TMP01

REV. C

–6–

Temperature Hysteresis

The temperature hysteresis is the number of degrees beyond the

original setpoint temperature that must be sensed by the TMP01

before the setpoint comparator will be reset and the output dis-

abled. Figure 2 shows the hysteresis profile. The hysteresis is

programmed by the user by setting a specific load on the refer-

called the hysteresis current, which is mirrored internally and

fed to a buffer with an analog switch.

LO

HI

OUTPUT

VOLTAGE

OVER, UNDER

TEMPERATURE

HYSTERESIS

LOW

HYSTERESIS HIGH =

HYSTERESIS LOW

T

SETLOW

T

SETHIGH

HYSTERESIS

HIGH

Figure 2. TMP01 Hysteresis Profile

After a temperature setpoint has been exceeded and a compara-

tor tripped, the buffer output is enabled. The output is a cur-

rent of the appropriate polarity which generates a hysteresis

offset voltage across an internal 1000

Ω resistor at the compara-

tor input. The comparator output remains “on” until the volt-

age at the comparator input, now equal to the temperature

sensor voltage VPTAT summed with the hysteresis offset, has

returned to the programmed setpoint voltage. The comparator

then returns LOW, deactivating the open-collector output and

disabling the hysteresis current buffer output. The scale factor

for the programmed hysteresis current is:

µA/°C + 7 µA

Thus since VREF = 2.5 V, with a reference load resistance of

357 k

Ω or greater (output current 7 µA or less), the temperature

setpoint hysteresis will be zero degrees. See the temperature

programming discussion below. Larger values of load resistance

will only decrease the output current below 7

µA and will have

no effect on the operation of the device. The amount of hyster-

esis is determined by selecting a value of load resistance for

VREF, as shown below.

Programming the TMP01

In the basic fixed-setpoint application utilizing a simple resistor

ladder voltage divider, the desired temperature setpoints are

programmed in the following sequence:

1. Select the desired hysteresis temperature.

3. Select the desired setpoint temperatures.

4. Calculate the individual resistor divider ladder values needed

to develop the desired comparator setpoint voltages at

SETHIGH and SETLOW.

The hysteresis current is readily calculated, as shown. For

the VPTAT scale factor of 5 mV/K = 5 mV/(

°C + 273.15),

which is 1.49 V for +25

°C. We then calculate the divider resis-

tors, based on those setpoints. The equations used to calculate

the resistors are:

°C)

°C)

R1 (k

Ω) = (V

R2 (k

Ω) = (V

R3 (k

Ω) = V

1

2

3

4

8

7

6

5

(V

VREF

– V

SETHIGH

)/I

VREF

= R1

TMP01

(V

SETHIGH

– V

SETLOW

)/I

VREF

= R2

V

SETLOW

/I

VREF

= R3

V

SETHIGH

V

SETLOW

V

VREF

= 2.5V

I

VREF

GND

V+

VPTAT

UNDER

OVER

Figure 3. TMP01 Setpoint Programming

The total R1 + R2 + R3 is equal to the load resistance needed

to draw the desired hysteresis current from the reference, or

The formulas shown above are also helpful in understanding the

calculation of temperature setpoint voltages in circuits other

than the standard two-temperature thermostat. If a setpoint

function is not needed, the appropriate comparator should be

disabled. SETHIGH can be disabled by tying it to V+, SET-

LOW by tying it to GND. Either output can be left unconnected.

218

248

273

298

323

348

373

398

–55

–25 –18

0

25

50

75

100

125

–67

–25

0

32 50

77

100

150

200 212

257

VPTAT

K

1.09

1.24

1.365

1.49

1.615

1.74

1.865

1.99

Figure 4. Temperature—VPTAT Scale