OUT

TEMP

REF

V

G× V

+ (1 + G) × V

FB

1

R

G =

R

TMP61

TEMP

BIAS

TMP61

BIAS

R

V

= V

×

R

+ R

§

·

¨

¸

©

¹

20

TMP61

SBOS921C – DECEMBER 2018 – REVISED SEPTEMBER 2019

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Typical Application (continued)

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 7 (like 110°C, for example). A buffer is used in-between the voltage divider with

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

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

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

and is given in Equation 9. In this example where the knee point is set at 110°C, the output voltage curve is as

shown in Figure 20.

(7)

(8)

(9)