Current mode DC/DC converter with controlled output impedance

Abstract

A DC/DC converter has an output voltage and sources an output current to a load. The DC/DC converter includes an error amplifier with a reference input and a summing input. The reference input is electrically connected to a reference voltage. The summing input is electrically connected to the output voltage and the output current. The summing input is configured for adding together the output voltage and the output current. The error amplifier issues an error signal and adjusts the error signal dependent at least in part upon the output voltage and the output current. A comparator receives the error signal. The comparator has a ramp input electrically connected to a voltage ramp signal. The comparator issues an output signal that is based at least in part upon said error input. A power switch has an on condition and an off condition, and supplies dc current to the load when in the on condition. The power switch has a control input electrically connected to the comparator output signal. The power switch is responsive to the control input to change between the on condition and the off condition to thereby adjust the output current of the DC/DC converter.

1. A DC/DC converter having an output voltage and sourcing an output current to a load, said DC/DC converter comprising:
 an error amplifier having a reference input and a summing input, said reference input being electrically connected to a reference voltage, said summing input being electrically connected to each of the output voltage and the output current of said DC/DC converter, said summing input configured for adding together the output voltage and the output current, said error amplifier issuing an error signal and being configured for adjusting said error signal dependent at least in part upon the output voltage and the output current;   a comparator receiving said error signal, said comparator having a ramp input electrically connected to a voltage ramp signal, said comparator having a comparator output signal, said comparator output signal based at least in part upon said error input; and   a power switch having an on condition and an off condition, said power supply configured for supplying dc current to the load when in said on condition, said power switch having a control input electrically connected to said comparator output signal, said power switch being responsive to said comparator output signal to change between said on condition and said off condition to thereby adjust the output current of said DC/DC converter.   
     
     
       2. The DC/DC converter of  claim 1 , wherein said power switch comprises at least one power transistor configured for supplying the output current to the load. 
     
     
       3. The DC/DC converter of  claim 1 , further comprising:
 an inductor electrically connected between a first circuit node and the load, said first circuit node being disposed intermediate said power switch and the load, said inductor carrying the output current to the load;   a diode electrically connected between said first circuit node and ground, said diode being configured for carrying return load current, said return load current flowing from the load when said power switch is in said off condition; and   a current sensor having a current input, a current output, and a sensing output, the output current flowing into said current input and out of said current output, said current output being electrically connected to said first circuit node, said current sensor being configured for sensing at least one of said load current and said return load current and for issuing a sensor output signal representative of the output current, said sensor output signal being electrically coupled to said summing input of said error amplifier.   
     
     
       4. The DC/DC converter of  claim 3 , further comprising a voltage divider, said voltage divider having a divider input and a divider output, said divider input being electrically connected to the output voltage and to said sensing output of said current sensor, said divider output being electrically connected to said summing input of said error amplifier. 
     
     
       5. The converter of  claim 1 , further comprising a summing circuit including a voltage divider having a first resistor electrically connected between said summing input of said error amplifier and the output voltage, a second resistor electrically connected between said summing input and said sensing output of said current sensor, and a third resistor electrically connected between said summing input and ground. 
     
     
       6. The converter of  claim 1  further comprising a summing circuit, said summing circuit including a voltage divider having an output voltage resistor electrically connected between said summing input of said error amplifier and the output voltage, a voltage to current converter for converting a voltage signal representative of the output current to a current signal, said voltage to current converter being electrically coupled to said summing input, and a second resistor connected between said summing input and ground. 
     
     
       7. A method of providing droop in the output voltage of a DC/DC converter having an output current, said method comprising the steps of:
 sensing the output current to thereby determine an output current signal representative of the output current;   further sensing the output voltage to thereby determine an output voltage signal representative of the output voltage;   summing said output current signal and said output voltage signal to thereby determine a voltage feedback signal;   comparing said voltage feedback signal with a reference voltage to thereby determine an error signal;   further comparing said error signal to a ramp voltage signal to thereby determine a current control signal; and   controlling the output voltage based at least in part upon said current control signal.   
     
     
       8. The method of  claim 7 , wherein said sensing step comprises sensing the output current with a current sensor, said current sensor issuing said output current signal. 
     
     
       9. The method of  claim 7 , wherein said summing step comprises a summing circuit configured for adding together said output current signal and said output voltage signal. 
     
