Current spike reduction in battery charging devices

1 . An apparatus comprising:

an integrated circuit configured to:

detect a condition that requires an activation of a trickle charge mode of a battery charger, wherein the condition is a detection of a battery voltage being less than a minimum system rail voltage of the battery charger;

in response to the detection, set a reference voltage to an intermediate voltage level, wherein the reference voltage controls a system rail voltage of the battery charger, and the intermediate voltage level is greater than the minimum system rail voltage; and

reduce the reference voltage, at a predefined rate, from the intermediate voltage level to the minimum system rail voltage to regulate the system rail voltage to match the reference voltage, wherein reduction of the reference voltage is performed until the reference voltage reaches the minimum system rail voltage.

2 . The apparatus of claim 1 , wherein the reduction of the reference voltage from the intermediate voltage level to the minimum system rail voltage reduces a current spike flowing into a battery being charged by the battery charger.

3 . The apparatus of claim 1 , wherein the integrated circuit is configured to:

reduce the reference voltage from the intermediate voltage level to another intermediate voltage level; and

reduce the reference voltage from said another intermediate voltage level to the minimum system rail voltage.

4 . The apparatus of claim 1 , wherein the integrated circuit is configured to apply a linear filter to reduce the reference voltage from the intermediate voltage level to the minimum system rail voltage at a predetermined slew rate.

5 . The apparatus of claim 1 , wherein the intermediate voltage is less than a maximum of the system rail voltage.

6 . The apparatus of claim 1 , wherein the integrated circuit further comprises:

a voltage divider configured to divide the system rail voltage to generated a divided voltage; and

a comparator configured to:

compare the divided voltage with a scaled version of the reference voltage; and

output a signal that indicates an amount of adjustment to the system rail voltage for regulating the system rail voltage to match the reference voltage.

7 . The apparatus of claim 6 , wherein the integrated circuit is configured to generate the scaled version of the reference voltage by dividing the reference voltage by a factor that is based on resistance values of at least one resistors that formed the voltage divider.

8 . The apparatus of claim 1 , wherein:

the integrated circuit further comprises a register configured to store a digital value of the intermediate voltage level; and

the integrated circuit is configured to input the digital value to a digital-to-analog converter (DAC) to set the reference voltage to the intermediate voltage level.

9 . A system comprising:

a power stage; and

a battery charging module connected to the power stage, the battery charging module comprises a controller configured to:

control the power stage to output a system rail voltage;

detect a condition that requires an activation of a trickle charge mode of battery charging module, wherein the condition is a detection of a battery voltage being less than a minimum system rail voltage;

in response to the detection, set a reference voltage to an intermediate voltage level, wherein the reference voltage controls the system rail voltage of the battery charging module, and the intermediate voltage level is greater than the minimum system rail voltage; and

reduce the reference voltage, at a predefined rate, from the intermediate voltage level to the minimum system rail voltage to regulate the system rail voltage to match the reference voltage, wherein reduction of the reference voltage is performed until the reference voltage reaches the minimum system rail voltage.

10 . The system of claim 9 , wherein the reduction of the reference voltage from the intermediate voltage level to the minimum system rail voltage reduces a current spike flowing into a battery being charged by the battery charging module.

11 . The system of claim 8 , wherein the controller is configured to:

reduce the reference voltage from the intermediate voltage level to another intermediate voltage level; and

reduce the reference voltage from said another intermediate voltage level to the minimum system rail voltage.

12 . The system of claim 8 , wherein the controller is configured to apply a linear filter to reduce the reference voltage from the intermediate voltage level to the minimum system rail voltage at a predetermined slew rate.

13 . The system of claim 9 , wherein the intermediate voltage is less than a maximum system rail voltage.

14 . The system of claim 9 , further comprising a battery being charged by battery charging module.

15 . A method for regulating a system rail voltage of a battery charger, the method comprising:

detecting a condition that requires an activation of a trickle charge mode of the battery charger, wherein the condition is a detection of a battery voltage being less than a minimum system rail voltage;

in response to the detection, setting a reference voltage to an intermediate voltage level, wherein the reference voltage controls a system rail voltage of the battery charger, and the intermediate voltage level is greater than the minimum system rail voltage; and

reducing the reference voltage, at a predefined rate, from the intermediate voltage level to the minimum system rail voltage to regulate the system rail voltage to match the reference voltage, wherein reduction of the reference voltage is performed until the reference voltage reaches the minimum system rail voltage.

16 . The method of claim 15 , wherein the reduction of the reference voltage from the intermediate voltage level to the minimum system rail voltage reduces of a current spike flowing into a battery being charged by the battery charger.

17 . The method of claim 15 , wherein reducing the reference voltage from the intermediate voltage level to the minimum system rail voltage comprises:

reducing the reference voltage from the intermediate voltage level to another intermediate voltage level; and

reducing the reference voltage from said another intermediate voltage level to the minimum system rail voltage.

18 . The method of claim 15 , further comprising applying a linear filter to reduce the reference voltage from the intermediate voltage level to the minimum system rail voltage at a predetermined slew rate.