Power management system for integrated circuit

A power management system for an integrated circuit (IC) includes low and full-power bandgap generators, first and second multiplexers, first circuitry, and a full-power regulator. When the IC is powered on, the first multiplexer selects the full-power bandgap generator as a reference voltage source for the first circuitry. After the low-power bandgap generator has been trimmed, the first multiplexer selects the low-power bandgap generator as the reference voltage source for the first circuitry. When the IC transitions from low power mode to high power mode, the second multiplexer selects the low-power bandgap generator as the reference voltage source for the full-power regulator. When the full-power bandgap generator is powered on, the second multiplexer selects the full-power bandgap generator as the reference voltage source for the full-power regulator.

BACKGROUND OF THE INVENTION

The present invention relates generally to integrated circuits, and, more particularly, to a power management system for an integrated circuit.

Integrated circuits (ICs) including system-on-chips (SoCs) integrate various digital and sometimes also analog components on a single chip. Many ICs further include different power domains such as high and low power domains. The high power domain includes components that operate when the IC is in a high power mode and powered down when the IC is in a low power mode. The low power domain includes components that operate when the IC is in the high and low power modes. ICs with multiple power domains require multiple supply voltages that are provided by multiple voltage regulators. The high power domain is served by a high power voltage regulator (hereinafter referred to as a “full-power regulator”) and the low power domain is served by a low power voltage regulator (hereinafter referred to as a “low-power regulator”). The low-power regulator is operational when the IC is in the low power mode and hence, the low-power regulator is designed to consume less power than the full-power regulator.

Such ICs also include a power management controller (PMC) that monitors the operating voltage of the IC. The PMC includes voltage monitoring circuits such as low-voltage detection (LVD) and high-voltage detection (HVD) circuits. The LVD circuits monitor the operating voltage of the IC and compare it with an LVD threshold voltage. The LVD threshold voltage represents the lowest voltage level at which the IC can operate without failing or deviating from the functional specification of the IC. Therefore, when the operating voltage drops below the LVD threshold voltage, the LVD circuit generates a safe-state signal to configure the IC in a reset or safe-state mode. Similarly, the HVD circuit configures the IC in the reset or safe-state mode when the operating voltage exceeds an HVD threshold voltage, in order to prevent the over-voltage condition from damaging the IC.

The above-mentioned voltage regulators and voltage monitoring circuits operate using reference voltage signals received from bandgap voltage reference generators. A bandgap voltage reference generator (hereinafter referred to as “bandgap generator”) is a reference voltage circuit that outputs a reference voltage signal at a fixed voltage level irrespective of environmental changes such as ambient temperature changes, power supply variations and load variation. Generally, the low-power regulator and voltage monitoring circuits receive a first reference voltage signal from a low-power bandgap generator and the full-power regulator receives a second reference voltage signal from a full-power bandgap generator. The low-power regulator and voltage monitoring circuits are operational when the IC is in the low power mode. Therefore, the low-power bandgap generator also is operational when the IC is in the low power mode and hence, the low-power bandgap generator is designed to consume less power than the full-power bandgap generator.

FIG. 1shows an IC100operable in high and low power modes and that has a conventional power management system101. The power management system101includes a low-power bandgap generator102and first circuitry104. When the IC100is in either the high or low power mode, the low-power bandgap generator102generates and provides a low-power bandgap reference voltage signal (VLPBG—REF) to the first circuitry104. The first circuitry104includes a low-power regulator (not shown) and voltage monitoring circuits (not shown) such as LVD and HVD modules. For example, the first circuitry104may include an LVD module106. The LVD module106receives the low-power bandgap reference voltage signal (VLPBG—REF) that is at a voltage level of a LVD threshold voltage and a supply voltage (VSUPPLY) indicative of an operating voltage of the IC100, and outputs an LVD signal (high active) when the supply voltage (VSUPPLY) is greater than the low-power bandgap reference voltage signal (VLPBG—REF). To ensure proper operation of the LVD module106, the LVD threshold voltage is designed to lie within a designated voltage range. When the IC100is powered on after a power-on-reset (POR), the low-power bandgap generator102is in an untrimmed condition for a first predetermined time period after the POR and hence, the accuracy of the low-power bandgap reference voltage signal (VLPBG—REFF) is low. The low-power bandgap generator102is trimmed and the low-power bandgap reference voltage signal (VLPBG—REF) is stabilized after the first predetermined time period after the POR.

