C11 datasheet(54/72 Pages) AMSOSRAM

54 / 72 page

AS3688

austriami crosyst ems

Datasheet, Confidential

www.austriamicrosystems.com (ptr,tje)

Revision 1.1.1 / 20060707

52 - 70

Table

20 – Function Testing for LEDs connected to the DCDC converter

Step

Action

Example Code

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. To

reduce the settling time of the DCDC converter to changes of step_up_vtuning, the external capacitors C10 and

C11 can be changed to C10=150pF and C11=1.5nF.

7.7

Analog-To-Digital Converter

The AS3688 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

21 – ADC Input Ranges, Compliances and Resolution

Channels (Pins)

Input Range

VLSB

Note

GPIO0, GPIO1, GPIO2, GPI, DCDC_FB

0V-2.5V

2.44mV

VLSB=2.5/1024

ADCTEMP_CODE

TBD

1 / ADCTC

junction temperature

RGB1,RGB2,RGB3,

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

VBAT2, CP_OUT

0V-5.5V

6.1mV

VLSB=2.5/1024 * 1/0.4;

internal resistor divider used

CURR1, CURR2

0V-1.0V

2.44mV

VLSB=2.5/1024

Table

22 – 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 used as

reference for ADC converter

Idd

Power Supply Current

500

µ A

During conversion only.

Idd

Power Down Current

100

TTOL

Temperature Sensor

Accuracy

+/-5

°C

@ 25 °C

ADCTOFFSET

ADC temperature

measurement offset value

375

Code

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