Over-temperature detector with test mode

Patent metadata

Field	Value
Publication number	US-2016178457-A1
Application number	US-201414574026-A
Country	US
Kind code	A1
Filing date	Dec 17, 2014
Priority date	Dec 17, 2014
Publication date	Jun 23, 2016
Grant date	—

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 second path including a second transistor connected between the voltage node and the ground node, wherein, 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), where V T 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 V T *In(N); and
a measurement circuit, including:
a third transistor including a gate terminal connected to a collector terminal of the second transistor and a source terminal connected to the emitter terminal of the first transistor, and
an output node connected to a drain terminal of the third transistor and 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.

2 . The device of claim 1 , including a resistor coupled between the 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 3 , including a first current source connected between the first transistor and the ground node and a second current source connected between the second transistor and the ground node.

5 . The device of claim 4 , 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.

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 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.

8 . The device of claim 1 , wherein the measurement circuit includes a switch coupled to the third transistor of the measurement circuit, the switch being configured to selectively activate and deactivate the measurement circuit.

9 . A device, comprising:
a temperature detection circuit, including:
a first path including a first transistor connected between a voltage node and a ground node,
a second path including a second transistor connected between the voltage node 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 connected to an emitter terminal of the first transistor, and
a second output node 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:
determine an ambient temperature of the temperature detection circuit,
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.

10 . The device of claim 9 , including a resistor coupled between an emitter terminal of the second transistor and a base terminal of the second transistor.

11 . The device of claim 9 , 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.

12 . The device of claim 11 , including a first current source connected between the first transistor and the ground node and a second current source connected between the second transistor and the ground node.

13 . The device of claim 12 , 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.

14 . The device of claim 9 , 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.

15 . The device of claim 9 , including an amplifier connected between the collector terminal of the second transistor and the gate terminal of the third transistor.

16 . A device, comprising:
an output node configured to generate an output voltage that is proportional to a difference between a temperature threshold of a temperature detector and an ambient temperature of the temperature detector; a voltage node; a ground node; at least two temperature detectors, each temperature detector including:
a first path including a first transistor connected between the voltage node and the ground node,
a second path including a second transistor connected between the voltage node and the ground node,
a thermal shutdown signal output configured to output a first voltage value when an ambient temperature of the temperature detector is greater than a temperature threshold and a second voltage value when the ambient temperature of the temperature detector is less than the temperature threshold,
a third transistor including a gate terminal connected to a collector terminal of the second transistor and a source terminal connected to an emitter terminal of the first transistor, and
a switch coupled to the third transistor and being configured to selectively connect a drain terminal of the third transistor to the output node; and
a controller configured to:
close the switch of one of the at least two temperature detectors,
measure the output voltage at the output node, and
determine the temperature threshold of the one of the at least two temperature detectors using the output voltage at the output node and an ambient temperature of the one of the at least two temperature detectors.

17 . The device of claim 16 , wherein the one of the at least two temperature detectors includes a resistor coupled between an emitter terminal of the second transistor of the one of the at least two temperature detectors and a base terminal of the second transistor of the one of

Assignees

• Pigott John M
• Freescale Semiconductor 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

• G01K7/16

  using resistive elements · CPC title