RBias

94 k

5 V

RTMP64

R2

200 k

VOut

R1

10 k

R3

200 k

VTemp

RFB

300 k

VRef

Figure 9-6. Thermal Foldback Using TMP64 Voltage Divider and a Rail-to-Rail Op Amp

The op amp remains high as long as the voltage output is below VRef. When the temperature goes above 110

°C, then the output swings 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 6. This in return

controls the voltage/temperature sensitivity of the circuit. This voltage output is fed into a LED driver IC that

adjusts output current accordingly. The final output voltage used for thermal foldback is VOUT, and is given in

Equation 7. In this example where the knee point is set at 110 °C, the output voltage curve is as shown in Figure

9-7.

TMP64

TEMP

BIAS

BIAS

TMP64

R

V

V

R

R

§

·

u ¨

¸

©

¹

(5)

FB

1

R

G

R

(6)

OUT

TEMP

REF

V

G

V

1

G

V

u

u

(7)

Temperature (qC)

0

25

50

75

100

125

150

0

1

2

3

4

5

6

D014

Figure 9-7. Thermal Foldback Voltage Output Curve

TMP64

SNIS212C – DECEMBER 2019 – REVISED SEPTEMBER 2020

www.ti.com

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