8.2.2 TMP390 With 10°C Hysteresis

Figure 8-3 shows an example circuit for overtemperature and undertemperature protection using the TMP390. In

this example, the trip points are set at –25°C and +90°C with 10°C hysteresis.

TMP390

VDD

SETA

SETB

OUTA

OUTB

GND

Microprocessor

VCC

GND

78.7 kŸ

215 kŸ

10 kŸ

10 kŸ

0.1 µF

3.3 V

VDD = 3.0 V

Channel A Trip Temp = +90°C

and Hysteresis = 10°C

Channel B Trip Temp = ±25°C

and Hysteresis = 10°C

Figure 8-3. TMP390 Example Circuit at +90°C and –25°C Thresholds With 10°C Hysteresis

8.2.2.1 Design Requirements

In this example, VDD can be ≥ 3 V. The output pins may be tied to a switch to control a fan or other analog

circuitry. Figure 8-3 uses 10-kΩ pullup resistors at the OUTA and OUTB outputs. Place a 0.1-µF bypass

capacitor close to the TMP390 device to reduce noise coupled from the power supply. If needed, the output of

multiple parts can be connected together.

8.2.2.2 Detailed Design Procedure

SETA sets the +90°C threshold using 78.7 kΩ. SETB sets the –25°C trip point and 10°C hysteresis using 215

kΩ. These values were determined using Table 7-1 and Table 7-2. These resistors should have maximum of

1% tolerance and 100 ppm/°C or less over the desired temperature range. A summary of the resistor settings

used in this example is shown in Table 8-1. See Table 7-1 and Table 7-2 for additional trip points and hysteresis

configurations.

The switching output of the TMP390 can be visualized with the output diagram shown in Figure 8-4. It is key

to notice that hysteresis is subtracted from the Channel A threshold and added to the Channel B threshold

values. OUTA remains high until the sensor reaches +90°C where the output goes low, and returns high after the

temperature drops back down to +80°C. OUTB trips when the temperature stays below –25°C and goes low until

the temperature rises above –15°C.

Table 8-1. Example Resistor Settings and Trip Points

CHANNEL

RESISTOR SETTING (kΩ)

HYSTERESIS (°C)

TRIP TEMPERATURE (°C)

SETA

78.7

10

+90

SETB

215

–25

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TMP390

SBOS904A – MAY 2019 – REVISED AUGUST 2020

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