TMP61 datasheet(16/29 Pages) TI1

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OUT

TEMP

REF

G× V

+ (1 + G) × V

G =

TMP61

TEMP

BIAS

TMP61

BIAS

= V

+ R

TMP61

SBOS921 – DECEMBER 2018

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Typical Application (continued)

rapidly reduced. To better control the temperature/voltage sensitivity of the TMP61, a rail-to-rail operational

amplifier is used. In the example shown in Figure 19, the temperature “knee” where the foldback begins is set by

the reference voltage (2.5 V) at the positive input, and the feedback resistors set the response of the foldback

curve. The foldback knee point may be chosen based on the output of the voltage divider and the corresponding

temperature from Equation 8 like 110°C, for example. A buffer is used in-between the voltage divider with RTMP61

and the input to the op amp to prevent loading and variations in VTEMP.

Figure 19. Thermal Foldback Using TMP61 Voltage Divider and a Rail-to-Rail Op Amp

The op amp will remain high as long as the voltage output is below VRef. When the temperature goes above

110°C, then the output will swing low to the 0-V rail of the op amp. The rate at which the foldback occurs is

dependent on the feedback network, RFB and R1, which varies the gain of the op amp, G, given by Equation 9.

This in return controls the voltage/temperature sensitivity of the circuit. This voltage output is fed into a LED

driver IC that will adjust output current accordingly. The final output voltage used for thermal foldback is VOUT,

and is given in Equation 10. In this example where the knee point is set at 110°C, the output voltage curve is as

shown in Figure 20.

(8)

(9)

(10)

TMP61 Datasheet(PDF) 16 Page - Texas Instruments