HIGH-SPEED LOW-IMPEDANCE BOOSTING LOW-DROPOUT REGULATOR

Abstract

A method for regulating a voltage reference signal includes providing a first output current during a first interval and a boosted output current during a second interval to generate a low-dropout voltage reference signal based on a first power supply voltage, a second power supply voltage, and a reference voltage level. The method includes, during the second interval, compensating for a voltage drop caused by providing the boosted output current. The first output current may be provided in a first mode of operation. The boosted output current and voltage drop compensation may be provided in a boosted mode of operation.

Claims

1.-20. (canceled)

21. A low-dropout regulator comprising: a differential amplifier; an input voltage reference node coupled to a first input of the differential amplifier; a feedback circuit coupled between an output regulated voltage node and a second input of the differential amplifier; an intermediate node between an output of the differential amplifier and the output regulated voltage node; a load stage coupled between the output regulated voltage node and a first power supply node and responsive to a boost control signal; and a compensation stage coupled between a second power supply node and the intermediate node and responsive to a complementary boost control signal.

22. The low-dropout regulator of claim 21 wherein the low-dropout regulator has a first operational mode and a boosting operational mode selectively enabled based on the boost control signal.

23. The low-dropout regulator of claim 22 wherein the boosting operational mode has a high-current operating point that is at least one order of magnitude greater than a first operating point of the first operational mode.

24. The low-dropout regulator of claim 21 further comprising a first device coupled between the first power supply node and the intermediate node and having a first control node coupled to the output of the differential amplifier

25. The low-dropout regulator of claim 24 further comprising a second device coupled between the second power supply node and the output regulated voltage node and having a second control node coupled to the intermediate node.

26. The low-dropout regulator of claim 22 wherein the first device and the second device are configured as common drain amplifiers.

27. A gate driver circuit comprising: an input node configured to receive an input control signal; a low-dropout regulator including a differential amplifier, an input voltage reference node coupled to a first input of the differential amplifier, a feedback circuit coupled between an output regulated voltage node and a second input of the differential amplifier, an intermediate node between an output of the differential amplifier and the output regulated voltage node, a load stage coupled between the output regulated voltage node and a first power supply node and responsive to a boost control signal, and a compensation stage coupled between a second power supply node and the intermediate node and responsive to a complementary boost control signal; a logic circuit configured to generate the boost control signal based on at least the input control signal; and an output node configured to provide an output voltage generated using a regulated output of the low-dropout regulator.

28. The gate driver circuit of claim 27 further comprising: a first driver circuit supplied by the regulated output of the low-dropout regulator and responsive to a first control signal; and a first output device coupled between the first power supply node and the output node and controlled by an output of the first driver circuit.

29. The gate driver circuit of claim 28 further comprising: a second low-dropout regulator responsive to a second boost control signal and configured to provide a second regulated output; a second driver circuit supplied by the second regulated output and responsive to a second control signal; and a second output device coupled between the output node and the second power supply node and controlled by an output of the second driver circuit.

30. The gate driver circuit of claim 29 further comprising a second logic circuit configured to generate the second boost control signal.

31. The gate driver circuit of claim 2 further comprising a non-overlap circuit configured to generate the first control signal and the second control signal based on the input control signal, the first control signal and the second control signal having non-overlapping active levels.

32. A gate driver circuit comprising: an input node configured to receive an input control signal; an output node; a low-dropout regulator configured to provide a first output current during a first interval and a boosted output current during a second interval to generate a low-dropout regulated voltage signal based on a first power supply voltage, a second power supply voltage, and a reference voltage level, and further configured, during the second interval, to compensate for a voltage drop caused by providing the boosted output current; and an output device configured to generate an output voltage based on the input control signal and using the low-dropout regulated voltage signal, and to provide the output voltage on the output node.

33. The gate driver circuit of claim 32 wherein the boosted output current is at least one order of magnitude greater than the first output current.

