AS3689 datasheet(54/72 Pages) AMSOSRAM

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AS3689

austriami crosyst ems

Datasheet, Confidential

www.austriamicrosystems.com (mlg, ptr)

Revision 1.0.2 / 20070115

52 - 70

Table 21 – Function Testing for LEDs connected to the DCDC converter

Step

Action

Example Code

12.

Switch off the DCDC converter

Reg 00h <- 00h

13.

The voltage on the LED string can be calculated now

as follows (R4 = open):

VLEDSTRING = V(DCDC_FB) + I(step_up_vtuning) *

R3 – 0.5V (current sinks feedback voltage: VFB2).

V(DCDC_FB) = ADC Measurement from point 11

I(step_up_vtuing) = last setting used for point 10

e.g.: VLED = (1.602V + 12V – 0.5V) / 4 = 3.276V

14.

Compare the calculated value against the

specification limits of the tested LEDs

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

7.7

Analog-To-Digital Converter

The AS3689 has a built-in 10-bit successive approximation analog-to-digital converter (ADC). It is internally

supplied by V2_5, which is also the full-scale input range (0V defines the ADC zero-code). For input signal

exceeding V2_5 (typ. 2.5V) a resistor divider with a gain of 0.4 (Ratioprescaler) is used to scale the input of the

ADC converter. Consequently the resolution is:

Table 22 – ADC Input Ranges, Compliances and Resolution

Channels (Pins)

Input Range

VLSB

Note

GPIO, GPI, DCDC_FB

0V-2.5V

2.44mV

VLSB=2.5/1024

ADCTEMP_CODE

-30°C to 125°C

1 / ADCTC

junction temperature

RGB1,RGB2,RGB3,

CURR{30, 31, 32, 33, 41, 42, 43, 51,52}

VBAT2, CP_OUT

0V-5.5V

6.1mV

VLSB=2.5/1024 * 1/0.4;

internal resistor divider used

CURR1, CURR2, CURR6

0V-1.0V

2.44mV

VLSB=2.5/1024

Table 23 – ADC Parameters

Symbol

Parameter

Min

Typ

Max

Unit

Note

Resolution

Bit

Vin

Input Voltage Range

VSS

Vsupply

Vsupply = V2_5

DNL

Differential Non-Linearity

± 0.25

LSB

INL

Integral Non-Linearity

± 0.5

LSB

Vos

Input Offset Voltage

± 0.25

LSB

Rin

Input Impedance

100

MΩ

Cin

Input Capacitance

Vsupply (V2_5)

Power Supply Range

2.5

± 2%, internally trimmed.

Idd

Power Supply Current

500

µ A

During conversion only.

Idd

Power Down Current

100

TTOL

Temperature Sensor

Accuracy

-10

+10

°C

@ 25 °C

ADCTOFFSET

ADC temperature

measurement offset value

375

Code

ADCTC

Code temperature

coefficient

1.2939

Code/°C

Temperature coefficient of ADC

code for temperature

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