Mutual blanking for a multi-channel converter

The present invention is related generally to a switching converter and, more particularly, to an apparatus and method for blanking switching noise in a switching converter.

In a switching converter, the switching elements generate large power bounce, ground bounce and switching noise when the switching elements turn on and turn off. The switching noise is mixed with signals through power lines and substrate and some common block, for example bandgap reference generator and comparator. If switching noise is superimposed on an analog signal that represents a sensing signal and the signal is sensed in this load state, the controller will be fault function. The fault function could be that the switching elements of other power switching converters turn on and turn off at the wrong timing.

FIG. 1 shows a conventional multi-channel switching converter 100 including several channels 106 , 108 , . . . , 110 . In the first channel 106 , transistors MH 1 and ML 1 are serially connected between a power line VIN and a ground line or substrate GND, a driver 116 generates signals U 1 and L 1 according to a pulse-width modulation (PWM) signal PWM 1 to switch the transistors MH 1 and ML 1 so as to generate an output voltage VOUT 1 , voltage divider resistors R 1 and R 2 divide the output voltage VOUT 1 to generate a feedback signal FB 1 , a current sensor 118 detects the current flowing through the transistor MH 1 to generate a current-sensing signal ISENSE 1 , and a controller 114 generates the pulse-width modulation signal PWM 1 according to the feedback signal FB 1 and the current-sensing signal ISENSE 1 . In the second channel 108 , transistors MH 2 and ML 2 are serially connected between the power line VIN and the ground line or substrate GND, a driver 122 generates signals U 2 and L 2 according to a pulse-width modulation signal PWM 2 to switch the transistors MH 2 and ML 2 so as to generate an output voltage VOUT 2 , voltage divider resistors R 3 and R 4 divide the output voltage VOUT 2 to generate a feedback signal FB 2 , a current sensor 124 detects the current flowing through the transistor MH 2 to generate a current-sensing signal ISENSE 2 , and a controller 120 generates the pulse-width modulation signal PWM 2 according to the feedback signal FB 2 and the current-sensing signal ISENSE 2 . In the N-th channel 110 , transistors MHN and MLN are serially connected between the power line VIN and the ground line GND, a driver 128 generates signals UN and LN according to a pulse-width modulation signal PWMN to switch the transistors MHN and MLN so as to generate an output voltage VOUTN, voltage divider resistors R 5 and R 6 divide the output voltage VOUTN to generate a feedback signal FBN, a current sensor 130 detects the current flowing through the transistor MHN to generate a current-sensing signal ISENSEN, and a controller 126 generates the pulse-width modulation signal PWMN according to the feedback signal FBN and the current-sensing signal ISENSEN.

In the converter 100 , the multiple channels 106 , 108 , . . . , 110 are integrated in a single chip 102 and all the channels 106 , 108 , . . . , 110 share the common power line VIN as well as the ground line or substrate GND. Package inductances Lp 1 , Lp 2 , . . . , LpN are resulted from bouning wires, and package inductances Lg 1 , Lg 2 , . . . , LgN are resulted from bouning wires between the ground line GND and the transistors ML 1 , ML 2 , . . . , MLN, respectively. Due to the switching of the transistors MH 1 , ML 1 , MH 2 , ML 2 , . . . , MHN, MLN in the channels 106 , 108 , . . . , 110 , power bounce and ground bounce are produced and mutually interfere each other therebetween through the common power line VIN as well as the ground line or substrate GND. The power bounce and ground bounce are also known as switching noise, and in addition to the common power line VIN and the ground line or substrate GND, they may also introduce mutual interference between the channels through some other common elements, for example bandgap reference generator and comparator.

FIG. 2 is a partially enlarged view of the channel 106 , and FIG. 3 is a waveform diagram of the current I 1 and voltage V 1 on the package inductance Lp 1 of FIG. 2 , in which waveform 200 represents the current I 1 and the other 202 represents the voltage V 1 . Referring to FIGS. 2 and 3 , when the signal U 1 switches the transistor MP 1 , the current I 1 on the package inductance Lp 1 varies, as shown by the waveform 200 , thereby resulting in ripples of the voltage V 1 on the package inductance Lp 1 , as shown by the waveform 202 , and further resulting in the switching noise Snoise on the power line VIN. The greater the variation of the current I 1 is, the greater the switching noise Snoise is. Besides, since all the channels 106 , 108 , . . . , 110 share the common power line VIN, the switching noise Snoise generated on the channel 106 will interfere the other channels 108 , . . . , 110 .

