LTC2995
APPLICATIONS INFORMATION
Temperature Thresholds
The following design procedure can be used to size the
resistive divider.
The threshold voltages at VT1 and VT2 can be set with
the 1.8V reference voltage (V ) and a resistive divider
1. Calculate Threshold Voltages:
REF
as shown in Figure 5.
mV
K
η
ACT
1.004
VT1 = T1• 4
•
η
mV
K
V
REF
= 1.8V
V
ACT
PTAT
SLOPE =
tꢀꢁꢀ
ꢂꢃꢄꢄꢁ
mV
K
η
ACT
1.004
VT2 = T2 • 4
•
1.8V
VT2
R
TC
R
where η denotes the actual ideality factor if an external
TB
ACT
VT1
sensor is used and T1 and T2 are the desired threshold
O.8V
temperatures in degrees Kelvin.
R
TA
2. Choose R to obtain the desired VT1 threshold for
TA
T
a desired current through the resistive divider
2995 F05
O
200k
T
1
T
ꢁꢅꢄL
2
(I ):
REF
Figure 5. Temperature Thresholds
VT1
R
=
TA
I
REF
3. Choose R to obtain the desired VT2 threshold:
TB
VT2 – VT1
R
=
TB
I
REF
3.3V
+
D
DS
V
PS
LTC2995
CC
V
CC
V
CC
400k
TO2
+
1.2V
1.8V
V
REF
–
OT ALARM
200k
400k
R
TC
V
CC
VT2
VT1
–
+
400k
TO1
TO1/TO2
PULSE
GENERATOR
UVLO
R
R
TB
OT WARNING
–
+
V
PTAT
T/V
TA
–
D
GND
2995 F06
Figure 6. Monitoring ꢁnternal Temperature with Two Overtemperature Thresholds
2995f
13
Linear Systems [ Linear Systems ]