During the first predetermined time period, the low-power bandgap reference voltage signal (VLPBG—REF) is unstable and has low accuracy and hence, may not be within the designated voltage range. Thus, the LVD module106may not assert when the supply voltage (VSUPPLY) is less than the LVD threshold voltage, which could cause a failure or deviation from the functional specification of the IC100. Further, low-power consumption requirements of the IC100constrain the efforts to design a high accuracy low-power bandgap generator. Designing an improved low-power bandgap generator102is difficult and requires additional components that result in an increase in the area overhead, power consumption and cost of production.

FIG. 2shows an IC200operable in high and low power modes and that includes a conventional power management system201. The power management system201includes a full-power bandgap generator202, a soft-start circuit204connected to the full-power bandgap generator202, a first multiplexer206connected to the soft-start circuit204and the full-power bandgap generator202, and a full-power regulator208connected to the first multiplexer206. When the IC200transitions from low power mode to high power mode, the full-power regulator208is powered on and operates in a voltage build-up phase. The full-power bandgap generator202is powered on and generates a full-power bandgap reference voltage signal (VFPBG—REF). The soft-start circuit204receives the full-power bandgap reference voltage signal (VFPBG—REF), and outputs an intermediate reference voltage signal (VINT—REF) having a controlled ramp-up rate. The first multiplexer206receives and outputs the intermediate reference voltage signal (VINT—REF) to the full-power regulator208when the full-power regulator208is in the voltage build-up phase.

When the voltage level of the intermediate reference voltage signal (VINT—REF) exceeds a first threshold voltage level, the soft-start circuit204generates a soft-start complete signal (VSOFT—START—COMPLETE) to indicate the completion of the voltage build-up phase. The first multiplexer206receives the soft-start complete signal (VSOFT—START—COMPLETE) at a select terminal thereof and outputs the full-power bandgap reference voltage signal (VFPBG—REF) to the full-power regulator208. The full-power regulator208receives the full-power bandgap reference voltage signal (VFPBG—REF) and starts operating in a full-regulation phase. The full-power regulator208reaches a stable operation state in the full-regulation phase. Thus, when the IC200transitions from low power mode to high power mode, the full-power regulator208starts operating in the voltage build-up phase only when the full-power bandgap generator202is powered on. The time required for the IC200to transition from the low power mode to the high power mode is defined as a low power wake-up time. Since the full-power regulator208waits for the full-power bandgap generator202to be powered on, the low power wake-up time of the IC200increases. Thus, the performance of the IC200is affected.

It would be advantageous to have a power management system for an integrated circuit that provides accurate reference voltage to voltage regulators and voltage monitoring circuits to the integrated circuit, prevents damage and improves the performance of the integrated circuit, and overcomes the above-mentioned limitations of conventional power management systems.

DETAILED DESCRIPTION OF THE INVENTION

In an embodiment of the present invention, a power management system for an integrated circuit (IC), where the IC is operable in a low power mode and a high power mode, is provided. The system includes low-power and full-power bandgap generators, a reset mode controller, a first multiplexer and first circuitry. The low-power bandgap generator is powered on when the IC enters high power mode after a power-on-reset (POR) and provides a first reference voltage signal when the IC is in the high and low power modes. The full-power bandgap generator is powered on when the IC enters the high power mode, provides a second reference voltage signal when the IC is in the high power mode, and is powered off when the IC is in the low power mode. The reset mode controller is connected to the low-power and full-power bandgap generators. The reset mode controller stabilizes the first and second reference voltage signals when the IC enters the high power mode after the POR, and generates a stabilization complete signal when the first reference voltage signal is stabilized. The reset mode controller stabilizes the first reference voltage signal in a first predetermined time period after the POR. The first multiplexer has a first input terminal connected to the low-power bandgap generator for receiving the first reference voltage signal, a second input terminal connected to the full-power bandgap generator for receiving the second reference voltage signal, a select input terminal connected to the reset mode controller for receiving the stabilization complete signal, and an output terminal for outputting one of the first and second reference voltage signals. First circuitry is connected to the output terminal of the first multiplexer. The first circuitry receives the second reference voltage signal during the first predetermined time period and the first reference voltage signal when the stabilization complete signal is generated (i.e., when the stabilization signal is active).

