Cirrus Logic CS1613 - Manual (Page 13)

CS1610/11/12/13
DS929F6 13
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 rest of the
system will not be initialized until the external temperature is
below 110
C.
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 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).
Current I
LED
starts reducing when resistor R
NTC
is
approximately 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). LED current I
LED
is scaled
until the NTC value reaches 2.5k  (125°C).
The CS1610/11/12/13 uses the calculated value of the
second low-pass filter to scale output LED current I
LED
, as
shown in Figure 15.
If the measured temperature exceeds 125°C, 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.
Temperature ( °C)
C
u
rr
e
n
t
(I
LE
D
, N
o
m
.)
125 95
50%
100%
0
25
Figure 15. LED Current vs. eOTP Temperature