34. The gate driver circuit of claim 32 wherein the first output current is provided in a first mode of operation and the boosted output current and compensation of the voltage drop are provided in a boosted mode of operation.

35. The gate driver circuit of claim 34 wherein the low-dropout regulator is further configured to provide a current from a first power supply node to a second power supply node in the first mode of operation, the current being substantially less than a second current provided to the second power supply node in the boosted mode of operation.

36. The gate driver circuit of claim 34 wherein the low-dropout regulator is further configured to enable the boosted mode of operation in response to a boost control signal.

37. The gate driver circuit of claim 36 further comprising a logic circuit configured to generate the boost control signal based on the input control signal and a feedback signal.

38. The gate driver circuit of claim 37 wherein the logic circuit is configured to generate the feedback signal based on a comparison of the output voltage to a predetermined voltage level.

39. The gate driver circuit of claim 38 wherein the logic circuit is configured to enable the boost control signal in response to the input control signal having a first signal level and the output voltage not exceeding the predetermined voltage level.

40. The gate driver circuit of claim 39 wherein the logic circuit is further configured to disable the boost control signal in response to the output voltage exceeding the predetermined voltage level or the input control signal having a second signal level.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The present invention may be better understood, and its numerous objects, features, and advantages made apparent to those skilled in the art by referencing the accompanying drawings.

[0008] FIG. 1 illustrates a functional block diagram of an exemplary low-dropout regulator in an exemplary gate driver application.

[0009] FIG. 2 illustrates a circuit diagram of an exemplary low-dropout regulator.

[0010] FIG. 3 illustrates an exemplary circuit diagram of a high-speed low-impedance boosting low-dropout regulator including an n-type output stage consistent with at least one embodiment of the invention.

[0011] FIG. 4 illustrates an exemplary circuit diagram of a high-speed low-impedance boosting low-dropout regulator including a p-type output stage consistent with at least one embodiment of the invention.

[0012] FIG. 5 illustrates an exemplary circuit diagram of the high-speed low-impedance boosting low-dropout regulator including an n-type output stage gate driver of FIG. 3 and a high-speed low-impedance boosting low-dropout regulator including a p-type output stage of FIG. 4 in an exemplary gate driver application consistent with at least one embodiment of the invention.

[0013] FIG. 6 illustrates exemplary timing waveforms for the circuit of FIG. 5 consistent with at least one embodiment of the invention.

[0014] FIG. 7 illustrates an exemplary simplified circuit diagram of a boosted low-dropout regulator including a p-type output stage gate driver and boosted low-dropout regulator including an n-type output stage in the exemplary gate driver application of FIG. 5 and currents associated with a transition of the input control signal consistent with at least one embodiment of the invention.

[0015] The use of the same reference symbols in different drawings indicates similar or identical items.

DETAILED DESCRIPTION

[0016] A high-speed low-impedance boosting low-dropout regulator that maintains a stable output voltage to a load during a transient, high load condition without substantially impacting dynamic performance of the load is disclosed. The high-speed low-impedance boosting low-dropout regulator tolerates high load variation without substantial overshoot or undershoot of the regulated output voltage. Referring to FIG. 3, in at least one embodiment, high-speed low-impedance boosting low-dropout regulator 300 includes two common drain amplifiers (e.g., source follower device SF1_P having a source terminal coupled to node 308 and source follower device SF2_N having a gate terminal coupled to node 308), a load stage 306 including devices of a first type (e.g., n-type transistors), and compensation stage 304 including devices of a second type (e.g., p-type transistors). The output of operational amplifier 302 drives source follower SF1_P with a signal indicating a difference between feedback voltage FB and reference voltage signal V.sub.REF_N. Control signal BOOST enables load stage 306 and a high current operating point of source follower device SF2_N. In at least one embodiment, the high-current operating point is 50 to 100 times higher than a normal operating point, resulting in a reduction of the output impedance by a factor of ten. However, the high current operating point substantially changes gate-to-source voltage V.sub.GS_N across source follower device SF2_N, which is an n-type transistor, resulting in an instantaneous output voltage error. Compensation stage 304 compensates for that change in gate-to-source voltage V.sub.GS_N by also boosting (e.g., according to control signal BOOST_B, which is complementary to control signal BOOST) source follower device SF1_P, to generate current i.sub.BOOST_P that causes a corresponding change to gate-to-source voltage V.sub.GS_P across source follower device SF1_P, which is a p-type transistor (i.e., ΔV.sub.GS_P=ΔV.sub.GS_N), so that regulated output voltage V.sub.REG_N does not change after enabling the boosting mode. In general, due to differences in n-type transistors and p-type transistors, current i.sub.BOOST_P does not equal current i.sub.BOOST_N.