     
       10. The method of  claim 7 , wherein said comparing step comprises an error amplifier having a summing input, each of said output current signal and said output voltage signal being electrically connected to said summing input, said error amplifier having a reference input electrically connected to a reference voltage supply, said error amplifier issuing an error signal representative of a difference between the sum of said output current signal and said output voltage signal and the reference voltage. 
     
     
       11. The method of  claim 7 , wherein said further comparing step comprises a comparator having a first input electrically connected to said error signal and a second input connected to a voltage ramp signal, said comparator comparing said error signal to said voltage ramp signal and issuing said current control signal. 
     
     
       12. The method of  claim 7 , wherein said controlling step comprises electrically connecting said current control signal to at least one power transistor, said power transistor configured for adjustably sourcing the output current in response to said current control signal. 
     
     
       13. A controller for a DC/DC converter having an output voltage and sourcing an output current to a load, the controller comprising:
 at least one first node adapted to receive a signal representative of the output current;   at least one second node adapted to receive a signal representative of the output voltage;   an error amplifier, responsive to the signal representative of the output current from the at least one first node and the signal representative of the output voltage from the at least one second node, and adapted to issue an error signal dependent at least in part upon the signal representative of the output voltage, the signal representative of the output current and a first reference signal; and   a comparator, responsive to the error amplifier, the comparator adapted to issue a comparator output signal, the comparator output signal based at least in part upon the error signal and a second reference signal.    
     
     
       14. The controller of claim 13, wherein the second reference signal comprises a ramp signal.  
     
     
       15. The controller of claim 13, further including a summer circuit coupled to one input of the error amplifier to combine at least two of the signal representative of the output voltage, the signal representative of the output current and the first reference signal.  
     
     
       16. A controller for a DC/DC converter having an output voltage and sourcing an output current to a load, the controller comprising:
 an error amplifier adapted to issue an error signal dependent at least in part upon a signal representative of the output voltage, a signal representative of the output current and a first reference signal;   a comparator, responsive to the error signal from the error amplifier, the comparator adapted to issue a comparator signal, the comparator signal based at least in part upon the error signal and a second reference signal; and   a summer circuit coupled to one input of the error amplifier to combine at least two of the signal representative of the output voltage, the signal representative of the output current and the first reference signal.    
     
     
       17. A controller for a DC/DC converter having an output voltage and sourcing an output current to a load, the controller comprising:
 at least one first node adapted to receive a signal representative of the output current;   at least one second node adapted to receive a signal representative of the output voltage;   an error amplifier, coupled to the at least one first node and the at least one second node, and adapted to issue an error output dependent at least in part upon the signal representative of the output voltage, the signal representative of the output current and a first reference; and   a comparator, coupled to the error amplifier, the comparator adapted to issue a comparator output, the comparator output based at least in part upon the error output and a second reference.    
     
     
       18. The controller of claim 17, wherein the second reference comprises a ramp signal.  
     
     
       19. The controller of claim 17, further including a summer circuit coupled to one input of the error amplifier to combine at least two of the signal representative of the output voltage, the signal representative of the output current and the first reference.  
     
     
       20. A controller for a DC/DC converter having an output voltage and sourcing an output current to a load, the controller comprising:
 at least one first node adapted to receive a signal representative of the output current;   at least one second node adapted to receive a signal representative of the output voltage;   an error amplifier, responsive to the signal representative of the output current from the at least one first node and the signal representative of the output voltage from the at least one second node, and adapted to issue an error signal dependent at least in part upon the signal representative of the output voltage, the signal representative of the output current and a first reference;   a comparator, responsive to the error amplifier, the comparator adapted to issue a comparator output signal, the comparator output signal based at least in part upon the error signal and a second reference; and   an output circuit, responsive to the comparator output signal, and adapted to provide a control signal based at least in part upon the comparator output signal that controls the DC/DC converter.    
     
     
       21. A controller for a DC/DC converter having an output voltage and sourcing an output current to a load, the controller comprising:
 an error amplifier adapted to issue an error signal dependent at least in part upon a signal representative of the output voltage, a signal representative of the output current and a first reference;   a comparator, responsive to the error signal from the error amplifier, the comparator adapted to issue a comparator signal, the comparator signal based at least in part upon the error signal and a second reference; and   an output circuit, responsive to the output signal from the comparator, and adapted to provide a control signal based at least in part upon the comparator signal, wherein the control signal controls the DC/DC converter.    
     
     
       22. The circuit of claim 17, wherein the error amplifier has a high bandwidth.