AS3677 datasheet(51/68 Pages) AMSCO

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AS3677

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

8.6.2

Function Testing example for LEDs connected to the DCDC

Use following procedure as an example:

Note:

With the above described procedures electrically open and shorted LEDs can be automatically detected

8.7

Analog-to-Digital Converter

The AS3677 has a built-in 10-bit successive approximation analog-to-digital converter (ADC). It is internally supplied

which is also the full-scale input range (0V defines the ADC zero-code). For input signals exceeding 2.5V a resistor

divider with a gain of 0.5 (Ratioprescaler) is used to scale the input of the ADC converter. Consequently the resolution

is:

Measure with the ADC the voltage on the switched

on current sink

Reg 26h

≤ 85h (adc_select=RGB1,start ADC)

Fetch the ADC result from Reg 27h and 28h

Switch off the current sink for the LED to be tested

Reg 02h

≤ 00h (rgb1_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 charge pump automatic mode

Reg 00h

≤ 00h (cp_on = 0)

Reg 23h

≤ 00h

Table 86. Function Testing procedure for LEDs connected to the DCDC

Step

Action

Example Code

Switch on one current sink (only one!) for the LED

string to be tested (CURR1,2 or 6) - this example

uses CURR1

e.g. Test LEDs on CURR1:

Reg 01h

≤ 01h (curr1_mode=on)

Reg 09h

≤ 3ch (curr1_current = 9mA)

Select the feedback path for the LED string to be

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

CURR1) and disable automatic feedback

Reg 21h

≤ 02h (step_up_fb=CURR1)

Reg 22h <- 04h (step_up_fb_auto=off)

Set step_up_vmax to fit the external components

used (e.g. max 16V)

Reg 21h <- 00h (for 16V maximum output voltage)

Switch on the DCDC converter

Reg 00h

≤ 08h

Wait 2ms (dcdc startup time and some margin)

Measure the voltage on CURR1

Reg 26h

≤ 98h (adc_select=CURR1, start ADC;

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

If the voltage on CURR1 is below 1.0V but above

0.1V, this LED string is working fine (typical value

will be at 0.5V)

For a proper working LED result must be below

<199h (1.0V) and above >29h (0.1V)

Switch off current sink CURR1

Reg 01h

≤ 00h (curr1_mode=off)

Repeat whole procedure for each used LED string

(replace CURR1 with CURR2 or CURR6)

Table 87. ADC Input Ranges, Compliances and Resolution

Channels (Pins)

Input Range

VLSB

Note

ALS/GPIO1, GPIO2, GPIO3 and

VANA, DLS1, DLS2

0V-2.5V

2.44mV

VLSB=2.5/1024

ADCTEMP_CODE

-30°C to 125°C

1 / ADCTC

junction temperature

Table 85. Function Testing for LEDs connected to the Charge Pump

Step

Action

Example Code

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