CS1610 Datasheet, PDF (13/17 Pages) Cirrus Logic – TRIAC Dimmable LED Driver IC

CS1610/11/12/13
The ADC output code is filtered to suppress noise and
compared against a reference code that corresponds to
125/130°C. If the temperature exceeds this threshold, the
chip enters an external overtemperature state and shuts
down. This is not a latched protection state, and the ADC
keeps tracking the temperature in this state in order to clear
the fault state once the temperature drops below 110°C.
When exiting reset, the chip enters startup and the ADC
quickly (<5ms) tracks the external temperature to check if it is
below the 110°C reference code before the boost and second
stages are powered up. If this check fails, the chip will wait
until this condition becomes true before initializing the rest of
the system.
For external overtemperature protection, a second low-pass
filter with a time constant of two minutes filters the ADC output
and uses it to scale down the internal dim level of the system
(and hence the LED current, I_LED) if the temperature exceeds
95 °C (see Figure 15). The large time constant for this filter
ensures that the dim scaling does not happen spontaneously
and is not noticeable (suppress spurious glitches). The I_LED
starts reducing when R_NTC ~ 6.3k (assuming a 14k1%
tolerance, series resistor), which corresponds to a
temperature of 95°C for a 100k NTC (100k at 25°C). The
I_LED current is scaled until the NTC value reaches 2.5k
(125°C). The CS1610/11/12/13 uses this calculated value to
scale the output LED current, I_LED, as shown in Figure 15.
100%
50%
0
25
95
125
Temperature (°C)
Figure 15. LED Current vs. eOTP Temperature
Beyond this temperature, the IC shuts down using the
mechanism discussed above. If the external overtemperature
protection feature is not required, connect the eOTP pin to
GND using a 50k-to-500k resistor to disable the eOTP
feature.
DS929F5
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