DC-DC converters operable in a discontinuous switching mode

• US 9,300,212 B2
• Filed: 07/29/2013
• Issued: 03/29/2016
• Est. Priority Date: 07/22/2009
• Status: Active Grant

• Current Assignee: Cirrus Logic Incorporated
• Original Assignee: Cirrus Logic International Semiconductor Ltd. (Cirrus Logic Incorporated)
• Inventors: Notman, Andrew, McCloy-Stevens, Mark, MacFarlane, Douglas James Wallace, Haiplik, Holger
• Primary Examiner(s): Finch, III, Fred E
• Application Number:
  US13/953,317
• Publication Number:
  US 20130314062A1
• Time in Patent Office: 974 Days
• US Class Current: 1/1
• CPC Class Codes: H02M 1/0009 Devices or circuits for detecting current in a converter
• CPC Class Codes: H02M 1/0032 Control circuits allowing low power mode operation, e.g. in standby mode
• CPC Class Codes: H02M 1/38 Means for preventing simultaneous conduction of switches
• CPC Class Codes: H02M 3/1588 comprising at least one synchronous rectifier element H02M3/1582, H02M3/1584 take precedence
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

Methods and apparatus for control of DC-DC converters, especially in valley current mode. The DC-DC converter is operable so that a low side supply switch may be turned off, before the high side supply switch is turned on. During the period when both switches are off the current loop control remains active and the change in inductor (L) current is emulated. One embodiment uses a current sensor for lossless current sensing and emulates the change in inductor current by holding the value of the output of the current sensor (ISNS) at the time that the low side switch turns off and adding an emulated ramp signal (VISLP) until the inductor current reaches zero. Embodiment employing a pulse-skip mode of operation based on a minimum conduction time are also disclosed. The invention enables a seamless transition from Continuous Conduction Mode the Discontinuous Conduction Mode and Pulse Skipping and provide converters that are efficient at low current loads.

Claims

1. DC-DC converter circuitry comprising:

a first node and an output node for connection to an inductor;

a high side switch operably connected between a high side supply input node and the first node;

a low side switch operably connected between a low side supply input node and the first node; and

switch control circuitry being;

configured to control the turn-on of said high side switch based on a comparison of at least a first signal indicative of the current flow in the inductor with a second signal indicative of a difference between the voltage at the output node and a target voltage; and

operable to prevent turning the high side switch on in a cycle if the period between turning the high side switch on and turning the high side switch off would be less than a first time period,

wherein the switch control circuitry comprises a first timer circuit configured to produce a first inhibit signal for a time period substantially equal to the first time period, before a clock edge which would cause the high side switch to turn off, wherein the high side switch is inhibited from turning-on when the first inhibit signal is being produced.

2. DC-DC converter circuitry as claimed in claim 1 wherein the first timer circuit comprises an input for receiving an input clock signal, a delay for producing a delayed clock signal and circuitry for generating the first inhibit signal based on the input clock signal.

3. DC-DC converter circuitry as claimed in claim 2 wherein the delay imparts a delay equal to the first time period and the delayed clock signal is used to control turn-off of the high-side switch.

4. DC-DC converter circuitry as claimed in claim 1 wherein the switch control circuitry comprises current sense circuitry for determining the current flow in the inductor from the electrical properties of the low side switch when the low side switch is turned on and wherein the output of said current sense circuit comprises the first signal when the low side switch is turned on.

5. DC-DC converter circuitry as claimed in claim 4 wherein the electrical properties of the low side switch comprise a source-drain voltage of a transistor.

6. DC-DC converter circuitry as claimed in claim 1 wherein the converter circuitry is configured to operate at a constant cycle frequency.

7. DC-DC converter circuitry as claimed in claim 1 comprising said inductor connected between said first node and said output node.

8. A power management integrated circuit comprising DC-DC converter circuitry as claimed in claim 1.

9. An electronic device comprising a DC-DC converter circuitry as claimed in claim 1.

10. An electronic device as claimed in claim 9 wherein the device is one of:

a portable computing device;

a laptop computer;

a personal data assistant;

a personal media player;

an mp3 player;

a portable television;

a mobile communications device;

a mobile telephone;

a navigation aid;

a GPS device;

a game console.

11. A method of controlling a DC-DC converter comprising an inductor operably connected between a first node and an output node;

a high side switch operably connected between a high side supply input node and the first node; and

a low side switch operably connected between a low side supply input node and the first node;

the method comprising;

controlling the turn on of said high side switch based on a comparison of at least a first signal indicative of the current flow in the inductor with a second signal indicative of a difference between the voltage at the output node and a target voltage; and

preventing turn-on of the high side switch in a cycle if the period between turning the high side switch on and turning the high side switch off would be less than a first time period;

wherein a first timer circuit produces a first inhibit signal for a time period substantially equal to the first time period, before a clock edge which would cause the high side switch to turn off, and wherein the high side switch is inhibited from turning-on when the first inhibit signal is being produced.

12. DC-DC converter circuitry comprising:

a high-side switch;

a low-side switch; and

switch control circuitry configured to switch said high-side switch and said low-side side switch in a valley current mode of operation with a switching cycle defined by a first clock signal,

wherein the switch control circuitry is configured to prevent turn-on of the high side switch within a first time period before the start of the next switching cycle; and

wherein the switching circuitry is configured to receive an input clock signal and produce a delayed clock signal, which is delayed with respect to the input clock signal by an amount equal to the first time period, wherein the delayed clock signal is used as the first clock signal and switch control circuitry prevents the high-side switch from being turned-on in a period defined by the input clock signal and the delayed clock signal.

13. DC-DC converter circuitry as claimed in claim 12 wherein the switch control circuitry asserts an inhibit signal between a clock edge of the input clock signal and the corresponding clock edge in the delayed clock signal that indicates the start of the next switching cycle, wherein the hide-side switch is prevented from being turned-on when the inhibit signal is asserted.