ADT14GP AD [Analog Devices], ADT14GP Datasheet - Page 14

• Manufacturer Part Number: ADT14GP
• Description: Quad Setpoint, Programmable Temperature Monitor and Controller
• Manufacturer: AD [Analog Devices]

ADT14
Intelligent Temperature Control System—Interfacing the
8051 C with the ADT14
Connecting the 8051, or any modern microcontroller, with the
ADT14 yields a powerful temperature control tool. For ex-
ample, by using digitally controlled resistors (AD8402/3), a user
may automatically set the temperature trip points via computer
or touch pad. The ADT14 outputs are fed back to the controller
allowing it to sense whether or not a setpoint has been exceeded.
The higher temperature trip-point data can then be used to turn
on a fan to either a high or low setting. In addition, the lower
temperature trip-point data may be used to turn on a heater to
either a high or low setting.
The AD8403 is shown in a single ladder resistor configuration
with an additional fix resistor to set the voltages of all four
setpoints. The microcontroller program that runs the AD8403
can also be set to ensure that no out-of-bound conditions occur.
Finally, the AD8403 also has shutdown pin which, when acti-
vated, will lower power consumption to 5 A max (0.01 A
typical), while still retaining memory of the potentiometer set-
tings.
Power-Down in Battery Powered Applications
Battery powered applications require low power consumption
components. The ADT14 is just such a device. The low supply
current (< 600 A) of the ADT14 makes it possible to power
the device from any suitable logic output pin. Figure 29 is a
schematic of an 'HC04 CMOS inverter driving the ADT14. When
the SLEEP pin is high, the ADT14 is powered down. Figure 5
shows a typical start-up response of an ADT14. Most tempera-
ture measurements vary slowly over time, which allows designs
INPUTS
0.1 F
USER
0.1 F
P0.0 TO
P0.7
P1.0/INT2
OUT
CONT
80CL51 C
TLC555
GND
+5V
V
CC
TRIG
THR
DIS
RS
P3.2
P3.1
P3.0
P3.3
P2.0
P2.1
P2.2
P2.3
P2.4
TO 2ND
AD8403
Figure 28. Typical Microcontroller Setup Configuration
CS
CLK
SDI
SHDN
AD8403
GND
V
DD
–14–
that consume very little power over very long periods of time by
using a duty-cycling technique. The basic idea of the duty-
cycling technique is to simply measure the temperature at se-
lected time intervals and leave the device powered down the rest
of the time. Instead of a CMOS inverter, any other logic pin
with sufficient drive capability (such as the output of a micro-
processor) can be used to power on and off the ADT14.
Combining Trip Point Outputs to Yield 25%, 50%, 75%, and
100% Power Outputs
It is often desirable to power a device at varying levels based
upon ambient temperature. For example, suppose a liquid is
below a desired temperature, the lowest trip point temperature.
In this case, full power should be delivered to the heating ele-
ment, causing the temperature to rise as rapidly as possible.
When the lowest trip-point is finally crossed, a reduction in
power should occur, slowing the rate of increase in the heating
process. This process continues until all trip points are crossed
and the current to the heating element is reduced to zero.
Figure 29. Using a CMOS Inverter to Power Down the
ADT14
10 F
+5V
SLEEP
2.5V
SET1
SET2
SET3
SET4
REF
ADT14
'HC04
TRIP1
TRIP2
TRIP3
TRIP4
GND
HYS
V
DD
NC
ADT14
V+
0.1 F
NC = NO CONNECT
+5V
REV. 0