Switching converter having audible noise suppression and conversion control circuit and method thereof
A switching converter includes: a power stage circuit including at least one switch to switch an inductor to convert an input power to an output power; a modulation circuit executing a pulse width modulation according to a feedback signal related to the output power and a reference signal to generate a modulation trigger signal; a time calculation circuit generating a pulse width modulation (PWM) signal according to the modulation trigger signal to control the at least one switch and computing an ON-time or an OFF-time of the PWM signal; and a time adjustment circuit generating a time adjustment signal according to a first clock signal related to the PWM signal, wherein the time adjustment signal adjusts the ON-time or OFF-time in a random or a pseudo-random fashion, so as to suppress a noise resulting from a switching frequency of the PWM signal.
1 . A switching converter, which is configured to operably convert an input power to an output power; the switching converter comprising:
a power stage circuit including at least one switch, wherein the power stage circuit is configured to operably switch an inductor, to generate the output power;
a modulation circuit, which is configured to operably execute a pulse width modulation according to a feedback signal related to the output power and a reference signal, to generate a modulation trigger signal;
a time calculation circuit, which is configured to operably generate a pulse width modulation (PWM) signal according to the modulation trigger signal, and which is configured to operably calculate an ON-time or an OFF-time of the PWM signal, wherein the at least one switch is controlled to switch according to the PWM signal and according to a zero current signal generated by a zero current detector that detects a current related to the output power; and
a time adjustment circuit, which is configured to operably generate a time adjustment signal according to a first clock signal related to the PWM signal, wherein when the switching converter operates in a discontinuous conduction mode (DCM) and a switching frequency of the PWM signal is lower than a predetermined frequency threshold, the time adjustment signal is configured to operably adjust the ON-time or the OFF-time in a random or a pseudo-random fashion;
wherein when the switching converter operates in a continuous conduction mode (CCM), the switching frequency is kept as a constant.
2 . The switching converter of claim 1 , wherein the ON-time or the OFF-time, adjusted by the time adjustment signal, has a random characteristic or pseudo-random characteristic, such that the PWM signal has a spread spectrum characteristic.
3 . The switching converter of claim 2 , wherein the predetermined frequency threshold is smaller than or equal to 30 kHz and greater than or equal to 20 kHz.
4 . The switching converter of claim 2 , wherein the modulation trigger signal is configured to operably trigger the PWM signal to turn to a first state, wherein when the PWM signal is in the first state, the time calculation circuit is configured to operably execute an integration operation of a first current source via an integration capacitor, to generate a first integration voltage, and the time calculation circuit is configured to operably compare the first integration voltage with a reference voltage, to generate a first comparison signal, wherein when the first comparison signal indicates that the first integration voltage exceeds the reference voltage, the PWM signal turns to a second state.
5 . The switching converter of claim 4 , wherein the time adjustment signal is configured to operably adjust the first current source, a capacitance of the integration capacitor or a voltage level of the reference voltage in a random or a pseudo-random fashion, so as to adjust the ON-time or the OFF-time.
6 . The switching converter of claim 5 , wherein the first current source is proportional to the input power, whereas, the reference voltage is proportional to the output power, so that when the switching converter operates in a continuous conduction mode (CCM), the switching frequency is kept as a constant.
7 . The switching converter of claim 4 , wherein the time adjustment circuit includes:
a frequency detector, which is configured to operably generate a second comparison signal according to the first clock signal, wherein the second comparison signal indicates whether the switching frequency is lower than the predetermined frequency threshold during each switching period, wherein the switching period is a reciprocal of the switching frequency; and
a random number generator, which is configured to operably generate the time adjustment signal having a random characteristic or a pseudo-random characteristic according to the second comparison signal, to correspondingly adjust the ON-time or the OFF-time.
8 . The switching converter of claim 7 , wherein the random number generator includes a linear feedback shift register (LFSR), wherein a pulse of the second comparison signal triggers a shifting operation of the LFSR, to generate the time adjustment signal having the pseudo-random characteristic.
9 . The switching converter of claim 7 , wherein the random number generator includes:
a state circuit, which is configured to operably generate an enable signal according to the second comparison signal and the modulation trigger signal; and
a linear feedback shift register, which is configured to operably generate the time adjustment signal having the pseudo-random characteristic according to the enable signal and a second clock signal, wherein the second clock signal is correlated with the modulation trigger signal, the first comparison signal, the PWM signal or the second comparison signal.
