Buck converter having improved transient response to load step down
View Patent ↗A synchronous buck converter having an improved transient response during output current includes a first switching transistor connected between an input node and a first node, a second switching transistor connected between the first node and a second node, a series inductor connected between the first node and an output node, an output capacitor connected between the output node and the second node, a first driver circuit operative to turn the first switching transistor one and off according to a variable duty cycle determined by an error signal representing the difference between the voltage output of the converter and a reference voltage, a sensing circuit operative to provide a control signal output when the duty cycle for the first switching transistor is zero, a second drive circuit responsive to the control signal output of the sensing circuit to turn off the second switching transistor and a second sensing circuit operative to provide a second control signal when a dissipating current of the inductor is zero, wherein the second drive circuit is responsive to the second control signal to turn the second switching transistor on when the dissipating current of the inductor is zero.
1. A synchronous buck converter having an improved transient response during the output current step down comprising:
a first switching transistor connected between an input node and a first node;
a second switching transistor connected between the first node and a second node;
a series inductor connected between the first node and an output node;
an output capacitor connected between the output node and the second node;
a first driver circuit operative to turn the first switching transistor on and off according to a variable duty cycle determined by an error signal representing the difference between the voltage output of the converter and a reference voltage;
a sensing circuit operative to provide a control signal output when the duty cycle for the first switching transistor is zero;
a second drive circuit responsive to the control signal output of the sensing circuit to turn off the second switching transistor; and
a second sensing circuit operative to provide a second control signal when a dissipating current of the inductor is zero, wherein the second drive circuit is responsive to the second control signal to turn the second switching transistor on when the dissipating current of the inductor is zero with said inductor connected to said output node, thereby enabling a reverse current to flow from the inductor through the second switching transistor and providing enhanced reduction of said voltage output at said output node.
2. The synchronous buck convener of claim 1 , wherein the second sensing circuit is operative to change the second control signal to turn the second switching circuit off when the output voltage reaches a desired value.
3. The synchronous buck converter of claim 1 , wherein:
said first switching transistor is a series MOSFET connected between the input node and the first node; and
said second switching transistor is a shunt MOSFET connected between the first node and the a second node.
4. The synchronous buck converter of claim 3 , wherein the second sensing circuit is operative to change the second control signal to turn the shunt MOSFET off when the output voltage reaches a desired value.