System and method for current limiting a DC-DC converter
A DC-DC voltage converter has a pair of switching transistors to provide an output voltage and are alternately switched in a boost mode of operation responsive to control signals. An inductor is connected to the pair of switching transistor and has an inductor current flowing there through. A current sensor monitors an input current and generates a current sense signal responsive thereto. Control circuitry generates the control signals to the second pair of switching transistors responsive to the current sense signal, the output voltage and a current limit signal, wherein when the current limit signal indicates the inductor current exceeds a current limit the control signals configure the pair of switching transistors to decrease the inductor current.
1. A DC-DC voltage converter, comprising:
a pair of switching transistor providing an output voltage that are alternately switched in a boost mode of operation responsive to control signals;
an inductor connected with the pair of switching transistor having an inductor current flowing therethrough;
a current sensor connected to monitor an input current;
control circuitry for generating the control signals to the pair of switching transistors responsive to the current sense signal, the output voltage and a current limit signal, wherein when the current limit signal indicates the inductor current exceeds a current limit the control signals configure the pair of switching transistors to decrease the inductor current, wherein the control circuitry further comprises:
driver circuitry for generating the control signals responsive to a PWM signal;
an error amplifier for comparing the output voltage with a reference voltage and generating an error voltage responsive thereto;
a PWM comparator for comparing the error voltage with a voltage signal responsive to the current sense signal;
an OR gate connected to the output of the PWM comparator and the current limit signal;
an inverter connected to the output of the OR gate; and
a latch connected to receive an output of the inverter and a clock signal and generating the PWM signal responsive thereto.
2. The DC-DC voltage converter of claim 1 further including a summation circuit for summing the current sense signal with an offset signal and a slope compensation signal to generate the voltage signal responsive to the current sense signal.
3. The DC-DC voltage converter of claim 1 further including a resistor divider connected to monitor the output voltage and providing an input to the error amplifier.
4. The DC-DC voltage converter of claim 1 , wherein the current limit signal replaces the output of the PWM comparator when the current limit signal is at a logical high level.
5. The DC-DC voltage converter of claim 1 , wherein the control circuitry generates the control signals to the pair of switching transistors in the boost mode of operation.
6. A DC-DC voltage converter, comprising:
a pair of switching transistor providing an output voltage that are alternately switched in a boost mode of operation responsive to control signals;
an inductor connected with the pair of switching transistor having an inductor current flowing therethrough;
a current sensor connected to monitor an input current;
control circuitry for generating the control signals to the pair of switching transistors responsive to the current sense signal, the output voltage and a current limit signal, wherein when the current limit signal indicates the inductor current exceeds a current limit the control signals configure the pair of switching transistors to decrease the inductor current, wherein the control circuitry further comprises:
driver circuitry for generating the control signals;
an error amplifier for comparing the output voltage with a reference voltage and generating an error voltage responsive thereto;
a PWM comparator for comparing the error voltage with a voltage signal responsive to the current sense signal;
an OR gate connected to the output of the PWM comparator and the current limit signal; and
an inverter connected to the output of the OR gate and providing an output to the driver circuitry.
7. The DC-DC voltage converter of claim 6 further including a summation circuit for summing the current sense signal with an offset signal and a slope compensation signal to generate the voltage signal responsive to the current sense signal.
8. The DC-DC voltage converter of claim 6 further including a resistor divider connected to monitor the output voltage and providing an input to the error amplifier.
9. The DC-DC voltage converter of claim 6 , wherein the current limit signal replaces the output of the PWM comparator when the current limit signal is at a logical high level.
10. The DC-DC voltage converter of claim 6 , wherein the control circuitry generates the control signals to the second pair of switching transistors in the boost mode of operation.
11. The DC-DC voltage converter of claim 6 , wherein the driver circuitry further comprises:
boost mode control logic for generating the control signals responsive to a PWM signal; and
a latch connected to receive an output of the inverter and a clock signal and generating the PWM signal responsive thereto.
12. A method for controlling operation of DC-DC voltage converter in a boost mode of operation, comprising the steps of:
receiving an input voltage;
alternately switching a pair of switching transistors in a boost mode of operation responsive to control signals;
generating a current sense signal responsive to the input current;
receiving a current limit signal indicating whether an inductor current through an inductor connected to the pair of transistors exceeds a predetermined level; and
generating the control signals to the pair of switching transistors responsive to the current sense signal, an output voltage and the current limit signal, wherein when the current limit signal indicates the inductor current exceeds a current limit the control signals configure the pair of switching transistors to decrease the inductor current, wherein the step of generating the control signals further comprises the steps of:
generating an error voltage responsive to a comparison between the output voltage and a reference voltage;
generating a PWM signal responsive to the error voltage with a voltage signal responsive to the current sense signal;
ORing the PWM signal with the current limit signal to generate a first control signal;
inverting the first control signal;
generating the control signals responsive to the inverted first control signal and a clock signal.
13. The method of claim 12 further including the step of summing the current sense signal with an offset signal and a slope compensation signal to generate the current sense responsive to the current sense signal.
14. The method of claim 12 further including the steps of:
monitoring the output voltage using a resistor divider; and
providing the monitored output voltage to an input to the error amplifier.
15. The method of claim 12 further including the step of replacing the output of the PWM comparator with the current limit signal when the current limit signal is at a logical high level.
16. The method of claim 12 , wherein the step of generating the control signals further comprises the step of generating the control signals to the second pair of switching transistors in the boost mode of operation.