10 . The switching converter of claim 7 , wherein the frequency detector is configured to operably execute an integration operation of a second current source via the first clock signal, to generate a second integration voltage, wherein when the second integration voltage exceeds a voltage threshold, the second comparison signal indicates that the switching frequency is lower than the predetermined frequency threshold.
11 . The switching converter of claim 1 , wherein the modulation circuit includes:
an error amplifier, which is configured to operably generate an error amplification signal according to the feedback signal and the reference signal; and
a PWM comparator, which is configured to operably compare a ramp signal with the error amplification signal, to generate the modulation trigger signal;
wherein the ramp signal is generated according to an output current of the output power.
12 . A conversion control circuit for use in a switching converter, wherein the switching converter includes at least one switch which is configured to operably switch an inductor, to convert an input power to an output power; the conversion control circuit comprising:
a modulation circuit, which is configured to operably execute a pulse width modulation according to a feedback signal related to the output power and a reference signal, to generate a modulation trigger signal;
a time calculation circuit, which is configured to operably generate a pulse width modulation (PWM) signal according to the modulation trigger signal, and which is configured to operably calculate an ON-time or an OFF-time of the PWM signal, wherein the at least one switch is controlled to switch according to the PWM signal and according to a zero current signal generated by a zero current detector that detects a current related to the output power; and
a time adjustment circuit, which is configured to operably generate a time adjustment signal according to a first clock signal related to the PWM signal, wherein when the switching converter operates in a discontinuous conduction mode (DCM) and a switching frequency of the PWM signal is lower than a predetermined frequency threshold, the time adjustment signal is configured to operably adjust the ON-time or the OFF-time in a random or a pseudo-random fashion;
wherein when the switching converter operates in a continuous conduction mode (CCM), the switching frequency is kept as a constant.
13 . The conversion control circuit of claim 12 , wherein the ON-time or the OFF-time, adjusted by the time adjustment signal, has a random characteristic or pseudo-random characteristic, such that the PWM signal has a spread spectrum characteristic.
14 . The conversion control circuit of claim 13 , wherein the predetermined frequency threshold is smaller than or equal to 30 kHz and greater than or equal to 20 kHz.
15 . The conversion control circuit of claim 13 , wherein the modulation trigger signal is configured to operably trigger the PWM signal to turn to a first state, wherein when the PWM signal is in the first state, the time calculation circuit is configured to operably execute an integration operation of a first current source via an integration capacitor, to generate a first integration voltage, and the time calculation circuit is configured to operably compare the first integration voltage with a reference voltage, to generate a first comparison signal, wherein when the first comparison signal indicates that the first integration voltage exceeds the reference voltage, the PWM signal turns to a second state.
16 . The conversion control circuit of claim 15 , wherein the time adjustment signal is configured to operably adjust the first source, current a capacitance of the integration capacitor or a voltage level of the reference voltage in a random or a pseudo-random fashion, so as to adjust the ON-time or the OFF-time.
17 . The conversion control circuit of claim 16 , wherein the first current source is proportional to the input power, whereas, the reference voltage is proportional to the output power, so that when the switching converter operates in a continuous conduction mode (CCM), the switching frequency is kept as a constant.
18 . The conversion control circuit of claim 15 , wherein the time adjustment circuit includes:
a frequency detector, which is configured to operably generate a second comparison signal according to the first clock signal, wherein the second comparison signal indicates whether the switching frequency is lower than the predetermined frequency threshold during each switching period, wherein the switching period is a reciprocal of the switching frequency; and
a random number generator, which is configured to operably generate the time adjustment signal having a random characteristic or a pseudo-random characteristic according to the second comparison signal, to correspondingly adjust the ON-time or the OFF-time.
19 . The conversion control circuit of claim 18 , wherein the random number generator includes a linear feedback shift register (LFSR), wherein a pulse of the second comparison signal triggers a shifting operation of the LFSR, to generate the time adjustment signal having the pseudo-random characteristic.
