C11 datasheet(53/72 Pages) AMSOSRAM

53 / 72 page

AS3688

austriami crosyst ems

Datasheet, Confidential

www.austriamicrosystems.com (ptr,tje)

Revision 1.1.1 / 20060707

51 - 70

Table

19 – Function Testing for LEDs connected to the Charge Pump

Step

Action

Example Code

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 = curr3x_other)

Measure with the ADC the voltage on CP_OUT

Reg 26h <- 95h (adc_select=CP_OUT,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

Do the same procedure for the next LED starting from

point 2

Jump to 2. If not all the LEDs have been tested

Switch off the charge pump

set chargepump automatic mode

Reg 00h <- 00h (cp _on = 0)

Reg 23h <- 00h

Note: For CURR41,42,43 first set the charge pump into 1:1 mode and test if the LED is shorted. Then use the

above described procedure.

7.6.2 Function Testing for LEDs connected to the Step Up DCDC Converter

For LEDs connected to the DCDC converter (usually current sinks CURR1and CURR2) use the following

procedure:

Table

20 – Function Testing for LEDs connected to the DCDC converter

Step

Action

Example Code

Switch on the current sink for the LED string to be

tested (CURR1 or CURR2)

e.g. Test LEDs on CURR1:

Reg 01h <- 01h (curr1_mode=on)

Reg 09h <- 3ch (curr1 = 9mA)

Select the feedback path for the LED string to be

tested (e.g. step_up_fb = 01 for LED string on

CURR1)

Reg 21h <- 02h (feedback=curr1)

Set the current for step_up_vtuning exactly above the

maximum forward voltage of the tested LED string +

0.6V (for the current sink) + 0.25V; add 6% margin

(accuracy of step_up_vtuning); this sets the maximum

output voltage limit for the DCDC converter

e.g. 4 LEDs with UfMAX = 4.1V gives 17.25V +6%

= 18.29V; if R3=1MΩ and R4 = open, then select

step_up_vtuning = 18 (Reg 21h <- 92h; results in

19.25V overvoltage protection voltage – see table

in DCDC section)

Set stepup_prot = 1

Reg 22h <- 04h

Switch on the DCDC converter

Reg 00h <- 08h

Wait 1ms (DCDC startup time)

Measure the voltage on DCDC_FB (ADC)

Reg 26h <- 96h (adc_select=DCDC_FB, start

ADC; Fetch the ADC result from Reg 27h and 28h)

If the voltage on DCDC_FB is above 1.0V, the tested

LED string is broken – then skip the following steps

(Code >199h)

Switch off the overvoltage protection (stepup_prot = 0) Reg 22h <- 00h

10.

Reduce step_up_vtuning step by step until the

measured voltage on DCDC_FB (ADC) is above 1.0V.

e.g.: Reg 21h <- 62h (step_up_vtuning=12): ADC

result=1,602V

11.

Measure voltage on DCDC_FB

e.g. DCDC_FB=1.602V

12.

Switch off the DCDC converter

Reg 00h <- 00h

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