In another embodiment of the present invention, a power management system for an integrated circuit (IC) that is operable in low power and high power modes is provided. The system includes low-power and full-power bandgap generators, a first multiplexer, a soft-start circuit, and a full-power regulator. The low-power bandgap generator provides a first reference voltage signal (when the IC is in either of the low and high power modes). The full-power bandgap generator provides a second reference voltage signal when the IC is in the high power mode, and is powered off when the IC is in the low power mode. The soft-start circuit is connected to the low-power bandgap generator. The soft-start circuit receives the first reference voltage signal and generates an intermediate reference voltage signal when the IC transitions from the low power mode to the high power mode, and generates a soft-start complete signal when the intermediate reference voltage signal reaches a threshold voltage level. The intermediate reference voltage signal reaches the threshold voltage level within a first predetermined time period after the IC exits the low power mode and transitions to the high power mode. The first multiplexer has a first input terminal connected to the soft-start circuit for receiving the intermediate reference voltage signal, a second input terminal connected to the full-power bandgap generator for receiving the second reference voltage signal, a select input terminal connected to the soft-start circuit for receiving the soft-start complete signal, and an output terminal for outputting one of the intermediate and second reference voltage signals. The full-power regulator is connected to the output terminal of the first multiplexer and receives the intermediate reference voltage signal during the first predetermined time period and the second reference voltage signal when the soft-start complete signal is generated.

In yet another embodiment of the present invention, a power management system for an integrated circuit (IC) is provided, where the IC is operable in low and high power modes. The IC includes low-power and full-power bandgap generators, a reset mode controller, first and second multiplexers, first circuitry, a soft-start circuit, and a full-power regulator. The low-power bandgap generator is powered on when the IC enters the high power mode after a power-on-reset (POR) and provides a first reference voltage signal. The full-power bandgap generator is powered on when the IC enters the high power mode, provides a second reference voltage signal when the IC is in the high power mode, and is powered off when the IC is in the low power mode. The reset mode controller is connected to the low-power and full-power bandgap generators. The reset mode controller stabilizes the first and second reference voltage signals when the IC enters the high power mode after the POR, and generates a stabilization complete signal when the first reference voltage signal is stabilized. The reset mode controller stabilizes the first reference voltage signal within a first predetermined time period after the POR. The first multiplexer has a first input terminal connected to the low-power bandgap generator for receiving the first reference voltage signal, a second input terminal connected to the full-power bandgap generator for receiving the second reference voltage signal, a select input terminal connected to the reset mode controller for receiving the stabilization complete signal, and an output terminal for outputting one of the first and second reference voltage signals. The first circuitry is connected to the output terminal of the first multiplexer. The first circuitry receives the second reference voltage signal during the first predetermined time period and the first reference voltage signal when the stabilization complete signal is generated. The soft-start circuit is connected to the low-power bandgap generator. The soft-start circuit receives the first reference voltage signal and generates an intermediate reference voltage signal when the IC transitions from the low power mode to the high power mode, and generates a soft-start complete signal when the intermediate reference voltage signal reaches a threshold voltage level. The intermediate reference voltage signal reaches the threshold voltage level within a second predetermined time period after the IC exits the low power mode and transitions to the high power mode. The second multiplexer has a first input terminal connected to the soft-start circuit for receiving the intermediate reference voltage signal, a second input terminal connected to the full-power bandgap generator for receiving the second reference voltage signal, a select input terminal connected to the soft-start circuit for receiving the soft-start complete signal, and an output terminal for outputting one of the intermediate and second reference voltage signals. The full-power regulator is connected to the output terminal of the second multiplexer. The full-power regulator receives the intermediate reference voltage signal during the second predetermined time period and the second reference voltage signal when the soft-start complete signal is generated.

