Cs1680 – Cirrus Logic CS1680 User Manual
Page 13
CS1680
DS1055F1
13
When exiting reset, the chip enters startup and the ADC
quickly (<15ms) tracks the external temperature to check
if it is below 120°C reference code before the controller is
powered up. If this check fails, the chip will wait until this
condition becomes true before initializing the rest of the
system; that is, until the resistance (R
S
+R
NTC
) rises above
17.02k
.
For example, a 14k
(±1% tolerance) series resistor is
required to allow measurements of up to 130°C to be
within the eOTP tracking range when a 100k
NTC with a
Beta of 4275. If the temperature exceeds 95°C,
thermistor R
NTC
is approximately 6.3k
and series
resistor R
S
is 14k
, so the eOTP pin has a total resistance
of 20.3k
. The eOTP pin initiates protective dimming
action by reducing the power dissipation. At 125°C, the
thermistor R
NTC
has 2.6k
plus a series resistor R
S
equal
to 14k
present a resistance of 16.6k at the eOTP pin
reaching the point where a thermal shutdown fault
intervenes. The CS1680 fault state is not cleared until the
power to the IC is recycled (see Figure 15).
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