20 . The conversion control circuit of claim 18 , wherein the random number generator includes:
a state circuit, which is configured to operably generate an enable signal according to the second comparison signal and the modulation trigger signal; and
a linear feedback shift register, which is configured to operably generate the time adjustment signal having the pseudo-random characteristic according to the enable signal and a second clock signal, wherein the second clock signal is correlated with the modulation trigger signal, the first comparison signal, the PWM signal or the second comparison signal.
21 . The conversion control circuit of claim 18 , wherein the frequency detector is configured to operably execute an integration operation of a second current source according to a control by the first clock signal, to generate a second integration voltage, wherein when the second integration voltage exceeds a voltage threshold, the second comparison signal indicates that the switching frequency is lower than the predetermined frequency threshold.
22 . The conversion control circuit of claim 12 , wherein the modulation circuit includes:
an error amplifier, which is configured to operably generate an error amplification signal according to the feedback signal and the reference signal; and
a PWM comparator, which is configured to operably compare a ramp signal with the error amplification signal, to generate the modulation trigger signal;
wherein the ramp signal is generated according to an output current of the output power.
23 . A control method configured to control a switching converter, wherein the switching converter includes at least one switch, which is configured to operably switch an inductor, to convert an input power to an output power; the control method comprising following steps:
executing a pulse width modulation according to a feedback signal related to the output power and a reference signal, to generate a modulation trigger signal;
generating a pulse width modulation (PWM) signal according to the modulation trigger signal, and calculating an ON-time or an OFF-time of the PWM signal, wherein the at least one switch is controlled to switch according to the PWM signal and according to a zero current signal related to a current of the output power; and
generating a time adjustment signal according to a first clock signal related to the PWM signal, wherein when the switching converter operates in a discontinuous conduction mode (DCM) and a switching frequency of the PWM signal is lower than a predetermined frequency threshold, the time adjustment signal is configured to operably adjust the ON-time or OFF-time in a random or a pseudo-random fashion;
wherein when the switching converter operates in a continuous conduction mode (CCM), the switching frequency is kept as a constant.
24 . The control method of claim 23 , wherein the ON-time or the OFF-time, adjusted by the time adjustment signal, has a random characteristic or pseudo-random characteristic, such that the PWM signal has a spread spectrum characteristic.
25 . The control method of claim 24 , wherein the predetermined frequency threshold is smaller than or equal to 30 kHz and greater than or equal to 20 kHz.
26 . The control method of claim 24 , wherein the modulation trigger signal is configured to operably trigger the PWM signal to turn to a first state, and wherein the control method further comprises: when the PWM signal is in the first state, executing an integration operation of a first current source by an integration capacitor to generate a first integration voltage, and comparing the first integration voltage with a reference voltage to generate a first comparison signal, wherein when the first comparison signal indicates that the first integration voltage exceeds the reference voltage, the PWM signal turns to a second state;
wherein the time adjustment signal adjusts the first current source, a capacitance of the integration capacitor or a voltage level of the reference voltage in a random or a pseudo-random fashion, so as to adjust the ON-time or the OFF-time.
27 . The control method of claim 26 , wherein the first current source is proportional to the input power, and the reference voltage is proportional to the output power, so that when the switching converter operates in a continuous conduction mode (CCM), the switching frequency is kept as a constant.
28 . The control method of claim 26 , further comprising following steps:
generating a second comparison signal according to the first clock signal, wherein the second comparison signal indicates whether the switching frequency is lower than the predetermined frequency threshold during each switching period, wherein the switching period is a reciprocal of the switching frequency; and
generating the time adjustment signal having a random characteristic or a pseudo-random characteristic according to the second comparison signal, to correspondingly adjust the ON-time or the OFF-time.
29 . The control method of claim 28 , further comprising following steps:
generating an according enable signal to the second comparison signal and the modulation trigger signal; and
generating the time adjustment signal having the pseudo-random characteristic according to the enable signal and a second clock signal, wherein the second clock signal is correlated with the modulation trigger signal, the first comparison signal, the PWM signal or the second comparison signal.
30 . The control method of claim 28 , further comprising:
executing an integration operation of a second current source by a control of the first clock signal to generate a second integration voltage, wherein when the second integration voltage exceeds a voltage threshold, the second comparison signal indicates that the switching frequency is lower than the predetermined frequency threshold.