Various embodiments of the present invention provide a power management system for an IC that is operable in low power and high power modes. The system includes low-power and full-power bandgap generators, a reset mode controller, first and second multiplexers, first circuitry, a soft-start circuit, and a full-power regulator. The first circuitry includes components such as low-voltage detection (LVD) modules that are operational when the IC is in the low power mode. The low-power bandgap generator is powered on when the IC enters the high power mode after a power-on-reset (POR) and provides a first reference voltage signal. The full-power bandgap generator is powered on when the IC enters the high power mode, provides a second reference voltage signal when the IC is in the high power mode, and is powered off when the IC is in the low power mode.

The reset mode controller stabilizes the first and second reference voltage signals when the IC enters the high power mode after the POR, and generates a stabilization complete signal when the first reference voltage signal is stabilized. The reset mode controller stabilizes the first reference voltage signal within a first predetermined time period after the POR. During the first predetermined time period, the second reference voltage signal is more stable as compared to the first reference voltage signal, and hence the second reference voltage signal has a higher accuracy. The first multiplexer outputs the second reference voltage signal to the first circuitry during the first predetermined time period after the POR and outputs the first reference voltage signal to the first circuitry when the stabilization complete signal is generated.

The soft-start circuit receives the first reference voltage signal and generates an intermediate reference voltage signal when the IC transitions from the low power mode to the high power mode, and generates a soft-start complete signal when the intermediate reference voltage signal reaches a threshold voltage level. The intermediate reference voltage signal reaches the threshold voltage level within a second predetermined time period after the IC exits the low power mode and transitions to the high power mode. The second multiplexer outputs the intermediate reference voltage signal to the full-power regulator during the second predetermined time period and the second reference voltage signal to the full-power regulator when the soft-start complete signal is generated.

Thus, the first circuitry receives the second reference voltage signal when the first reference voltage signal is being stabilized, thereby receiving a stable reference voltage signal, and ensuring proper operation of the first circuitry. Further, when the IC transitions from the low power mode to the high power mode, the full-power regulator receives the intermediate reference voltage signal and starts operating. Since the full-power regulator is not required to wait for the full-power bandgap generator to be powered on, the low power wake-up time of the IC is fast, thereby improving the performance of the IC.

Referring now toFIG. 3, a schematic block diagram of an integrated circuit (IC)300in accordance with an embodiment of the present invention is shown. The IC300is operable in low power and high power modes and includes a power management system301. The power management system301includes low-power and full-power bandgap generators302and304, a reset mode controller306, a first multiplexer or mux308, and first circuitry310.

The low-power bandgap generator302is used as a source of reference voltage for various components of the IC300, such as the first circuitry310, that are operational when the IC300is in the high and low power modes. When the IC300is powered on after a power-on-reset (POR), a power management controller (PMC, not shown) powers on the low-power bandgap generator302. When the IC300is transitioning to the high power mode after the POR, the low-power bandgap generator302operates in an untrimmed condition, and hence generates an unstable first reference voltage signal (VLPBG—REF) having low accuracy. When the IC300is in the high and low power modes, the low-power bandgap generator302operates in a trimmed condition and hence, generates a stable first reference voltage signal (VLPBG—REF) having a higher accuracy as compared to the unstable first reference voltage signal (VLPBG—REF). Generally, to meet the low power consumption requirements of the low power mode, the low-power bandgap generator302is designed to consume less power than the full-power bandgap generator304. Therefore, the low-power bandgap generator302is less accurate than the full-power bandgap generator304. The low-power bandgap generator302includes a first set of switches that is switched on or off based on a first set of trimming codes. The operation state of the first set of switches determines a voltage level of the first reference voltage signal (VLPBG—REF), thereby allowing adjustments to be made to the voltage level of the first reference voltage signal (VLPBG—REF).