[0017] In a normal mode of operation (i.e., a non-boosting, standby, or lower current mode of operation), both source follower device SF1_P and source follower device SF2_N operate with a corresponding gate-to-source voltage of approximately threshold voltage V.sub.TH. In the boosting mode of operation, the gate-to-source voltage increases, causing the current to increase by 50 to 100 times, and source follower device SF1_P and source follower device SF2_N both transition to an operating point having a significant saturation voltage V.sub.DSAT (i.e., a minimum drain-to-source voltage required to maintain the transistor in the saturation region of operation). Bias voltage VBP1 determines a standby current (i.e., the current in the normal mode of operation). The standby current and the boosting current, and sizes of corresponding devices, have a ratio of 1:N (e.g., N=50 or 100). An auxiliary loop sets bias voltage VBP2, which ensures that in the boosting mode of operation, the saturation voltages of the source followers are equal, i.e., V.sub.DSATP=V.sub.DSATN. If that condition is met, then the feedback voltage does not change in the boosting mode of operation, and the output of operational amplifier 302 is stable, thus, rendering unnecessary the fast feedback loop of the low-dropout regulator described above.

[0018] FIG. 4 illustrates high-speed low-impedance boosting low-dropout regulator 400 having a circuit implementation that is complementary to the circuit implementation of high-speed low-impedance boosting low-dropout regulator 300 of FIG. 3 and generates regulated output voltage VREG_P. High-speed, boosting low-dropout regulator 400 includes two common drain amplifiers (e.g., source follower device SF1_N having a source terminal coupled to node 408 and source follower device SF2_P having a gate terminal coupled to node 408), load stage 406 including devices of the second type (e.g., p-type transistors), and compensation stage 404 including devices of the first type (e.g., n-type transistors). The output of operational amplifier 402 drives source follower SF1_N with a signal indicating a difference between feedback voltage FB and reference voltage signal V.sub.REF_P. Control signal BOOST_B enables load stage 406 and a high current operating point of source follower device SF2_P. The high current operating point substantially changes gate-to-source voltage V.sub.GS_P across source follower device SF2_P, which is a p-type transistor, resulting in an instantaneous output voltage error. Compensation stage 404 compensates for that change in gate-to-source voltage V.sub.GS_P by also boosting (e.g., using control signal BOOST) source follower device SF1_N, to generate current i.sub.BOOST_N that causes a corresponding change to gate-to-source voltage V.sub.GS_N across source follower device SF1_N, which is an n-type transistor (i.e., ΔV.sub.GS_P=ΔV.sub.GS_N), so that regulated output voltage V.sub.REG_P does not change after enabling the boosting mode.

[0019] FIGS. 5 and 6 illustrate an exemplary embodiment of a gate driver circuit including output transistor M.sub.1, driven using high-speed low-impedance boosting low-dropout regulator 300, and output transistor M.sub.2, driven using high-speed low-impedance boosting low-dropout regulator 400, and associated control circuitry. Output transistor M.sub.1 and output transistor M.sub.1 are coupled to drive load C.sub.LOAD and are driven according to input control signal IN. In at least one embodiment, circuit 500 generates control signal BOOST.sub.P and control signal BOOST.sub.N that enable the boosting modes of high-speed low-impedance boosting low-dropout regulator 400 and high-speed low-impedance boosting low-dropout regulator 300, respectively, only when needed. Circuit 500 starts the boosting in response to a transition of input control signal IN (i.e., a rising edge or a falling edge of input control signal IN) by generating control signal IN.sub.P and control signal IN.sub.N, which are non-overlapping versions of the input signal that control output transistor M.sub.2 and output transistor M.sub.1, respectively.

