Current limit control in hot swap controllers

1. A device configured to automatically adjust a current limit and to control an electronic switch between a power supply configured to generate an input voltage and to supply an output voltage to a load, the device comprising:

a current limit circuit configured to generate a current limit signal and automatically adjust the current limit signal using:

a voltage proportional to a current to the load measured by a sensing circuit; and

at least one of the input voltage and the output voltage;

the current limit circuit including:

a fixed reference voltage source configured to be coupled to a resistive network, wherein the resistive network is configured to set a current limit voltage; and

an arithmetic circuit configured to use the current limit voltage and the fixed reference voltage source to generate a reference voltage that automatically adjusts in response to a change in at least one of the input voltage and the output voltage; and

a control circuit coupled to the electronic switch and configured to receive the current limit signal and control operation of the electronic switch using the current limit signal.

2. The device of claim 1 , the device further comprising:

a comparator circuit configured to:

compare the voltage proportional to the measured current to the automatically adjusting reference voltage; and

output the current limit signal to the control circuit using the comparison.

3. The device of claim 2 ,

wherein the current limit signal output by the comparator circuit is a digital current limit signal.

4. The device of claim 1 , wherein the fixed reference voltage source includes a low dropout regulator.

5. The device of claim 1 , wherein the resistive network is external or internal to the device.

6. The device of claim 1 , wherein the arithmetic circuit comprises at least one operational amplifier.

7. The device of claim 1 , comprising:

a buffer coupled to the arithmetic circuit, the buffer configured to reduce current flow into the device.

8. The device of claim 1 , wherein the electronic switch comprises a plurality of electronic switches.

9. A method to automatically adjust a current limit and to control an electronic switch between a power supply configured to generate an input voltage and to supply an output voltage to a load, the method comprising:

measuring a current to the load and generating a voltage proportional to the measured current;

generating a current limit signal representing a current limit using:

the voltage proportional to the measured current; and

at least one of an input voltage and an output voltage;

setting a current limit voltage;

generating a reference voltage that automatically adjusts in response to the change in at least one of the input voltage and the output voltage by using the current limit voltage and a fixed reference voltage source; and

controlling operation of the electronic switch using the current limit signal.

10. The method of claim 9 , further comprising:

automatically adjusting the current limit signal in response to a change in at least one of the input voltage and an output voltage.

11. The method of claim 9 , wherein the fixed reference voltage source comprises

a low dropout regulator.

12. The method of claim 9 , wherein generating a reference voltage that automatically adjusts in response to the change in at least one of the input voltage and the output voltage by using the current limit voltage and a fixed reference voltage source includes:

configuring an operational amplifier to use the current limit voltage and the fixed reference voltage to generate the reference voltage that automatically adjusts in response to the change in at least one of the input voltage and the output voltage.

13. The method of claim 9 , wherein controlling operation of the electronic switch using the current limit signal comprises:

adjusting a voltage on a terminal of a transistor.

14. The method of claim 9 , further comprising:

comparing the voltage proportional to the current to the load to the automatically adjusting reference voltage; and

outputting the current limit signal to the control circuit using the comparison.

15. The method of claim 14 , wherein outputting the current limit signal includes outputting a digital current limit signal.

16. A device configured to automatically adjust a current limit and to control an electronic switch between a power supply configured to generate an input voltage and to supply an output voltage to a load, the device comprising:

means for measuring a current to the load and generating a voltage proportional to the measured current;

means for generating a current limit signal representing a current limit using:

the voltage proportional to the measured current; and

at least one of an input voltage and an output voltage; and

means for setting a current limit voltage;

means for generating a reference voltage that automatically adjusts in response to the change in at least one of the input voltage and the output voltage by using the current limit voltage and a fixed reference voltage source; and

means for controlling operation of the electronic switch using the current limit signal.

17. The device of claim 16 , further comprising:

means for comparing the voltage proportional to the current to the load to the automatically adjusting reference voltage; and

means for outputting the current limit signal to a control circuit using the comparison.