Datasheet
R
pull-up
= V
DD (Max)
± V
OL
i
T
i
T
= i
L
+ i
sink
OVERTEMP
V
DD
R
Pull-Up
V
OUT
i
L
i
T
i
sink
Digital Input
(-12.8 mV/°C)
x
V =
(T-20°C) + 2396 mV
(-12.8 mV/°C)
x
V - 2396 mV =
(T - 20°C)
V
2
- V
1
T
2
- T
1
u
¹
·
¹
·
V - V
1
= (T - T
1
)
SM72480
SNIS156C –NOVEMBER 2010–REVISED APRIL 2013
www.ti.com
First-Order Approximation (Linear) over Small Temperature Range
For a linear approximation, a line can easily be calculated over the desired temperature range from the
Conversion Table using the two-point equation:
(3)
Where V is in mV, T is in °C, T
1
and V
1
are the coordinates of the lowest temperature, T
2
and V
2
are the
coordinates of the highest temperature.
(4)
(5)
Using this method of linear approximation, the transfer function can be approximated for one or more
temperature ranges of interest.
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 simultaneously 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 digital 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.
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
DD
. The following section shows how to determine the pull-up resistor value.
Figure 9. Determining the Pull-up Resistor Value
The Pull-up resistor value is calculated at the condition of maximum total current, i
T
, through the resistor. The
total current is:
where
• i
T
is the maximum total current through the Pull-up Resistor at V
OL
.
• i
L
is the load current, which is very low for typical digital inputs.
• V
OUT
is the Voltage at the OVERTEMP pin. Use V
OL
for calculating the Pull-up resistor.
• V
DD(Max)
is the maximum power supply voltage to be used in the customer's system. (6)
The pull-up resistor maximum value can be found by using the following formula:
(7)
EXAMPLE CALCULATION
Suppose we have, for our example, a V
DD
of 3.3 V ± 0.3V, a CMOS digital input as a load, a V
OL
of 0.2 V.
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