NCT51, NCT52

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3

PIN DESCRIPTION

NCT51

NCT52

Name

Description

1,2

1,2

GND

Ground. Ground both pins together close to the chip. Pin 2 provides the lowest thermal

resistance to the die.

3

3

HYST

Hysteresis Input. Connect HYST to GND for +2

hysteresis.

4

4

to GND.

5

–

TOVER

Open–Drain, Active–Low Output. TOVER goes low when the die temperature exceeds the

factory–programmed temperature threshold. Connect to a 100 K

Ω pull–up resistor. May be

–

5

TOVER

Push/Pull Active–High Output. TOVER goes high when the die temperature exceeds the

factory–programmed temperature threshold.

–

–

TUNDER

Open–Drain, Active–Low Output. TUNDER goes low when the die temperature goes below

the factory–programmed temperature threshold. Connect to a 100 K

Ω pull–up resistor. May

–

–

TUNDER

Push/Pull Active–High Output. TUNDER goes high when the die temperature is below the

factory–programmed temperature threshold.

Typical Operating Circuit

GND

NCT52

GND

GND HYST

TOVER

INT

µP

100 pF

+2.7 V to +5.5 V

DETAILED DESCRIPTION

The NCT51 and NCT52 integrate a temperature sensor

with a factory–programmed threshold switch. A logic signal

is asserted when the die temperature crosses the factory

programmed threshold. An external hysteresis input pin

allows the user to select either 2

°C or 10°C hysteresis to give

further flexibility to the design of the application. The NCT51

and NCT52 are intended for a temperature range from 45

°C

to 115

°C in a 10°C increment. The NCT51 has an open drain

output and the NCT52 has a push/pull output stage.

The NCT51 is intended for applications with a

microprocessor reset input. The NCT52 is intended for

applications of turning on a fan or heater element.

Hysteresis Input

To prevent the output from “chattering’’ at or near the trip

point temperature, a selectable HYST input pin is provided.

Hysteresis can be externally selected at 2

°C (HYST = GND)

or 10

HYST input pin. Do not let the HYST pin float as this could

cause increase supply current. The hysteresis does not

depend on the part’s programmed trip threshold.

Table 1. Factory–Programmed Threshold Range

Part Number

NCT51

+45

NCT52

+45

Thermal Considerations

With a very low 17

µA supply current, the NCT51 and

NCT52 dissipates very little power. Thus, the die

temperature is basically the same as the package

temperature. To minimize the error in temperature readings,

the load current should be limited to a few milliamps. As an

example, the typical thermal resistance of a 5–Pin SOT–23A

package is 140

°C/W. If the NCT51 had to sink 1.0 mA, and

the output voltage is guaranteed to be less than 0.3 V, then

an additional 0.3 mW of power is dissipated within the IC.

This corresponds to a 0.042

°C rise in die temperature in the

5–Pin SOT–23A.