Power failure detection circuit with fast drop response

• US 7,312,644 B2
• Filed: 12/14/2005
• Issued: 12/25/2007
• Est. Priority Date: 12/15/2004
• Status: Active Grant

• Current Assignee: Atmel Corporation (Microchip Technology Incorporated)
• Original Assignee: Atmel Nantes SA (Microchip Technology Incorporated)
• Inventors: Messager, Philippe
• Primary Examiner(s): Lam, Tuan T.
• Assistant Examiner(s): Hernandez, William
• Application Number:
  US11/302,954
• Publication Number:
  US 20060170467A1
• Time in Patent Office: 741 Days
• Field of Search: 327/142, 327/143, 327/198
• US Class Current: 327/143
• CPC Class Codes: H03K 17/223 in field-effect transistor switches

Abstract

A device is provided for resetting an integrated circuit generating a reset signal after a power supply voltage drop to a very low level has been detected. Such a device includes at least one control means, the state of which (conducting or non-conducting) is controlled by a control voltage equal to the difference between the power supply voltage and a predetermined offset voltage, such that if the control voltage is less than or equal to a threshold, the control means authorizes activation of the means for generating a reset signal.

Claims

1. A resetting device comprising:

detection means for detecting a drop in a power supply voltage received by the said device; and

means for generating a reset signal, activated after a drop in the said power supply voltage has been detected by the said detection means, wherein the said detection means comprise;

a first control means itself comprising a first transistor forming a first switch and cooperating with energy storing means included within the said detection means, the said first transistor comprising a control element on which a first control voltage is applied, which is equal to the difference between the said power supply voltage and a first predetermined offset voltage, such that;

if the said first control voltage is greater than a first threshold, the said first transistor is in a non-conducting state, in which the said first transistor authorizes storage of energy in the said storage means; and

if the said first control voltage is less than or equal to the said first threshold, the said first transistor is in a conducting state in which the said first transistor authorizes the said energy storage means to release the said energy, so as to activate the said generation means;

a second control means itself comprising a second transistor forming a second switch and cooperating with a first current source included within the said detection means, the said second transistor comprising a control element on which a second control voltage is applied, which is equal to the difference between the said power supply voltage and a second predetermined offset voltage, such that;

if the said second control voltage is greater than a second threshold, the said second transistor is in a conducting state, in which the said second transistor prevents a current generated by the said first current source from reaching the said generation means; and

if the said second control voltage is less than or equal to the said second threshold, the said second transistor is in a non-conducting state, in which the said second transistor directs the current generated by the said first current source to the said means for generating a reset signal, so as to activate the said generation means.

2. The resetting device according to claim 1, wherein the said first threshold is equal to the difference between a determined voltage applied to a source of the said first transistor and a threshold voltage of the said first transistor.

3. The resetting device according to claim 1, wherein the said first predetermined offset voltage, denoted VX1, is such that:

0≦

VX1 <

VCCn −

(VS-VT) where

VCCn is a nominal value of the said power supply voltage;

VT is a threshold voltage of the said first transistor; and

VS is a determined voltage applied to a source of the said first transistor.

4. The resetting device according to claim 1, wherein the said energy storage means comprise a third transistor used as a filtering capacitance.

5. The resetting device according to claim 1, wherein the said second threshold is equal to a threshold voltage of the said second transistor.

6. The resetting device according to claim 1, wherein the said second predetermined offset voltage, denoted VX2, is such that:

0≦

VX2<

VCCn−

VT,

where;

VCCn is a nominal value of the said power supply voltage; and

VT is a threshold voltage of the said second transistor.

7. The resetting device according to claim 1, wherein the said first current source comprises a current mirror powered by the said power supply voltage.

8. The resetting device according to claim 1, wherein the said second transistor comprises:

a gate forming the said control element of the second transistor;

a source connected to the ground; and

a drain connected to a mid-point between the said first current source and the said generation means.

9. The resetting device according to claim 1, wherein the said first threshold is less than the said second threshold.

10. The resetting device according to any one of claims 1, wherein the said detection means also comprise a third control means, itself comprising:

means for comparing a voltage proportional to the said power supply voltage (div) with a determined reference voltage (VBGP), the said comparison means generating a resultant voltage (VDIFF) that depends on the result of the comparison;

a fourth transistor forming a third switch and cooperating with a second current source, that may or may not be coincident with the said first current source, the said fourth transistor comprising a control element on which the said resultant voltage is applied, such that;

if the said resultant voltage (VDIFF) is greater than a third threshold, the said fourth transistor is in a conducting state, in which the said fourth transistor prevents a current generated by the said second current source from reaching the said generation means;

if the said resultant voltage (VDIFF) is less than or equal to the said third threshold, the said fourth transistor is in a non-conducting state, in which the said fourth transistor directs the current generated by the said second current source to the said means for generating a reset signal, so as to activate the said generation means.

11. The resetting device according to claim 10, wherein the said second threshold is less than the said third threshold.

12. The resetting device according to claim 10, wherein the said first threshold is less than the said third threshold.

13. The resetting device according to claim 10, wherein the fourth transistor is mounted with respect to the second transistor such that the said second switch formed by the second transistor behaves like a master switch with respect to the third switch formed by the fourth transistor, such that if the second transistor is in the said non-conducting state, the said generation means are activated regardless of the state of the fourth transistor.

14. The resetting device according to any one of claims 10, wherein the said fourth transistor comprises:

a gate forming the said control element of the fourth transistor;

a source connected to the drain of the second transistor; and

a drain connected to a mid-point between the said first current source and the said generation means.

15. An electronic circuit comprising the resetting device of claim 1.