Digital control switching power supply unit

1. A digital control switching power supply unit that converts an input voltage into a desired output voltage using a pulse width modulation signal, comprising:

an analog-to-digital converter circuit that includes:

a delay line circuit that has a first delay element array wherein delay elements whose delay times are controlled by a bias current are connected in series, and that converts a current value of the bias current flowing through the delay elements of the first delay element array into a digital value using a delay time of a start signal transmitted through the first delay element array;

a phase difference detector circuit that detects a phase difference between a switching cycle fixed by the pulse width modulation signal and a cycle of an analog-to-digital conversion wherein the delay line circuit converts the current value of the bias current into the digital value;

a charge pump circuit that generates a bias control voltage for generating the bias current in accordance with an output of the phase difference detector circuit; and

a bias current indicator circuit that determines the bias current based on an output of the charge pump circuit, and on a result of a comparison of a detected value of the output voltage and a reference voltage.

2. The digital control switching power supply unit according to claim 1 , wherein

the delay line circuit includes:

a first delay cell array that has the first delay element array wherein delay elements through which a delay output current flows as the bias current, and whose delay times are controlled by the delay output current, are connected in series, and a memory circuit that stores an output of the delay elements configuring the first delay element array using a timing signal;

a second delay cell array that has a second delay element array wherein delay elements through which a delay reference current flows as the bias current, and whose delay times are controlled by the delay reference current, are connected in series, and that generates the timing signal and a signal indicating the conversion cycle; and

an encoder circuit that encodes an output of the memory circuit.

3. The digital control switching power supply unit according to claim 1 , wherein

the phase difference detector circuit includes:

a circuit that, with the switching cycle as a reference, detects a difference in phase with that of the conversion cycle, and outputs an Up signal for a period in which there is a phase difference when the phase of the switching cycle is earlier; and

a circuit that, with the switching cycle as a reference, detects a difference in phase with that of the analog-to-digital conversion cycle, and outputs a Dwn signal for a period in which there is a phase difference when the phase of the switching cycle is later.

4. The digital control switching power supply unit according to claim 3 , wherein

the charge pump circuit includes:

a charging circuit that generates a charge current by copying a reference current, and charges a charge pump capacitor with the charge current for the period for which the Up signal is being output;

a discharging circuit that generates a discharge current by copying the reference current, and discharges the charge pump capacitor with the discharge current for the period for which the Dwn signal is being output; and

an output circuit that outputs the bias control voltage in accordance with a charge/discharge voltage of the charge pump capacitor.

5. The digital control switching power supply unit according to claim 1 , wherein

the bias current indicator circuit includes:

a constant current circuit that generates a constant current in accordance with the bias control voltage;

a first differential circuit that, with a current wherein the constant current is copied as an operating current and with the detected value of the output voltage and the reference voltage as inputs, outputs a signal determining the delay output current; and

a second differential circuit that, with a current wherein the constant current is copied as an operating current and with signals of the same potential as two inputs, outputs a signal determining the delay reference current.

6. A digital control switching power supply method that converts an input voltage into a desired output voltage using a pulse width modulation signal, comprising:

an analog-to-digital converter step that includes:

a delay line step that converts a current value of a bias current flowing through delay elements of a first delay element array into a digital value using a delay time of a start signal transmitted through the first delay element array;

a phase difference detector step that detects a phase difference between a switching cycle fixed by the pulse width modulation signal and a cycle of an analog-to-digital conversion wherein the delay line step converts the current value of the bias current into the digital value;

a charge pump step that generates a bias control voltage for generating the bias current in accordance with an output of the phase difference detector step; and

a bias current indicator step that determines the bias current based on an output of the charge pump step, and on a result of a comparison of a detected value of the output voltage and a reference voltage.

7. The digital control switching power supply method according to claim 6 , wherein

the phase difference detector step includes:

a step that, with the switching cycle as a reference, detects a difference in phase with that of the conversion cycle, and outputs an Up signal for a period in which there is a phase difference when the phase of the switching cycle is earlier; and

a step that, with the switching cycle as a reference, detects a difference in phase with that of the analog-to-digital conversion cycle, and outputs a Dwn signal for a period in which there is a phase difference when the phase of the switching cycle is later.

8. The digital control switching power supply method according to claim 7 , wherein

the charge pump step includes:

a charging step that generates a charge current by copying a reference current, and charges a charge pump capacitor with the charge current for the period for which the Up signal is being output;

a discharging step that generates a discharge current by copying the reference current, and discharges the charge pump capacitor with the discharge current for the period for which the Dwn signal is being output; and

an output step that outputs the bias control voltage in accordance with a charge/discharge voltage of the charge pump capacitor.