Over-temperature detector with test mode

Patent metadata

Field	Value
Publication number	US-9939335-B2
Application number	US-201414574026-A
Country	US
Kind code	B2
Filing date	Dec 17, 2014
Priority date	Dec 17, 2014
Publication date	Apr 10, 2018
Grant date	Apr 10, 2018

Abstract

A device for over-temperature detection having a test mode is presented. The device includes a temperature detection circuit having first and second transistors. The temperature detection circuit is configured so that when an ambient temperature of the temperature detection circuit is less than a temperature threshold, a voltage at an emitter terminal of the second transistor is less than a voltage at an emitter terminal of the first transistor minus V T *In(N), and when the ambient temperature of the temperature detection circuit is greater than the temperature threshold, the voltage at the emitter terminal of the second transistor is greater than a voltage at the emitter terminal of the first transistor minus V T *In(N). The device includes a measurement circuit configured to generate an output voltage that is proportional to a difference between the temperature threshold of the temperature detection circuit and the ambient temperature of the temperature detection circuit.

First claim

What is claimed is:

1. A device, comprising:
a temperature detection circuit, including:
a first path including:
a first transistor connected between a voltage node and a ground node, and
a first current source connected between the first transistor and the ground node,

a second path including:
a second transistor connected between the voltage node and the ground node, and
a second current source connected between the second transistor and the ground node, and

a first output node configured to output a first voltage value when an ambient temperature of the temperature detection circuit is greater than a temperature threshold and a second voltage value when the ambient temperature of the temperature detection circuit is less than the temperature threshold;

a measurement circuit, including:
a third transistor including a gate terminal connected to a collector terminal of the second transistor and a source terminal directly connected to an emitter terminal of the first transistor, and
a second output node directly connected to a drain terminal of the third transistor, the second output node being configured to generate an output voltage that is proportional to a difference between the temperature threshold of the temperature detection circuit and the ambient temperature of the temperature detection circuit; and

a controller configured to:
measure the output voltage at the second output node of the measurement circuit, and
determine the temperature threshold of the temperature detection circuit using the output voltage at the second output node of the measurement circuit and the ambient temperature of the temperature detection circuit.

2. The device of claim 1 , including a resistor coupled between an emitter terminal of the second transistor and a base terminal of the second transistor.

3. The device of claim 1 , including a first resistor connected between the first transistor and the voltage node and a second resistor connected between the second transistor and the voltage node.

4. The device of claim 1 , wherein a current through the first transistor is about equal to a current through the second transistor when a first current generated by the first current source has a magnitude of about twice that of a magnitude of a second current generated by the second current source.

5. The device of claim 1 , wherein the measurement circuit includes a switch coupled to the third transistor of the measurement circuit, and the controller is configured to operate the switch to activate and deactivate the measurement circuit.

6. The device of claim 1 , including an amplifier connected between the collector terminal of the second transistor and the gate terminal of the third transistor.

7. The device of claim 1 , including a resistor coupled between the second output node and the ground node.

8. The device of claim 1 , wherein:
when an ambient temperature of the temperature detection circuit is less than the temperature threshold, a voltage at an emitter terminal of the second transistor is less than a voltage at an emitter terminal of the first transistor minus VT*In(N), where VT is thermal voltage and N is a ratio of a current density of the first transistor to a current density of the second transistor, and when the ambient temperature of the temperature detection circuit is greater than the temperature threshold, the voltage at the emitter terminal of the second transistor is greater than a voltage at the emitter terminal of the first transistor minus VT*In(N).

9. The device of claim 1 , further comprising:
a fourth transistor, the fourth transistor including
a source terminal connected to a base terminal of the first transistor and a base terminal of the second transistor; and
a gate terminal connected to a collector terminal of the first transistor.

10. The device of claim 1 , further comprising:
a second temperature detector including:
a third path including a fourth transistor connected between the voltage node and the ground node,
a fourth path including a fifth transistor connected between the voltage node and the ground node,
a sixth transistor including a gate terminal connected to a collector terminal of the fifth transistor and a source terminal connected to an emitter terminal of the fourth transistor, and
a switch coupled to the sixth transistor and being configured to selectively connect a drain terminal of the sixth transistor to the second output node.

Assignees

• Pigott John M
• Nxp Usa Inc

Inventors

• Pigott John M

Classifications

• G01K3/005

  Circuits arrangements for indicating a predetermined temperature (fire detection G08B17/00) · CPC title

• G01K15/007 Primary

  Testing · CPC title