Cirrus Logic CS1613A - Manual (Page 14)

CS1610A/11A
CS1612A/13A
14 DS976F1
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 18). The large time constant for this filter
ensures that the dim scaling does not happen spontaneously
and is not noticeable (suppress spurious glitches). LED
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 thermistor value reaches 2.5k  (125°C). The
CS1610A/11A/12A/13A uses this calculated value to scale
output LED current I
LED
, as shown in Figure 18.
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.
Temperature ( °C)
C
u
rr
e
n
t
(I
LE
D
, N
o
m
.)
125 95
50%
100%
0
25
Figure 18. LED Current vs. eOTP Temperature