
ADT14
–6–
REV. 0
APPLICATIONS INFORMATION
Programming the ADT14
To program any of the four temperature trip points, simply set
the voltage at the setpoint pin equal to the voltage expected at
the VPTAT output at the desired trip temperature. The on-
board 2.5 V precision reference provides a temperature stable
output that is used to establish the setpoint voltages. Figure 14
illustrates the basic temperature setpoint configuration. This
parallel resistor ladder configuration uses six resistors to set the
four setpoint voltages.
I
L
I
L2
R4
I
L1
R1
R2
R5
R3
R6
V
REF
SET 4
SET 3
SET 2
SET 1
GND
ADT14
HYS
Figure 14. ADT14 Setpoint Programming
For SET4,
T4 = 100
°
C
V(SET4) = (T4 + 273.15)(5 mV/K)
For SET1,
T1 = 75
°
C
V(SET1) = (T1 + 273.15)(5 mV/K)
Choose I
L1
= I
L2
= 25
μ
A,
R1 = (V
REF
– V[SET4])/I
L1
R2 = (V[SET4] – V[SET1])/I
L1
R3 = V(SET1)/I
L1
For SET3,
T3 = 50
°
C
V(SET3) = (T3 + 273.15)(5 mV/K)
For SET2,
T2 = –10
°
C
V(SET2) = (T2 + 273.15)(5 mV/K)
Since I
L1
= I
L2
= 25
μ
A,
R4 = (V
REF
– V[SET3])/I
L2
R5 = (V[SET3] – V[SET2])/I
L2
R6 = V(SET2)/I
L2
For the example shown in Figure 14 and the related equations,
Setpoint 4 was chosen as highest temperature trip point, fol-
lowed in order by Setpoint 1, Setpoint 3 and Setpoint 2. The
user may choose to alter this order at will as all the setpoint
inputs and trip point outputs are identical in operation. The
minimum recommended parallel ladder resistance is 12.5 k
.
This maintains a V
REF
load current less than 200
μ
A. To avoid
errors, choose 50
μ
A < I
L
< 200
μ
A.
For those applications where setpoints do not need to be
changed, a single ladder of five resistors can be used. Figure 15
illustrates a single resistor ladder configuration.
50
μ
A < I
L
< 200
μ
A
R1 = (V
REF
– V[SET4])/I
L
R2 = (V[SET4] – V[SET1])/I
L
R3 = (V[SET1] – V[SET3])/I
L
R4 = (V[SET3] – V[SET2])/I
L
R5 = V(SET2)/I
L
I
L
R1
R2
R3
V
REF
R4
R5
SET4
SET1
SET3
SET2
50 A < I
< 200 A
T4 > T1 > T3 > T2
Figure 15. Single Resistor Ladder
Temperature Hysteresis
Temperature hysteresis is the number of degrees below the
original setpoint temperature that must be sensed by the
ADT14 before the setpoint comparator will be reset and the
open-collector output disabled. Figure 16 shows the hysteresis
profile. Hysteresis is programmed by the user by setting a speci-
fied voltage at the hysteresis pin (See Table I).
HYSTERESIS
HI
LO
T
SET2
T
SET3
T
SET1
T
SET4
TEMPERATURE
O
Figure 16. ADT14 Hysteresis Profile
Table I. Common Hysteresis Values and Voltages
Hysteresis
Connect Pin 11 to
0.65
°
C
1.5
°
C
5
°
C
+2.5 V Reference
Leave Open
Ground
The voltage on Pin 11 programs the internal hysteresis current,
which is mirrored and fed to a buffer controlled by an analog
switch. After a temperature setpoint has been exceeded and a
comparator tripped, the buffer is enabled, allowing hysteresis
current to flow. This current generates a hysteresis offset voltage