Current detection circuit, synchronous rectification type DC/DC buck converter and control circuit thereof
The present disclosure provides a current detecting circuit, a synchronous rectification type DC/DC buck converter and a control circuit thereof. The current detection circuit is used with a push-pull switching circuit to detect a source current flowing in a low-side transistor. The switching circuit, (i) in a first phase, connects a first end of the capacitor to a ground line, and connects a second end of the capacitor to a switch line connecting a high-side transistor and the low-side transistor. The switching circuit, (ii) in a second phase, sets the first end of the capacitor to a high impedance, and connects a second end of the capacitor to the ground line. An output circuit has a high impedance input and outputs a current detection signal based on a voltage generated at the first end of the capacitor in the second phase.
1. A control circuit for a synchronous rectifier including a high-side transistor and a low-side transistor, the control circuit comprising:
a current detection circuit, generating a current detection signal which indicates a current flowing through the low-side transistor while the low-side transistor is on; and
a pulse modulator that generates a pulse signal for controlling the high-side transistor and the low-side transistor based on the current detection signal, wherein the current detection circuit includes:
a capacitor;
a switch circuit,
(ii) in a first phase, connecting a first end of the capacitor to a ground line, and connecting a second end of the capacitor to a switch line to which the high-side transistor and the low-side transistor are connected, and
(ii) in a second phase, setting the first end of the capacitor to a high impedance, and connecting the second end of the capacitor to the ground line; and
An output circuit, having a high impedance input and outputting a current detection signal based on a voltage generated at the first end of the capacitor in the second phase.
2. The control circuit of claim 1 , wherein the switch circuit includes:
a first switch, disposed between the first end of the capacitor and the ground line, and being turned on in the first phase;
a second switch, disposed between the second end of the capacitor and the switching line, and being turned on in the first phase;
a third switch, disposed between the second end of the capacitor and the ground line, and being turned on in the second phase; and
a fourth switch, having an end connected to the first end of the capacitor, and being turned on in the second phase.
3. The control circuit of claim 2 , wherein the output circuit further includes a voltage/current conversion circuit that converts the voltage generated at the first end of the capacitor into a current signal in the second phase.
4. The control circuit of claim 3 , wherein the voltage/current conversion circuit includes:
a first transistor, having a first terminal connected to a power supply line;
a second transistor, having a first terminal connected to the power supply line, and including a control terminal connected to a control terminal of the first transistor;
a resistor, disposed between a second terminal of the first transistor and the ground line; and
an operational amplifier, receiving the voltage generated at the first end of the capacitor and a voltage at the second end of the first transistor, and having an output node connected to the control terminal of the first transistor, wherein
the voltage/current conversion circuit outputs a current flowing in the second transistor.
5. The control circuit of claim 2 , wherein the control circuit is integrated on a semiconductor substrate.
6. A synchronous rectification type DC/DC buck converter comprising the control circuit of claim 2 .
7. The control circuit of claim 1 , wherein the output circuit further includes a voltage/current conversion circuit that converts the voltage generated at the first end of the capacitor into a current signal in the second phase.
8. The control circuit of claim 7 , wherein the voltage/current conversion circuit includes:
a first transistor, having a first terminal connected to a power supply line;
a second transistor, having a first terminal connected to the power supply line, and including a control terminal connected to a control terminal of the first transistor;
a resistor, disposed between a second terminal of the first transistor and the ground line; and
an operational amplifier, receiving the voltage generated at the first end of the capacitor and a voltage at the second end of the first transistor, and having an output node connected to the control terminal of the first transistor, wherein
the voltage/current conversion circuit outputs a current flowing in the second transistor.
9. The control circuit of claim 1 , wherein the control circuit is integrated on a semiconductor substrate.
10. A synchronous rectification type DC/DC buck converter comprising the control circuit of claim 1 .
11. A current detection circuit, used with a push-pull switching circuit that includes a high-side transistor and a low-side transistor, and detecting a source current flowing through the low-side transistor, the current detection circuit comprising:
a capacitor;
a switch circuit,
(i) in a first phase, connecting a first end of the capacitor to a ground line, and connecting a second end of the capacitor to a switch line to which the high-side transistor and the low-side transistor are connected, and
(ii) in a second phase, setting the first end of the capacitor to a high impedance, and connecting the second end of the capacitor to the ground line; and
an output circuit, having a high impedance input and outputting a current detection signal based on a voltage generated at the first end of the capacitor in the second phase.
12. The current detection circuit of claim 11 , wherein the switch circuit includes:
a first switch, disposed between the first end of the capacitor and the ground line, and being turned on in the first phase;
a second switch, disposed between the second end of the capacitor and the switching line, and being turned on in the first phase;
a third switch, disposed between the second end of the capacitor and the ground line, and being turned on in the second phase; and
a fourth switch, having an end connected to the first end of the capacitor, and being turned on in the second phase.
13. The current detection circuit of claim 12 , wherein the output circuit further includes a voltage/current conversion circuit that converts the voltage generated at the first end of the capacitor into a current signal in the second phase.
14. The current detection circuit of claim 13 , wherein the voltage/current conversion circuit includes:
a first transistor, having a first terminal connected to a power supply line;
a second transistor, having a first terminal connected to the power supply line, and including a control terminal connected to a control terminal of the first transistor;
a resistor, disposed between a second terminal of the first transistor and the ground line; and
an operational amplifier, receiving the voltage generated at the first end of the capacitor and a voltage at the second end of the first transistor, and having an output node connected to the control terminal of the first transistor, wherein
the voltage/current conversion circuit outputs a current flowing in the second transistor.
15. The current detection circuit of claim 12 , wherein the current detection circuit is integrated on a semiconductor substrate.
16. The current detection circuit of claim 11 , wherein the output circuit further includes a voltage/current conversion circuit that converts the voltage generated at the first end of the capacitor into a current signal in the second phase.
17. The current detection circuit of claim 16 , wherein the voltage/current conversion circuit includes:
a first transistor, having a first terminal connected to a power supply line;
a second transistor, having a first terminal connected to the power supply line, and including a control terminal connected to a control terminal of the first transistor;
a resistor, disposed between a second terminal of the first transistor and the ground line; and
an operational amplifier, receiving the voltage generated at the first end of the capacitor and a voltage at the second end of the first transistor, and having an output node connected to the control terminal of the first transistor, wherein
the voltage/current conversion circuit outputs a current flowing in the second transistor.
18. The current detection circuit of claim 17 , wherein the current detection circuit is integrated on a semiconductor substrate.
19. The current detection circuit of claim 16 , wherein the current detection circuit is integrated on a semiconductor substrate.
20. The current detection circuit of claim 11 , wherein the current detection circuit is integrated on a semiconductor substrate.