LTC2995
APPLICATIONS INFORMATION
Output Noise Filtering
pulledlowifthevoltageV
fallsduringfiveconsecutive
PTAT
conversions below the undertemperature threshold VT1.
Once pulled low, TO1 is released high again if V rises
The V
output typically exhibits 0.6mV RMS (0.25°C
PTAT
PTAT
RMS) noise. For applications which require lower noise
digital or analog averaging can be applied to the output.
Choose the averaging time according to:
above VT1 plus an additional hysteresis of about 20mV.
Accordingly, T02 is pulled low if the voltage V rises
PTAT
abovetheovertemperaturethresholdVT2and–oncepulled
2
low– TO2 is released high if V falls below VT2 minus
⎛
⎜
⎝
⎞
PTAT
[
]
°
0.01 C Hz
anadditionalhysteresisofabout20mV.LeavingPSuncon-
nected configures both VT1 and VT2 as overtemperature
thresholds and connecting PS to GND configures them
both as undertemperature thresholds. If the internal and
external sensors are monitored alternately by leaving DS
unconnected, VT1 becomes a dedicated threshold for the
internal sensor and VT2 becomes a dedicated threshold
for the external sensor.
⎟
⎠
tAVG
=
T
NOISE
where t
is the averaging time and T
the desired
NOISE
AVG
temperature noise in °C RMS. For example, if the desired
noiseperformanceis0.015°CRMS,settheaveragingtime
to one second. See Typical Performance Characteristics.
Temperature Monitoring
Temperature Monitor Design Example
The LTC2995 continuously compares the voltage at V
PTAT
The LTC2995 can be configured to give an early warning
if the temperature of the internal sensor rises above 60°C
and an alarm if the temperature passes 90°C. Tie the DS
to the voltages at the pins VT1 and VT2 to detect either an
overtemperature(OT)orundertemperature(UT)condition.
The VT1 comparator output drives the open-drain logic
output pin TO1 and the VT2 comparator output drives the
open-drain logic output pin TO2. The polarity of these
comparisons is configured via the three-state polarity
select pin (PS) (Table 3).
pin to V to select the internal sensor and leave the pin
CC
PS unconnected to configure both input voltages VT1 and
VT2 as overtemperature thresholds. The voltages at VT1
and VT2 are set to:
mV
K
Table 3. Temperature Polarity Selection
VT1 =(60K + 273.15K) • 4
= 1.332V
= 1.452V
PS PꢁN
FUN°TꢁON
°ONDꢁTꢁON OUTPUT
VT1 Undertemperature
Threshold
mV
K
V
PTAT
V
PTAT
V
PTAT
V
PTAT
V
PTAT
V
PTAT
< VT1 TO1 Pulled Low
> VT2 TO2 Pulled Low
> VT1 TO1 Pulled Low
> VT2 TO2 Pulled Low
< VT1 TO1 Pulled Low
< VT2 TO2 Pulled Low
VT2 =(90K + 273.15K) • 4
V
CC
VT2 Overtemperature
Threshold
WhenV
reachesthethresholdvoltageonpinVT1,TO1
PTAT
VT1 Overtemperature
Threshold
is pulled low indicating an overtemperature early warning.
If the temperature reaches 90°C TO2 is also pulled low,
indicating an overtemperature alarm.
Open
GND
VT2 Overtemperature
Threshold
VT1 Undertemperature
Threshold
Once the temperature drops below each threshold, the
corresponding TO pins will return high after a time-out-
VT2 Undertemperature
Threshold
period (t
) set by the capacitor connected to TMR.
UOTO
If pin PS is connected to V , the voltage on VT1 becomes
CC
an undertemperature threshold and the voltage on VT2
an overtemperature threshold. In this configurationTO1 is
2995f
12
Linear Systems [ Linear Systems ]