FIG. 4 further illustrates the influence brought by the switching noise Snoise of FIG. 2 , in which waveform 300 represents a threshold Verror 1 , waveform 302 represents the current-sensing signal ISENSE 1 , waveform 304 represents the signal U 1 , waveform 306 represents the switching noise Snoise, waveform 308 represents another threshold Verror 2 , waveform 310 represents the current-sensing signal ISENSE 2 , and waveform 312 represents the signal U 2 . The threshold Verror 1 is produced by amplifying the difference between the feedback signal FB 1 and a preset reference voltage with an error amplifier, and the threshold Verror 2 is also a result of amplifying the difference between the feedback signal FB 2 and the preset reference voltage. Taking the channels 106 and 108 for example, under normal operation, when the signal U 1 turns to low, the transistor MH 1 is turned on and will not be turned off unless the current-sensing signal ISENSE 1 rises up to the threshold Verror 1 , as indicated between time t 1 and time t 2 . Likewise, when the signal U 2 turns to low, the transistor MH 2 is turned on and will not be turned off unless the current-sensing signal ISENSE 2 rises up to the threshold Verror 2 . However, at time t 1 , since the transistor MP 1 is turned on, the switching noise Snoise is produced, as shown by the waveform 306 . When the switching noise Snoise superimposes on the current-sensing signal ISENSE 2 through the common power line VIN, as shown by the waveform 310 , the channel 108 will perform a misoperation and turn off the transistor MH 2 prematurely.

Therefore, it is desired an apparatus and method for preventing a switching converter from misoperation caused by switching noise.

An object of the present invention is to provide an apparatus and method for blanking switching noise in a switching converter.

Another object of the present invention is to provide an apparatus and method for mutual blanking of switching noise in a switching converter.

According to the present invention, a switching converter includes multiple channels. Each channel has an output stage having at least one switch, a current sensor to monitor an output current to generate a first signal, and a controller to generate a second signal according to a first signal to switch the at least one switch to generate the output current. A shutter circuit detects the switching information of the switches of the channels. When one channel performs switching, the shutter circuit generates a blanking signal to block the current sensors of the other channels for a period. The blocked current sensors will not sense the switching noise during the blanking period, and thereby the mutual interference between the channels caused by the switching noise is eliminated.

These and other objects, features and advantages of the present invention will become apparent to those skilled in the art upon consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a conventional multi-channel switching converter;

FIG. 2 is a partially enlarged view of a channel of FIG. 1 ;

FIG. 3 is a waveform diagram of the current and voltage on a package inductance of FIG. 2 ;

FIG. 4 illustrates the influence brought by the switching noise of FIG. 2 ;

FIG. 5 provides one preferred embodiment of the present invention;

FIG. 6 illustrates the operation of the converter of FIG. 5 ;

FIG. 7 shows one preferred embodiment of the shutter circuit of FIG. 5 ; and

FIG. 8 shows one preferred embodiment of the edge detector of FIG. 7 .

As shown in the embodiment of FIG. 5 , in a multi-channel switching converter 400 , an oscillator 402 provides clocks CLK< 1 >, CLK< 2 >, . . . , CLK<N> for channels 406 , 408 , . . . , 410 , respectively. The channel 406 has a driver 414 to generate signals U 1 and L 1 according to a pulse-width modulation signal PWM 1 so as to switch the transistors MH 1 and ML 1 serially connected between a power line VIN and a ground line or substrate GND, thereby generating an output voltage VOUT 1 , voltage divider resistors R 1 and R 2 to divide the output voltage VOUT 1 to generate a feedback signal FB 1 , a current sensor 416 to detect the current flowing through the transistor MH 1 to generate a current-sensing signal ISENSE 1 , and a controller 412 to generate the pulse-width modulation signal PWM 1 according to the current-sensing signal ISENSE 1 and the feedback signal FB 1 . The channel 408 has a driver 420 to generate signals U 2 and L 2 according to a pulse-width modulation signal PWM 2 so as to switch the transistors MH 2 and ML 2 serially connected between the power line VIN and the ground line or substrate GND, thereby generating an output voltage VOUT 2 , voltage divider resistors R 3 and R 4 to divide the output voltage VOUT 2 to generate a feedback signal FB 2 , a current sensor 422 to detect the current flowing through the transistor MH 2 to generate a current-sensing signal ISENSE 2 , and a controller 418 to generate the pulse-width modulation signal PWM 2 according to the current-sensing signal ISENSE 2 and the feedback signal FB 2 . The N-th channel 410 has a driver 426 to generate signals UN and LN according to a pulse-width modulation signal PWMN so as to switch the transistors MHN and MLN serially connected between the power line VIN and the ground line or substrate GND, thereby generating an output voltage VOUTN, voltage divider resistors R 5 and R 6 to divide the output voltage VOUTN to generate a feedback signal FBN, a current sensor 428 to detect the current flowing through the transistor MHN to generate a current-sensing signal ISENSEN, and a controller 424 to generate the pulse-width modulation signal PWMN according to the current-sensing signal ISENSEN and the feedback signal FBN. Particularly, a shutter circuit 404 monitors all the pulse-width modulation signals PWM 1 , PWM 2 , . . . , PWMN of the all channels 406 , 408 , . . . , 410 to extract the switching information of the transistors MH 1 , ML 1 , MH 2 , ML 2 , . . . , MHN, MLN and thereby generates blanking signals BLK 1 , BLK 2 , . . . , BLKN for the channels 406 , 408 and 410 to blank the switching noise caused by the switching of the transistors MH 1 , ML 1 , MH 2 , ML 2 , . . . , MHN, MLN.

