Voltage ratio control circuit for use during power transitions

• US 6,313,693 B1
• Filed: 07/10/2000
• Issued: 11/06/2001
• Est. Priority Date: 07/10/2000
• Status: Expired due to Term

• Current Assignee: SMART Embedded Computing, Inc. (Smart Global Holdings Incorporated)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Kelm, Sigurd Arnulf
• Primary Examiner(s): KIM, JUNG H
• Application Number:
  US09/613,326
• Time in Patent Office: 484 Days
• Field of Search: 307/19, 307/28, 307/45, 307/47, 307/48, 307/74, 307/75, 327/540, 327/530
• US Class Current: 327/540
• CPC Class Codes: G05F 1/569 for protection

Abstract

An electronics module (FIG. 1, 30) requires two distinct voltage inputs (V₁, V₂) and can be damaged when the difference between the two voltages exceeds a maximum value during power up. Additionally the electronics module (30) can be damaged during a power down transition when the difference between the two voltages exceeds a maximum negative value. A voltage ratio control circuit (FIG. 8) which includes at least one diode (D1), a capacitor (C1) whose value is proportional to the product of the value of the second voltage source (V2) and the value of the sum of any decoupling capacitances (C2) divided by the difference between the two input voltages is used to reduce the difference between the two voltages. This prevents damage to the electronic module (FIG. 1, 30) during power up and power down transitions caused by excessive voltage differences in the two voltage inputs (V₁ and V₂).

Claims

1. An electronic circuit for controlling a ratio between two voltages during a power up condition, comprising:

a first input which accepts a first of said two voltages;

a second input which accepts a second of said two voltages;

at least one diode coupled between said first and second inputs for influencing said second input using said first input;

a first capacitor coupled between said first and second inputs for controlling a voltage ratio between said first and second inputs during said power up condition; and

a second capacitor coupled between said second input and a ground, said second capacitor receiving a charge from said at least one diode.

2. The electronic circuit of claim 1, wherein the value of said first capacitor is proportional to the value of said second capacitor.

3. The electronic circuit of claim 2, wherein the value of said first capacitor is also proportional to the value of said second of said two voltages divided by the difference between said first and second of said two voltages.

4. The electronic circuit of claim 1, additionally comprising a resistor coupled between said second input and a ground, said resistor conveying a charge from said second capacitor to said ground.

5. A circuit for controlling a ratio between at least two voltages during a power state transition, comprising:

a first input which accepts a first of said at least two voltages;

a second input which accepts a second of said at least two voltages;

means for coupling current between said first and second inputs, wherein said means comprises at least one diode;

a first capacitor coupled between said first and second inputs for controlling a voltage ratio between said first and second inputs during said power state transition; and

a second capacitor coupled between said second input and a ground, said second capacitor receiving a charge from said at least one diode.

6. The circuit of claim 5 wherein the value of said first capacitor is proportional to the value of said second capacitor multiplied by the value of said second of said at least two voltages and divided by the difference of said second of said at least two voltages subtracted from said first of said at least two voltages.

7. The electronic circuit of claim 5, additionally comprising a resistor coupled between said second input and a ground, said resistor conveying a charge from said second capacitor to said ground.