Adaptive off-time or on-time DC-DC converter
A converter system includes a first switch and a controller configured to switch the first switch between first and second states based on input and output voltages of the converter system. The controller includes: a timer unit including a first timer configured to determine a first duration based on a target switching frequency of the converter system; and a second timer configured to determine a second duration based on a predetermined duration equal to or greater than a minimum duration of the first state of the first switch and the input and output voltages; and a control logic unit configured to switch the first switch from the second state to the first state responsive to expiration of both the first and second durations.
1. A DC-DC converter system, comprising:
a first switch coupled to a switching terminal of the DC-DC converter system, and configured to operate between first and second states;
a first timer comprising:
a first capacitive element with a first capacitance;
a first timer switch coupled in parallel with the first capacitive element;
a first current source coupled in series with the first capacitive element and configured to source or sink a first current to or from the first capacitive element; and
a first comparator with a first input terminal coupled to the first capacitive element, a second input terminal configured to receive a first reference voltage, and an output terminal configured to generate a first timer expired signal responsive to expiration of a first duration determined in response to the first capacitance, the first current source and the first reference voltage;
a second timer comprising:
a second capacitive element with a second capacitance;
a second timer switch coupled in parallel with the second capacitive element;
a second current source coupled in series with the second capacitive element and configured to source or sink a second current to or from the second capacitive element; and
a second comparator with a first input terminal coupled to the second capacitive element, a second input terminal configured to receive a second reference voltage, and an output terminal configured to generate a second timer expired signal responsive to expiration of a second duration determined in response to the second capacitance, the second current source and the second reference voltage;
a logic gate coupled to outputs of the first and second comparators, and configured to generate an expiration signal in response to expiration of both the first and second timers; and
a control logic unit, coupled between the logic gate and a control terminal of the first switch, configured to switch the first switch from the second state to the first state in response to the expiration signal, wherein:
the first timing switch is coupled to the control logic unit, and is configured to be switched off in response to the first switch being switched from the first state to the second state; and
the second timer switch is coupled to the control logic unit, and is configured to be switched off with the first timing switch.
2. The DC-DC converter system of claim 1 , wherein:
the first comparator is configured to generate the first timer expired signal responsive to a voltage difference across the first capacitive element changing by a first voltage difference, wherein the first duration is determined by a target switch cycle and input and output voltages of the DC-DC converter system,
and
the second comparator is configured to generate the second timer expired signal responsive to a voltage difference across the second capacitive element changing by a second voltage difference, wherein the second duration is determined by a predetermined duration equal to or greater than a minimum duration of the first state of the first switch and the input and output voltages of the DC-DC converter system.
3. The DC-DC converter system of claim 2 , wherein:
a product of the first capacitance and a ratio of the first voltage difference to the first current equals to a duration of the second state of the first switch determined by the target switch cycle and input and output voltages of the DC-DC converter system, and
a product of the second capacitance and a ratio of the second voltage difference to the second current equals to an adjusted duration of the second state of the first switch determined by the predetermined duration and the input and output voltages of the DC-DC converter system.
4. The DC-DC converter system of claim 1 , further comprising:
a one-shot signal generator configured to generate a one-shot signal in response to the first switch being switched from the second state to the first state, wherein
the first timing switch includes a control terminal coupled to receive the one-shot signal, and is configured to be switched off when the one-shot signal is de-asserted,
the first comparator is configured to generate the first timer expired signal responsive to a voltage difference across the first capacitive element changing by a first voltage difference, wherein the first duration is determined by a target switch cycle of the DC-DC converter system,
the second timing switch includes a control terminal coupled to receive the one-shot signal, and is configured to be switched off substantially simultaneously with the first timing switch, and
the second comparator is configured to generate the second timer expired signal responsive to a voltage difference across the second capacitive element changing by a second voltage difference, wherein the second duration is determined by a predetermined duration substantially equal to or longer than a minimum duration of the first state of the first switch and input and output voltages of the DC-DC converter system.
5. The DC-DC converter system of claim 4 , wherein:
a product of the first capacitance and a ratio of the first voltage difference to the first current equals to a target switch cycle of the DC-DC converter system, and
a product of the second capacitance and a ratio of the second voltage difference to the second current equals to an adjusted switch cycle of the DC-DC converter system determined by the predetermined duration and the input and output voltages of the DC-DC converter system.
6. A system comprising:
a first timer configured to generate a first timer expired signal in response to a first duration time;
a second timer configured to generate a second timer expired signal in response to a second duration time;
a logic circuit configured to generate an expiration signal in response to the first timer expired signal and the second timer expired signal; and
a control circuit configured to switch a switch from a second state to a first state in response to the expiration signal, wherein:
the first timer is configured to start timing of the first duration time with the second timer starting timing of the second duration time in response to the switch being switched from the first state to the second state; and
the system is capable of a target switching frequency determined by a capacitance and a resistance of a charging path in the first timer, and the first duration time is based on the target switching frequency of the system and an input voltage and an output voltage.
7. The system of claim 6 , wherein:
the second duration time is determined by a minimum off time of a second switch, the input voltage, and the output voltage.
8. The system of claim 6 , wherein:
in response to the first timer expired signal and the second timer expired signal being asserted, the expiration signal is generated by the logic circuit.
9. The system of claim 6 , wherein:
the logic circuit is an AND gate.
10. The system of claim 6 , wherein:
the first timer includes a first timer switch coupled in parallel with a first capacitor; and
the second timer includes a second timer switch coupled in parallel with a second capacitor.
11. The system of claim 10 , wherein:
the first timer includes a first comparator with a first input terminal of the first timer coupled to the first capacitor, a second input terminal coupled to a first reference voltage; and
the second timer includes a second comparator with a first input terminal of the second timer coupled to the second capacitor, a second input terminal coupled to a second reference voltage.
12. The system of claim 11 , wherein:
the first input terminal of the first timer is coupled to a first current source; and
the first input terminal of the second timer is coupled to a second current source.
13. The system of claim 12 , wherein:
the first current source is generated by an input voltage to the system; and
the second current source is generated by an output voltage of the system.
14. The system of claim 6 , wherein:
the control circuit is configured to receive a control signal; and
the control signal is determined by a current in the switch.
15. The system of claim 14 , wherein:
the control signal is asserted in response to a sensing voltage associated with the switch reaches a control voltage threshold.
16. The system of claim 14 , wherein:
the control circuit is configured to turn off the switch in response to the control signal.
17. The system of claim 6 , wherein:
the control circuit is coupled to a driver circuit; and
the driver circuit is coupled to a control terminal of the switch.