The full-power bandgap generator304is used as a source of reference voltage for various components of the IC300, such as the full-power regulators (not shown) that are operational when the IC300is in the high power mode. When the IC300is powered on after a power-on-reset (POR), the PMC powers on the full-power bandgap generator304. When the IC300transitions to the high power mode after the POR, the full-power bandgap generator304operates in the untrimmed condition and hence, generates an unstable second reference voltage signal (VFPBG—REF). When the IC300is in the high power mode, the full-power bandgap generator304operates in the trimmed condition and hence, generates a stable second reference voltage signal (VFPBG—REF) having higher accuracy than the unstable second reference voltage signal (VFPBG—REF). To meet the low power consumption requirements of the low power mode, the full-power bandgap generator304is switched off when the IC300is in the low power mode.

When the IC300transitions from the low power mode to the high power mode, the PMC powers on the full-power bandgap generator304. Since the full-power bandgap generator304is not constrained by any low power consumption requirements, the full-power bandgap generator304is designed to be more accurate than the low-power bandgap generator302. Due to the differences in the design and constitution between the low-power and full-power bandgap generators302and304, the unstable second reference voltage signal (VFPBG—REF) is more accurate than the unstable first reference voltage signal (VLPBG—REF). The full-power bandgap generator304includes a second set of switches that is switched on or off based on a second set of trimming codes. The operational state of the second set of switches determines a voltage level of the second reference voltage signal (VFPBG—REF), thereby allowing adjustments to be made to the voltage level of the second reference voltage signal (VFPBG—REF).

The reset mode controller306is connected to the low-power and full-power bandgap generators302and304. When the IC300transitions to the high power mode after the POR, the PMC powers on the reset mode controller306after the low-power and full-power bandgap generators302and304are powered on. The reset mode controller306retrieves the first and second sets of trimming codes from an internal memory (not shown) such as a ROM. The reset mode controller306controls the operational states of the first and second sets of switches by providing the first and second sets of trimming codes to the low-power and full-power bandgap generators302and304, respectively. Thus, the reset mode controller306adjusts the voltage levels of the first and second reference voltage signals (VLPBG—REFand VFPBG—REF) using the first and second sets of trimming codes, thereby stabilizing the first and second reference voltage signals (VLPBG—REFand VFPBG—REF).

The reset mode controller306stabilizes the unstable first and second reference voltage signals (VLPBG—REFand VFPBG—REF) within a first predetermined time period after the POR and generates a stabilization complete signal (VSTB—CMP) when the first reference voltage signal (VLPBG—REF) is stabilized. The aforementioned procedure of adjusting the voltage levels of the first and second reference voltage signals (VLPBG—REFand VFPBG—REF) is termed as trimming and is understood by those of skill in the art. Hence, further explanation thereof is not required for a complete understanding of the present invention.

The first mux308has a first input terminal connected to the low-power bandgap generator302for receiving the first reference voltage signal (VLPBG—REF), a second input terminal connected to the full-power bandgap generator304for receiving the second reference voltage signal (VFPBG—REF) a select input terminal connected to the reset mode controller306for receiving the stabilization complete signal (VSTB—CMP), and an output terminal for outputting one of the first and second reference voltage signals (VLPBG—REFand VFPBG—REF). When the IC300transitions to the high power mode after the POR, the first mux308outputs the second reference voltage signal (VFPBG—REF) for the first predetermined time period. After the first predetermined time period, the first mux308receives the stabilization complete signal (VSTB—CMP) at its select input terminal and outputs the first reference voltage signal (VLPBG—REF).

The first circuitry310is connected to the output terminal of the first mux308for receiving the selected one of the first and second reference voltage signals (VLPBG—REFand VFPBG—REF). The first circuitry310includes various analog and digital components that are operational when the IC300is in the low and high power modes. The first circuitry310may include a low-power regulator (not shown) and voltage monitoring circuits (not shown) such as LVD and HVD modules. For example, the first circuitry310includes an LVD module312. The LVD module312has an inverting terminal connected to the output terminal of the first mux308for receiving the selected one of the first and second reference voltage signals (VLPBG—REFand VFPBG—REF), a non-inverting terminal connected to a supply voltage indicative of an operating voltage of the IC300, and an output terminal for generating an LVD signal when the supply voltage exceeds one of the first and second reference voltage signals (VLPBG—REFand VFPBG—REF).

