) use:

Table 102. Function Testing for LEDs connected to the Charge Pump

Step

Action

Example Code

Switch on the charge pump and set it into manual

1:2 mode (to avoid automatic mode switching

during measurements)

Reg 23h

 14h (cp_mode = 1:2, manual)

Reg 00h

 04h (cp_on = 1)

Switch on the current sink for the LED to be tested

e.g. for register CURR31set to 9mA use

Reg 10h

 0Fh (curr3x_other = 9mA)

Reg 03h

 0ch (curr31_mode = curr31_other)

Measure with the ADC the voltage on CPOUT

Reg 26h

 95h (adc_select=CPOUT,start ADC)

Fetch the ADC result from Reg 27h and 28h

Measure with the ADC the voltage on the switched

on current sink

Reg 26h

 8bh (adc_select=CURR31,start ADC)

Fetch the ADC result from Reg 27h and 28h

Switch off the current sink for the LED to be tested

Reg 03h

 00h (curr31_mode = off)

Compare the difference between the ADC

measurements (which is the actual voltage across

the tested LED) against the specification limits of

the tested LED

Calculation performed in baseband uProcessor

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