AS1163 datasheet(39/91 Pages) AMSOSRAM

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AS1163

Functional description

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6.6.1

LED temperature compensation

In color-accurate RGB applications, the host MCU synthesizes a color with the PWM settings

of the 3 LED drivers for each channel. In this case, each PWM triplet is already taking into

account the chip temperature.

Chip junction temperature is obtained by a status register request, as estimation of the LED

temperature, creating an accurate color despite the absolute LED temperature variations.

This feature implements small corrections to the programmed PWM values, proportionally to

the difference between the reference temperature and the actual temperature, in steps of 4

LSBs.

The temperature correction factor is sent by the host together with the reference temperature

using SETTCOEFFCHN telegram. Once the absolute delta between actual temperature and

reference temperature is larger than k*TEMP_STEP, k=1,2,3,… the correction factor is applied

to the PWM proportionally using the formula:

Equation 2:

��(��) = �� ( ��) [1 + �� (��)(�� − ��)]

Before every new PWM frame is started, the temperature delta is checked and in case

compensation is required this is calculated and applied one channel at a time.

Programmed temperature coefficient and reference temperature can be read by the

READTCOEFFCHN command.

The compensation happens only when the device is in active state.

The following conditions will automatically trigger a start of compensation calculation process:

1. Host changes any PWM values, current value, reference temperatures or correction

factors.

2. Actual temperature changes.

3. Device state goes from sleep/deep-sleep to active state

Within one compensation calculation, compensation of every driver is calculated once and in a

sequential manner R0, B0, G0, R1, B1, G1, R2, B2, G2. For each driver it takes 55 system

clock cycles to complete (2.86 µs). So, for one entire compensation, it takes nominally (55*9) +

1 clock cycles = 25.83 µs to complete.

To disable this function, host should set the correction factor all to zero.

All corrected PWM values are reset to 0 when the device is not in active state.

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