FIG. 6 illustrates the operation of the converter 400 of FIG. 5 , in which waveform 500 represents a threshold Verror 1 , waveform 502 represents the current-sensing signal ISENSE 1 , waveform 504 represents the signal U 1 , waveform 506 represents the switching noise Snoise, waveform 508 represents a blanking signal BLK 2 , waveform 510 represents another threshold Verror 2 , waveform 512 represents the current-sensing signal ISENSE 2 , and waveform 514 represents the signal U 2 . The threshold Verror 1 is produced by amplifying the difference between the feedback signal FB 1 and a preset reference voltage with an error amplifier, and the threshold Verror 2 is also a result of amplifying the difference between the feedback signal FB 2 and the preset reference voltage. When the current-sensing signals ISENSE 1 and ISENSE 2 are higher than the thresholds Verror 1 and Verror 2 , respectively, the transistors MH 1 and MH 2 will be turned off. Taking the channels 406 and 408 for example, at time t 1 , in response to the signal U 1 transiting to low, the transistor MH 1 is turned on and will not be turned off unless the current-sensing signal ISENSE 1 rises up to the threshold Verror 1 , as indicated at another time t 2 . Each time the transistor MH 1 is turned on or off, a switching noise Snoise is produced, as shown by the waveform 506 . The shutter circuit 404 monitors the pulse-width modulation signal PWM 1 of the channel 406 , and when the pulse-width modulation signal PWM 1 changes its state to switch the transistor MH 1 , as shown at time t 1 , the shutter circuit 404 swiftly sends out the blanking signal BLK 2 to signal the current sensor 422 of the channel 408 . As a result, during the presence of the switching noise Snoise, the current-sensing signal ISENSE 2 is blocked or the current sensor 422 is blocked so as not to detect the current flowing through the transistor MH 2 , and thereby the switching noise Snoise is prevented from superimposing to the current-sensing signal ISENSE 2 to make the signal U 2 turn on or off the transistor MH 2 at wrong timing.

In this embodiment, each switching noise Snoise is blanked. However, not all the switching noise Snoise will interfere the operation of the channel 408 . For example, when the transistor MH 2 is turned off, since no current flows therethrough, the switching noise Snoise will not affect the channel 408 while the transistor MH 2 is off. Therefore, it is feasible to optionally blank the switching noise Snoise. Alternative to the above embodiment, it may blank the switching noise Snoise by blocking the pulse-width modulation signal PWM 2 . Moreover, the blanking periods of the blanking signals BLK 1 , BLK 2 , . . . , BLKN may vary along with the lengths of the switching noise Snoise.

FIG. 7 shows one preferred embodiment of the shutter circuit 404 of FIG. 5 , in which the pulse-width modulation signals PWM 1 , PWM 2 , . . . , PWMN of the channels 406 , 408 , . . . , 410 are monitored by a respective sub-circuit 600 , and each sub-circuit 600 has an edge detector 604 to detect the rising edge and falling edge of its monitored pulse-width modulation signal so as to generate an edge signal Se, and a one-shot circuit 606 to trigger a signal Sj, j=1, 2, . . . , N. All the signals S 1 , S 2 , . . . , SN are connected to the inputs of an OR gate 602 to determine the blanking signals BLK 1 , BLK 2 , . . . , BLKN. The blanking periods of the signals S 1 , S 2 , . . . , SN may vary along with the lengths of the switching noise Snoise.

FIG. 8 shows one preferred embodiment of the edge detector 604 of FIG. 7 , in which an RC delay circuit 700 delays the pulse-width modulation signal PWM 1 and thereby produces a signal PWM 1 ′, and an exclusive-OR (XOR) gate 702 generates the signal Se according the signals PWM 1 and PWM 1 ′. In this embodiment, when the transistor of any one of the channels is switched to cause a switching noise, the shutter circuit 404 may block all the current-sensing signals or all the current sensors of all the channels. However, in most of cases, a channel is interfered only by the switching noise caused by its adjacent channels, since the channels are switched in sequence. Thus, it may only block for the channels adjacent to the channel that produces the switching noise.

Though in the above description the synchronous current-mode converter are taken as an example to illustrate the principle of the present invention, it is to be understood that the present invention may be also applied to the converters of voltage mode, asynchronous mode, and other modes.

While the invention has been described by way of example and in terms of the preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements as would be apparent to those skilled in the art. Therefore, the scope of the appended claims should be accorded the broadest interpretation to encompass all such modifications and similar arrangements.