TMP01GBC AD [Analog Devices], TMP01GBC Datasheet - Page 14

• Manufacturer Part Number: TMP01GBC
• Description: Low Power, Programmable Temperature Controller
• Manufacturer: AD [Analog Devices]

TMP01
Isolation Amplifier
In many industrial applications the sensor is located in an envi-
ronment that needs to be electrically isolated from the central
processing area. Figure 21 shows a simple circuit that uses an
8-pin optoisolator (IL300XC) that can operate across a 5,000 V
barrier. IC1 (an OP290 single-supply amplifier) is used to drive
the LED connected between Pins 1 to 2. The feedback actually
comes from the photodiode connected from Pins 3 to 4. The
OP290 drives the LED such that there is enough current gener-
ated in the photodiode to exactly equal the current derived from
the VPTAT voltage across the 470 k resistor. On the receiving
end, an OP90 converts the current from the second photodiode
to a voltage through its feedback resistor R2. Note that the other
amplifier in the dual OP290 is used to buffer the 2.5 V reference
voltage of the TMP01 for an accurate, low drift LED bias level
without affecting the programmed hysteresis current. A REF43
(a precision 2.5 V reference) provides an accurate bias level at
the receiving end.
To understand this circuit, it helps to examine the overall equa-
tion for the output voltage. First, the current (I1) in the photo-
diode is set by:
Note that the IL300XC has a gain of 0.73 (typical) with a min
and max of 0.693 and 0.769 respectively. Since this is less than
1.0, R2 must be larger than R1 to achieve overall unity gain. To
show this the full equation is:
A trim is included for R2 to correct for the initial gain accuracy
of the IL300XC. To perform this trim, simply adjust for an out-
put voltage equal to VPTAT at any particular temperature. For
V OUT
2. 5 V – I 2 R 2
R2
R1
R3
1
2
3
4
VREF
GENERATOR
HYSTERESIS
I
2. 5 V – 0. 7
1
TEMPERATURE
COMPARATOR
REFERENCE
SENSOR &
VOLTAGE
WINDOW
2.5 V – VPTAT
470 k
OP290
2. 5 V – VPTAT
TMP01
470 k
VPTAT
8
7
6
5
V+
470k
R1
644 k
Figure 21. Isolation Amplifier
3
2
VPTAT
OP290
V+
7
4
680pF
6
–14–
100
example, at room temperature, VPTAT = 1.49 V, so adjust R2
until V
operate from a single supply, and contribute no significant error
due to drift.
In order to avoid the accuracy trim, and to reduce board space,
complete isolation amplifiers are available, such as the high
accuracy AD202.
Out-of-Range Warning
By connecting the two open collector outputs of the TMP01
together into a “wired-OR” configuration, a temperature “out-
of-range” warning signal is generated. This can be useful in sen-
sitive equipment calibrated to work over a limited temperature
range. R1, R2, and R3 in Figure 22 are chosen to give a tem-
perature range of 10 C around room temperature (25 C). Thus,
if the temperature in the equipment falls below +15 C or rises
above +35 C, the Undertemp Output or Overtemp Output re-
spectively will go low and turn the LED on. The LED may be
replaced with a simple pull-up resistor to give a logic output for
controlling the instrument, or any of the switching devices dis-
cussed above can be used.
IN4148
47.5k
4.99k
71.5k
OUT
R1
R2
R3
1
2
3
4
= 1.49 V as well. Both the REF43 and the OP90
ISOLATION
IL300XC
Figure 22. Out-of-Range Warning
BARRIER
1
2
3
4
I
1
VREF
I
2
HYSTERESIS
GENERATOR
TEMPERATURE
COMPARATOR
REFERENCE
5
6
SENSOR &
VOLTAGE
WINDOW
2.5V
604k
6
3
2
TMP01
OP90
680pF
REF43
VPTAT
100k
V+
7
4
2
4
6
8
7
6
5
V+
1.16V TO 1.7V
V+
VPTAT
LED
200
REV. C