Methods and apparatus for charging a battery in a peripheral device

1. A power manager unit for managing power delivered to a battery powered device, comprising:

a voltage converter unit arranged to convert an external voltage received by an external voltage supply by way of a cable to a supply voltage, wherein the cable includes a number of lines some of which are data lines arranged to form a transmit-receive connection and at least one of which is a power line arranged to carry the external voltage from the external voltage supply to the battery powered device;

a voltage sensor unit coupled to the voltage converter unit for sensing a voltage;

a comparator unit coupled to the voltage sensor unit arranged to generate a switching signal based upon the sensed voltage; and

a switchover circuit coupled to the comparator unit arranged to receive the switching signal, wherein the switchover circuit responds to the received switching signal by connecting the battery powered device and a not fully charged battery to the voltage converter unit such that the supply voltage is provided thereto, wherein when the battery is substantially fully charged, the switchover circuit responds by electrically disconnecting the battery so as to not overcharge the battery.

2. A power management unit as recited in claim 1 , further camprising:

an input current limiter arranged to suppress a power surge resulting from a received external voltage derived from an insertion event of the power line when the power line is carrying the external voltage.

3. A power management unit as recited claim 2 wherein during a power cable removal event, the comparator unit sends a second signal to the switchover circuit.

4. A power management unit as recited in claim 3 , wherein the switchover circuit responds to the second signal by

substantially simultaneously disconnecting the main bus from the power line, and

connecting the battery to the battery powered device.

5. A power management unit as recited in claim 1 , wherein the data lines are separately-shielded twisted transmission type data lines.

6. A power management unit as recited in claim 1 , wherein the cable is a I.E.E.E. 1394 compliant cable.

7. A method for managing power delivered to a battery-operated peripheral device, comprising:

receiving an external voltage from an external voltage supply by way of a cable, wherein the cable includes a number of lines some of which are data lines arranged to form a transmit-receive connection and at least one of which is a power line arranged to carry the external voltage from the external voltage supply to the device;

converting the received external voltage to a supply voltage by a voltage converter unit;

sensing a voltage by a voltage sensor unit coupled to the voltage converter unit;

generating a switching signal based upon the sensed voltage;

receiving the switching signal by a switchover circuit; and

connecting the peripheral device and a not fully charged battery to the voltage converter unit such that the supply voltage is provided thereto in response to the received switching signal, wherein when the battery is substantially fully charged, the switchover circuit responds by electrically isolating the battery from the external voltage supply.

8. A method as recited in claim 7 , further comprising:

suppressing a power surge associated with a power line insertion event.

9. A method far managing power as recited in claim 7 , further comprising:

during a power line removal event, sending a signal to the switchover circuit in response to the power line removal event; and

in response to the signal, substantially simultaneously disconnecting the main bus from the peripheral device and connecting the battery to the peripheral device.

10. A method as recited in claim 7 , wherein the data lines are separately-shielded twisted transmission type data lines.

11. A method as recited in claim 10 , wherein the cable is a I.E.E.E. 1394 compliant cable.

12. An apparatus for managing power delivered to a battery-operated peripheral device, comprising:

means for receiving an external voltage from an external voltage supply by way of a cable, wherein the cable includes a number of lines some of which are data lines arranged to form a transmit-receive connection and at least one of which is a power line arranged to carry the external voltage from the external power supply to the device;

means for converting a received external voltage to a supply voltage;

means for sensing a voltage;

means for generating a switching signal based upon the sensed voltage;

means for receiving the switching signal by a switchover circuit; and

means for connecting the peripheral device and a not fully charged battery to the supply voltage in response to the received switching signal.

13. An apparatus as recited in claim 12 , further comprising:

wherein when the battery is substantially fully charged,

means for electrically isolating the battery from the external voltage supply.

14. An apparatus as recited in claim 12 , further comprising:

means for suppressing a power surge associated wit a power line insertion event;

during a power line removal event,

means for sending a signal to the switchover circuit in response to the power line removal event; and

means for substantially simultaneously disconnecting the main bus from the peripheral device and connecting the battery to the peripheral device.

15. An apparatus as recited in claim 14 , wherein the cable the data lines are separately-shielded twisted transmission type data lines.

16. An apparatus as recited in claim 15 , wherein the cable is a I.E.E.E. 1394 compliant cable.