SM72480

Manufacturer Part NumberSM72480
ManufacturerTexas Instruments
SM72480 datasheet
 


Specifications of SM72480

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2.0 OVERTEMP and OVERTEMP
Digital Outputs
The OVERTEMP Active High, Push-Pull Output and the
OVERTEMP Active Low, Open-Drain Output both assert at
the same time whenever the Die Temperature reaches the
factory preset Temperature Trip Point. They also assert si-
multaneously whenever the TRIP TEST pin is set high. Both
outputs de-assert when the die temperature goes below the
Temperature Trip Point - Hysteresis. These two types of dig-
ital outputs enable the user the flexibility to choose the type
of output that is most suitable for his design.
Either the OVERTEMP or the OVERTEMP Digital Output pins
can be left open if not used.
2.1 OVERTEMP OPEN-DRAIN DIGITAL OUTPUT
The OVERTEMP Active Low, Open-Drain Digital Output, if
used, requires a pull-up resistor between this pin and V
The following section shows how to determine the pull-up re-
sistor value.
Determining the Pull-up Resistor Value
The Pull-up resistor value is calculated at the condition of
maximum total current, i
, through the resistor. The total cur-
T
rent is:
where,
i
i
is the maximum total current through the Pull-up
T
T
Resistor at V
.
OL
i
i
is the load current, which is very low for typical
L
L
digital inputs.
V
V
is the Voltage at the OVERTEMP pin. Use
OUT
OUT
V
for calculating the Pull-up resistor.
OL
V
V
is the maximum power supply voltage to be
DD(Max)
DD(Max)
used in the customer's system.
The pull-up resistor maximum value can be found by using
the following formula:
EXAMPLE CALCULATION
Suppose we have, for our example, a V
CMOS digital input as a load, a V
OL
www.national.com
(1) We see that for V
OVERTEMP shows a maximim i
(2) Let i
35 µA as the current limit then i
35 µA
(3) We notice that V
calculate the pull-up resistor as
R
Pull-up
(4) Based on this calculated value, we select the closest re-
sistor value in the tolerance family we are using.
In our example, if we are using 5% resistor values, then the
next closest value is 100 kΩ.
2.2 NOISE IMMUNITY
The SM72480 is virtually immune from false triggers on the
OVERTEMP and OVERTEMP digital outputs due to noise on
the power supply. Test have been conducted showing that,
.
with the die temperature within 0.5°C of the temperature trip
DD
point, and the severe test of a 3 Vpp square wave "noise"
signal injected on the V
5V, there were no false triggers.
3.0 TRIP TEST Digital Input
The TRIP TEST pin simply provides a means to test the
OVERTEMP and OVERTEMP digital outputs electronically
by causing them to assert, at any operating temperature, as
a result of forcing the TRIP TEST pin high.
When the TRIP TEST pin is pulled high the V
at the V
If not used, the TRIP TEST pin may either be left open or
grounded.
4.0 V
Sensor Output
The V
TEMP
30142052
source significant current. This is beneficial when, for exam-
ple, driving dynamic loads like an input stage on an analog-
to-digital converter (ADC). In these applications the source
current is required to quickly charge the input capacitor of the
ADC. See the Applications Circuits section for more discus-
sion of this topic. The SM72480 is ideal for this and other
applications which require strong source or sink current.
4.1 NOISE CONSIDERATIONS
The SM72480's supply-noise rejection (the ratio of the AC
signal on V
ing bench tests. It's typical attenuation is shown in the Typical
Performance Characteristics section. A load capacitor on the
output can help to filter noise.
For operation in very noisy environments, some bypass ca-
pacitance should be present on the supply within approxi-
mately 2 inches of the SM72480.
4.2 CAPACITIVE LOADS
The V
TEMP
tremely noisy environment, or when driving a switched sam-
pling input on an ADC, it may be necessary to add some
filtering to minimize noise coupling. Without any precautions,
the V
TEMP
1100 pF as shown in
than 1100 pF, a series resistor is required on the output, as
of 3.3 V ± 0.3V, a
shown in
DD
of 0.2 V.
12
of 0.2 V the electrical specification for
OL
of 385 µA.
sink
= 1 µA, then i
is about 386 µA max. If we select
L
T
for the calculation becomes
T
is 3.3V + 0.3V = 3.6V and then
DD(Max)
= (3.6 − 0.2)/35 µA = 97k
line, over the V
range of 2V to
DD
DD
TEMP
voltage.
TRIP
Analog Temperature
TEMP
push-pull output provides the ability to sink and
to the AC signal on V
) was measured dur-
TEMP
DD
Output handles capacitive loading well. In an ex-
can drive a capacitive load less than or equal to
Figure
1. For capacitive loads greater
Figure
2, to maintain stable conditions.
pin will be