This document discusses, among other things, an electronic circuit and method for defaulting to a valid battery supply to power an electronic device. In an example, an electronic circuit can be configured to receive information about the battery supply (e.g., an internal battery), such as the battery supply voltage (V BAT ), and to determine if the battery supply is valid or invalid using the received information (e.g., comparing the V BAT to a threshold). If V BAT is valid, the electronic device can default to receiving power from the battery supply. If V BAT is invalid, the electronic device can receive power from another power supply, such as an external supply.
1. A USB switch circuit configured to receive a supply voltage, to receive a USB bus voltage, and to provide an internal device voltage for operation of the USB switch circuit, the USB switch circuit comprising:
a comparator configured to determine if the supply voltage is valid or invalid based on a comparison of the supply voltage with a reference voltage,
the USB switch circuit being configured to:
provide the internal device voltage for operation of the USB switch circuit using the supply voltage when the supply voltage is valid and the USB bus voltage is greater than the supply voltage; and
provide the internal device voltage for operation of the USB switch circuit using the USB bus voltage when the supply voltage is invalid.
2. The USB switch circuit of claim 1 , wherein the USB switch circuit is configured to receive information from the comparator and to provide the internal device voltage using the supply voltage when the information from the comparator indicates that the supply voltage is above the reference voltage.
3. The USB switch circuit of claim 1 , wherein the supply voltage includes voltage from an internal battery of a mobile device, the USB bus voltage includes voltage from an AC-to-DC converter coupled to a USB port of the mobile device.
4. The USB switch circuit of claim 1 , further comprising:
a switched power supply configured to receive the supply voltage and the USB bus voltage and to provide the internal device voltage using one of the supply voltage or the USB bus voltage using information from the comparator.
5. The USB switch circuit of claim 4 , wherein the switched power supply includes:
first and second switching transistors configured to provide the internal device voltage using the supply voltage; and
third and fourth switching transistors configured to provide the internal device voltage using the USB bus voltage,
the first switching transistor having a drain configured to receive the supply voltage and configured to provide the internal device voltage when the supply voltage is valid, and
the third switching transistor having a drain configured to receive the USB bus voltage and configured to provide the internal device voltage when the supply voltage is invalid.
6. The USB switch circuit of claim 4 , wherein the switched power supply includes:
a first switching transistor configured to provide the internal device voltage using the supply voltage; and
a second switching transistor configured to provide the internal device voltage using the USB bus voltage.
7. The USB switch circuit of claim 1 , further comprising:
a break-before-make circuit configured to trigger supply of the internal device voltage in response to the determination that the supply voltage is valid or invalid.
8. A USB switch circuit configured to receive a supply voltage, to receive a USB bus voltage, and to provide an internal device voltage for operation of the USB switch circuit, the USB switch circuit comprising:
a comparator configured to compare the supply voltage with a reference voltage to determine if the supply voltage is valid or invalid;
a switched power supply configured to receive the supply voltage and the USB bus voltage; and
a break-before-make circuit configured to trigger the switched power supply to provide the internal device voltage using one of the supply voltage or the USB bus voltage using information from the comparator,
the USB switch circuit being configured to control the switched power supply to:
provide the internal device voltage for operation of the USB switch circuit using only the supply voltage when the supply voltage is valid, and
provide the internal device voltage for operation of the USB switch circuit using only the USB bus voltage when the supply voltage is invalid.
9. The USB switch circuit of claim 1 , wherein the supply voltage is a battery voltage.
10. The USB switch circuit of claim 1 , further comprising:
a power supply override circuit configured to change a default configuration of the USB switch circuit.
11. The USB switch circuit of claim 8 , further comprising:
a break-before-make circuit configured to receive the determination that the supply voltage is valid or invalid and configured to control a plurality of switching transistors to provide the internal device voltage using the received determination.
12. The USB switch circuit of claim 8 , wherein the switched power supply includes:
first and second switching transistors configured to provide the internal device voltage using the supply voltage; and
third and fourth switching transistors configured to provide the internal device voltage using the USB bus voltage,
the first switching transistor having a source coupled to a source of the second switching transistor, the first switching transistor having a gate coupled to a gate of the second switching transistor, the first switching transistor having a drain configured to receive the supply voltage, and the drain of the second switching transistor configured to provide the internal device voltage when the supply voltage is valid, and
the third switching transistor having a source coupled to a source of the fourth switching transistor, the third switching transistor having a gate coupled to a gate of the fourth switching transistor, the third switching transistor having a drain configured to receive the USB bus voltage, and the drain of the fourth switching transistor configured to provide the internal device voltage when the supply voltage is invalid.
13. The USB switch circuit of claim 8 , wherein the USB switch circuit is configured to receive information from the comparator and to provide the internal device voltage using the supply voltage when the information from the comparator indicates that the supply voltage is above the reference voltage,
the supply voltage includes voltage from an internal battery of a mobile device, and
the USB bus voltage includes voltage from-an AC-to-DC converter coupled to a USB port of the mobile device.
14. The USB switch circuit of claim 11 , wherein the USB switch circuit is configured to provide the internal device voltage using the supply voltage when the supply voltage is valid and when the USB bus voltage is greater than the supply voltage.
15. A method, comprising:
receiving a supply voltage at a first input of a USB switch circuit;
receiving a USB bus voltage at a second input of the USB switch circuit;
determining, using a comparator, if the supply voltage is valid or invalid based on a comparison of the supply voltage with a reference voltage; and
using the USB switch circuit:
providing an internal device voltage for operation of the USB switch circuit using the supply voltage when the supply voltage is valid; and
providing the internal device voltage for operation of the USB switch circuit using the USB bus voltage when the supply voltage is invalid.
16. The method of claim 15 ,
wherein the providing the internal device voltage using the supply voltage includes providing the internal device voltage using the supply voltage when information from the comparator indicates that the supply voltage is above the reference voltage.
17. The method of claim 15 , wherein the receiving the supply voltage includes receiving the supply voltage from an internal battery of a mobile device; and
the receiving the USB bus voltage includes receiving the USB bus voltage from an AC-to-DC converter coupled to a USB port of the mobile device.
18. The method of claim 15 , wherein the USB switch circuit includes a switched power supply configured to receive the supply voltage and the USB bus voltage and to provide the internal device voltage using one of the supply voltage or the USB bus voltage using information from the comparator.
19. The method of claim 18 , wherein the switched power supply includes:
first and second switching transistors configured to provide the internal device voltage using the supply voltage; and
third and fourth switching transistors configured to provide the internal device voltage using the USB bus voltage.
20. The method of claim 15 , including:
receiving, from the comparator at a break-before-make circuit, the determination if the supply voltage is valid or invalid; and
controlling, using the break-before-make circuit, a plurality of switching transistors to provide the internal device voltage using the received determination.