CIRCUIT AND METHOD FOR AVOIDING SHUTDOWN OF A PORTABLE DEVICE DUE TO A FALSE LOW VOLTAGE CONDITION

• US 20160036260A1
• Filed: 07/31/2014
• Published: 02/04/2016
• Est. Priority Date: 07/31/2014
• Status: Active Grant

• Current Assignee: Motorola Solutions, Inc.
• Original Assignee: Motorola Solutions, Inc.
• Inventors: Nunez, Diego I, Bartels, Peter J
• Granted Patent: US 9,472,967 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: B60L 2210/14 Boost converters
• CPC Class Codes: H02J 7/0048 Detection of remaining charge capacity or state of charge [SOC]
• CPC Class Codes: H02J 7/0063 with circuits adapted for supplying loads from the battery
• CPC Class Codes: H02J 7/007184 in response to battery voltage gradient
• CPC Class Codes: Y02T 10/70 Energy storage systems for electromobility, e.g. batteries
• CPC Class Codes: Y02T 10/72 Electric energy management in electromobility

Abstract

A method and circuit for avoiding a low voltage shutdown in a portable device due to a low voltage falsely indicating a discharged battery employs an input current sensing circuit to determine when a high current is being drawn by the portable device. When the portable device is drawing a high current from the battery, the shutdown function is at least temporarily suppressed. If, during the high current event, the battery behavior indicates that it is actually near fully discharged, the shutdown functionality can be enabled to shut down the portable device.

Claims

1. A power management system for a portable device, comprising:

a power management controller that compares an input voltage to a shutdown threshold and initiates a shutdown of the portable device when the input voltage falls below the shutdown threshold;

a voltage monitoring switch having an output that provides the input voltage to the power management controller, a first input connected to a positive battery terminal of the portable device, a second input connected to a voltage source that is higher than the shutdown threshold, and a control input, wherein the voltage monitoring switch alternately connects either the first input or the second input to the output responsive to a control signal provided to the control input; and

a current sense circuit that provides the control signal to the voltage monitoring switch based on an input current through the positive battery terminal of the portable device, wherein when the input current exceeds a high current threshold, the circuit provides the control signal at a level that causes the voltage monitoring switch to connect the second input to the output, and wherein the control signal is provided to cause the voltage monitoring switch to connect the first input to the output otherwise.

2. The power management system of claim 1, wherein the current sense circuit comprises:

a current sensing circuit that produces a current sense voltage that is proportional to current drawn through the positive battery terminal; and

a comparator that compares the current sense voltage to a current sense threshold that corresponds to the high current threshold.

3. The power management system of claim 1, wherein the current sensing circuit is a portion of a conductor runner on a circuit board of the portable device.

4. The power management system of claim 1, further comprising a timer that times a high current period when current through the positive battery terminal is above the high current threshold, and wherein when the high current period exceeds a maximum high current time period the power management circuit shuts the portable device down.

5. The power management system of claim 1, further comprising:

a boost converter that provides a boost voltage from a battery voltage provided at the positive battery terminal;

a high voltage circuit powered by the boost converter;

a battery voltage circuit;

a boost switch that is responsive to the control signal provided by the current sense circuit and connect the battery voltage circuit to a battery voltage provided by the positive battery terminal when the input current is below the high current threshold and connects the battery voltage circuit to the boost voltage provided by the boost converter when the input current exceeds the high current threshold.

6. The power management system of claim 1, further comprising a controller that receives the control signal and when the control signal indicates the input current exceeds the high current threshold the controller determines a change in the battery voltage over a period of time and enables the power management circuit to commence shutdown of the portable device when the change in voltage exceeds a voltage drop threshold.

7. The power management system of claim 1, further comprising a controller that receives the control signal and when the control signal indicates the input current exceeds the high current threshold the controller changes operation of at least one auxiliary circuit to reduce the current usage of the auxiliary circuit.

8. A method for avoiding shutdown of a portable device due to a false low battery voltage condition, comprising:

detecting an input current from a battery into portable device being above a high current threshold; and

modifying, responsive to detecting the input current being above the high current threshold, a voltage sensing input of a power management controller of the portable device from a battery voltage to a voltage source that provides a voltage level above a shutdown threshold level, wherein the power management controller initiates a shutdown process of the portable device when a voltage at the voltage sensing input of the power management controller is below the shutdown threshold.

9. The method of claim 8, wherein modifying the voltage sensing input comprises asserting an output of a current sensing circuit to a control input of a voltage monitoring switch that alternately connect either the battery voltage or the voltage source to the voltage sensing input of the power management controller.

10. The method of claim 8, further comprising:

commencing a high current timer upon detecting the input current to be above the high current threshold; and

when the high current timer expires during a period where the input current remains above the high current threshold, reverting the voltage sensing input of the power management controller to be connected to the battery voltage.

11. The method of claim 8, wherein detecting the input current comprises detecting a voltage differential across a segment of a conductor runner on a circuit board of the portable device.

12. The method of claim 8, further comprising switching a battery voltage circuit from the battery voltage to a boost voltage that is higher than the battery voltage upon detecting the input current being above the high current threshold.

13. The method of claim 8, further comprising changing operation of at least one auxiliary circuit to reduce the current demand of the auxiliary circuit.

14. The method of claim 8, further comprising:

determining a rate of drop of the battery voltage while detecting the input current being above the high current threshold; and

when the rate of drop of the battery voltage exceeds a voltage change threshold, enabling the power management controller to initiate the shutdown process.

15. The method of claim 8, wherein the detecting and modifying are performed only when the battery voltage is below a monitoring threshold, which is higher than the shutdown threshold.

16. A portable device, comprising:

a positive battery terminal and a negative battery terminal, wherein a battery voltage is present between the positive battery terminal and the negative battery terminal when a battery is connected to the portable device;

a current sense circuit having an output that asserts a control signal when an input current through the positive battery terminal of the portable device exceeds a high current threshold;

a power management controller that compares an input voltage to a shutdown threshold and initiates a shutdown of the portable device when the input voltage falls below the shutdown threshold;

a voltage monitoring switch having a first input connected to the positive battery terminal, a second input connected to a voltage source that provides a voltage higher than the shutdown threshold, an output that provides the input voltage to the power management circuit, and a control input that receives the control signal, wherein the voltage monitoring switch normally connects the battery terminal as the input voltage to the power management circuit and switches the input voltage to the voltage source when the control signal is asserted.

17. The portable device of claim 16, further comprising a timer that times a high current period when current through the positive battery terminal is above the high current threshold, and wherein when the high current period exceeds a maximum high current time period the power management circuit shuts the portable device down.

18. The portable device of claim 16, further comprising:

a boost converter that provides a boost voltage from a battery voltage provided at the positive battery terminal;

a high voltage circuit powered by the boost converter;

a battery voltage circuit;

a boost switch that is responsive to the control signal provided by the current sense circuit and connect the battery voltage circuit to a battery voltage provided by the positive battery terminal when the input current is below the high current threshold and connects the battery voltage circuit to the boost voltage provided by the boost converter when the input current exceeds the high current threshold.

19. The portable device of claim 16, further comprising a controller that receives the control signal and when the control signal indicates the input current exceeds the high current threshold the controller determines a change in the battery voltage over a period of time and enables the power management circuit to commence shutdown of the portable device when the change in voltage exceeds a voltage drop threshold.

20. The portable device of claim 16, further comprising a controller that receives the control signal and when the control signal indicates the input current exceeds the high current threshold the controller changes operation of at least one auxiliary circuit to reduce the current usage of the auxiliary circuit.