[0020] In an exemplary embodiment, boosting begins at the transition of input control signal IN and the turn-on or turn-off of an output transistor (e.g., output transistor M.sub.2 or output transistor M.sub.1). Non-overlap circuit 510 generates a delay, which provides sufficient time for the boost control switches to turn on the boosting current in the regulator output stages. Circuit 500 disables the boosting mode of operation before the end of the transition of output signal OUT. Comparator 506 and comparator 508 detect the desaturation point of output transistor M.sub.2 and output transistor M.sub.1, respectively, by comparing the drain voltages to reference voltage V.sub.REFP and reference voltage V.sub.REFN, respectively, and generating corresponding signals indicative of those comparisons that are combined with control signal IN.sub.P and control signal IN.sub.N, respectively, to generate control signal BOOST.sub.P and control signal BOOST.sub.N, respectively. In at least one embodiment, control signal BOOST.sub.P is generated by a logical AND of the output of comparator 506 and input control signal IN and control signal BOOST.sub.N is generated by a logical NOR of the output of comparator 508 and input control signal IN. However, in other embodiments, other logical circuits are used instead of AND gate 512 and NOR gate 514 to generate control signal BOOST.sub.P and control signal BOOST.sub.N consistent with the description above. In at least one embodiment, circuit 500 has fast current settling performance (e.g., 10-20 ns) without large on-chip capacitors (e.g., nano-Farads) or large off-chip capacitors.

[0021] Referring to FIG. 7, in at least one embodiment, in response to a rising edge of input control signal IN, the boosting current increases the current consumption from 1 mA to 10 mA during a transient of input signal IN of circuit 500 in the boosting mode of operation. Current i.sub.BOOST_P (e.g., 10 mA) flows through both power supply nodes and can be sensed on the ground pin. Current i.sub.BOOST_P ceases when the voltage on node OUT approaches the supply voltage. The output current (e.g., i.sub.OUT=2-6 Amperes(A)) flows through only one of the power supply nodes (e.g., from node V.sub.DD, through output transistor M.sub.2, and through node OUT). Charging of a parasitic capacitance CGD_N of output transistor M.sub.1 generates current i.sub.C_N that flows from node OUT and through node GND. However, using a high load capacitance (e.g., C.sub.LOAD=100 nF) results in a low change in voltage over time at node OUT and current i.sub.C_N stays below 1 mA (e.g., i.sub.C_N=0.5 mA), which is much less than current i.sub.BOOST_P.

[0022] Thus, a high-speed low-impedance boosting low-dropout regulator that provides a regulated output voltage to a load during a transient, high load condition over a short period of time without substantially impacting the dynamic performance of the load or substantial increase in average current is disclosed. The high-speed low-impedance boosting low-dropout regulator supports a low output impedance without significant overshoot or undershoot, does not need a large bypass capacitance, and may be operated without a bypass capacitance.

[0023] The description of the invention set forth herein is illustrative and is not intended to limit the scope of the invention as set forth in the following claims. For example, while the invention has been described in an embodiment in which a high-speed low-impedance boosting low-dropout regulator is implemented in a gate driver application, one of skill in the art will appreciate that the teachings herein can be utilized with other applications. The terms “first,” “second,” “third,” and so forth, as used in the claims, unless otherwise clear by context, is to distinguish between different items in the claims and does not otherwise indicate or imply any order in time, location or quality. Variations and modifications of the embodiments disclosed herein may be made based on the description set forth herein, without departing from the scope of the invention as set forth in the following claims.