Bandgap reference circuit and DCDC converter having the same
To provide a bandgap reference circuit capable of shortening a start time at power-on in a circuit lowered in power consumption. There is provided a bandgap reference circuit using an op amplifier to generate a reference voltage, which is equipped with a first current source connected between a power supply terminal and an operating current input terminal of the op amplifier, a second current source having one end connected to the power supply terminal, and a switch connected between the other end of the second current source and the operating current input terminal of the op amplifier, and in which a switch is turned on at power-on and turned off after starting of the reference voltage.
1. A DC-DC converter comprising:
a bandgap reference circuit comprising:
an op amplifier to control generation of a first reference voltage;
a first current source connected between a power supply terminal and an operating current input terminal of the op amplifier;
a second current source having one end connected to the power supply terminal;
a switch connected between the other end of the second current source and the operating current input terminal of the op amplifier; and
a control circuit which generates a control signal controlling on/off of the switch,
wherein the switch is turned on when the control signal is a first state and turned off when the control signal is a second state; and
an error amplifier coupled to the bandgap reference circuit, the error amplifier having an inversion input terminal inputted with a feedback voltage obtained by dividing an output voltage of the DC-DC converter, a non-inversion input terminal inputted with the first reference voltage from the bandgap reference circuit, and an output of the error amplifier controlling, at least in part, the operation of the DC-DC converter;
wherein the control circuit has a comparator which compares a third reference voltage and an output voltage of the output of the error amplifier, to be a reference of switching from a pulse-width modulation (PWM) operation of the DC-DC converter to a pulse-frequency modulation (PFM) operation of the DC-DC converter, and outputs the control signal as an output signal based on the comparison.
2. A DC-DC converter comprising:
a bandgap reference circuit comprising:
an op amplifier to control generation of a first reference voltage;
a first current source connected between a power supply terminal and an operating current input terminal of the op amplifier;
a second current source having one end connected to the power supply terminal;
a switch connected between the other end of the second current source and the operating current input terminal of the op amplifier; and
a control circuit which generates a control signal controlling on/off of the switch,
wherein the switch is turned on when the control signal is the first state and turned off when the control signal is the second state, and
wherein the control circuit brings the control signal into the first state at a time of a pulse-width modulation (PWM) operation of the DC-DC converter, and brings the control signal into the second state at a time of a pulse-frequency modulation (PFM) operation of the DC-DC converter; and
an error amplifier coupled to the bandgap reference circuit, the error amplifier having an inversion input terminal inputted with a feedback voltage obtained by dividing an output voltage of the DC-DC converter, a non-inversion input terminal inputted with the first reference voltage from the bandgap reference circuit, and an output of the error amplifier controlling, at least in part, the operation of the DC-DC converter in response to the feedback voltage,
wherein the control circuit has a comparator which compares a third reference voltage and an output voltage of the output of the error amplifier, to be a reference of switching from the PWM operation to the PFM operation, and outputs the control signal as an output signal.
3. The DC-DC converter according to claim 2 ,
wherein the comparator brings the control signal into the first state when the output voltage of the output of the error amplifier is higher than the third reference voltage, and brings the control signal into the second state when the output voltage of the output of the error amplifier is lower than the third reference voltage.
4. A bandgap reference circuit comprising:
an op amplifier to control generation of a first reference voltage;
a first current source connected between a power supply terminal and an operating current input terminal of the op amplifier;
a second current source having one end connected to the power supply terminal;
a switch connected between the other end of the second current source and the operating current input terminal of the op amplifier; and
a control circuit configured to change a control signal generated by the control circuit from a first state to a second state,
wherein the control signal controls the switch to turn the switch on when the control signal is the first state and to turn the switch off when the control signal is the second state,
wherein the control circuit has a comparator which compares a third reference voltage and an output voltage of the output of the error amplifier, to be a reference of switching from a pulse-width modulation (PWM) operation of the DC-DC converter to a pulse-frequency modulation (PFM) operation of the DC-DC converter, and outputs the control signal as an output signal based on the comparison.
5. A DC-DC converter comprising:
the bandgap reference circuit according to claim 4 ; and
an error amplifier coupled to the bandgap reference circuit, the error amplifier having an inversion input terminal inputted with a feedback voltage obtained by dividing an output voltage of the DC-DC converter, and a non-inversion input terminal inputted with the first reference voltage from the bandgap reference circuit, and an output of the error amplifier controlling, at least in part, the operation of the DC-DC converter.