Automatic external switch detection in synchronous switching regulator controller
View Patent ↗A synchronous switching regulator controller incorporates a switch detection circuit to determine the presence or absence of a power switch at the output of a switch driver so that the switch driver can be disabled when it is left unused. In one embodiment, the synchronous controller includes a switch detection circuit receiving a power cycle signal and the PWM ramp clock signal and measuring a voltage at an output node of the switch driver. The switch detection circuit provides a driver enable signal in response to the assertion of the power cycle signal. The driver enable signal has a first logical state when the voltage at the output node of the switch driver is greater than a reference voltage and a second logical state when the voltage at the output node is less than a reference voltage. The switch driver can be disabled based on the driver enable signal.
1. A synchronous switching regulator controller comprising a first switch driver coupled to a first terminal to provide a first driving signal, a second switch driver coupled to a second terminal to provide a second driving signal, a PWM ramp clock generator providing a PWM ramp clock signal to a PWM comparator and a control logic circuit generating control signals for the first and second switch drivers based at least in part on the output signal of the PWM comparator, the synchronous switching regulator controller comprising:
a switch detection circuit receiving a power cycle signal indicating that the synchronous switching regulator controller is to be turned on and the PWM ramp clock signal, the switch detection circuit measuring a voltage at an output node of the second switch driver, the switch detection circuit providing a driver enable signal to the control logic circuit in response to the assertion of the power cycle signal, the driver enable signal having a first logical state when the voltage at the output node of the second switch driver is greater than a reference voltage and a second logical state when the voltage at the output node of the second switch driver is less than the reference voltage,
wherein the control logic circuit disables the second switch driver when the drive enable signal has the first logical state and enables the second switch driver when the drive enable signal has the second logical state.
2. The synchronous switching regulator controller of claim 1 , wherein the switch detection circuit comprises:
an one-shot circuit coupled to receive the power cycle signal and the PWM ramp clock signal, the one-shot circuit generating an one-shot pulse in response to the assertion of the power cycle signal, the one-shot pulse being synchronized to a first PWM pulse of the PWM ramp clock signal generated for the second switch driver;
a comparator having a first input terminal coupled to receive the voltage at the output node of the second switch driver, a second input terminal coupled to receive the reference voltage and an output terminal providing an output signal indicative of the difference between the voltage at the output node of the second switch driver and the reference voltage, the output signal of the comparator having a first logical state when the voltage at the output node is greater than the reference voltage and a second logical state when the voltage at the output node is less than the reference voltage; and
a latch having an enable terminal coupled to receive the one-shot pulse, a data terminal coupled to receive the output signal of the comparator, and an output terminal providing the driver enable signal, the latch operative to latch the output signal of the comparator at the falling edge of the one-shot pulse,
wherein the latch provides the driven enable signal having the same logical state as the output signal of the comparator at the falling edge of the one-shot pulse.
3. The synchronous switching regulator controller of claim 1 , wherein the driver enable signal has the first state to indicate that no power switch is connected to the second switch driver and the driver enable signal has the second state to indicate that a power switch is connected to the second switch driver.
4. The synchronous switching regulator controller of claim 1 , wherein the power cycle signal comprises an enable signal provided to the synchronous switching regulator controller.
5. The synchronous switching regulator controller of claim 1 , wherein the synchronous switching regulator controller is configured for converting a DC input voltage to a DC output voltage, the power cycle signal comprising a signal indicative of the DC input voltage having a value exceeding a threshold level.
6. The synchronous switching regulator controller of claim 2 , wherein the one-shot pulse has a pulse duration the same as or less than the pulse duration of the first PWM pulse of the PWM ramp clock signal.
7. The synchronous switching regulator controller of claim 2 , wherein the voltage at the output node of the second switch driver is greater than the reference voltage when the impedance at the output node is an open circuit.
8. The synchronous switching regulator controller of claim 2 , wherein the voltage at the output node of the second switch driver is less than the reference voltage when the impedance at the output node has a value associated with the input impedance of a power switch.
9. The synchronous switching regulator controller of claim 1 , wherein the reference voltage is generated internally in the synchronous switching regulator controller.
10. The synchronous switching regulator controller of claim 1 , wherein the reference voltage is an external voltage provided to the synchronous switching regulator controller.