In operation, when the IC300is powered on after the POR, the PMC powers on the low-power and full-power bandgap generators302and304. The PMC further powers on the reset mode controller306. The low-power and full-power bandgap generators302and304generate the first and second reference voltage signals (VLPBG—REFand VFPBG—REF), respectively, which may be unstable for the first predetermined time period. During the first predetermined time period, the first mux308outputs the second reference voltage signal (VFPBG—REF) to the first circuitry310. The first circuitry310receives the second reference voltage signal (VFPBG—REF), which is more accurate than the first reference voltage signal (VLPBG—REF) at this time. Thus, the system301prevents malfunctioning of the first circuitry310. Further, the need for designing an improved low-power bandgap generator302with higher accuracy is averted, thereby reducing cost of production, power consumption and area overhead of the IC300.

During the first predetermined time period, the reset mode controller306retrieves the first set of trimming codes from the internal memory and trims the low-power bandgap generator302, thereby stabilizing the first reference voltage signal (VLPBG—REF). The reset mode controller306then generates the stabilization complete signal (VSTB—CMP). The first mux308receives the stabilization complete signal (VSTB—CMP) and outputs the stable first reference voltage signal (VLPBG—REF) to the first circuitry310. Thus, after the first predetermined time period, the low-power bandgap generator302provides the stable first reference voltage signal (VLPBG—REF) as a reference voltage to the first circuitry310, thereby ensuring continuous operation of the first circuitry310when the IC300transitions from the high power mode to the low power mode.

Referring now toFIG. 4, a schematic block diagram of an integrated circuit (IC)400in accordance with another embodiment of the present invention is shown. The IC400is operable in low power and high power modes, and includes high and low power domains (not shown). The IC400includes a power management system401. The power management system401includes the low-power and full-power bandgap generators302and304, a soft-start circuit402, a second mux404, and a full-power regulator406. Generally, the full-power bandgap generator304, the soft-start circuit402and the full-power regulator406are included in the high power domain.

The soft-start circuit402is connected to the low-power bandgap generator302for receiving the first reference voltage signal (VLPBG—REF) when the IC400transitions from the low power mode to the high power mode. The soft-start circuit402receives the first reference voltage signal (VLPBG—REF) and outputs an intermediate reference voltage signal (VINT—REF) having a controlled ramp-up rate based on the first reference voltage signal (VLPBG—REFF). The soft-start circuit402provides the intermediate reference voltage signal (VINT—REF) to the full-power regulator406, thereby controlling the ramp-up rate of the full-power regulator406. The intermediate reference voltage signal (VINT—REF) reaches a threshold voltage level within a second predetermined time period after the IC400exits the low power mode and transitions to the high power mode. The soft-start circuit402generates a soft-start complete signal (VSOFT—START—COMPLETE) when the intermediate reference voltage signal (VINT—REF) reaches the threshold voltage level. The soft-start circuit402ceases to control the ramp-up rate of the full-power regulator406when the intermediate reference voltage signal (VINT—REF) exceeds the threshold voltage level. For example, the soft-start circuit402may include a slew rate controller (not shown) to limit an in-rush current to the full-power regulator406that receives the intermediate reference voltage signal (VINT—REF) during the second predetermined time period, thereby controlling the ramp-up rate of the full-power regulator406. The in-rush current is generated due to abrupt powering up of the high power domain when the full-power regulator406is powered on without a controlled ramp-up rate.

The second mux404has a first input terminal connected to the soft-start circuit402for receiving the intermediate reference voltage signal (VINT—REF), a second input terminal connected to the full-power bandgap generator304for receiving the second reference voltage signal (VFPBG—REF) a select input terminal connected to the soft-start circuit402for receiving the soft-start complete signal (VSOFT—START—COMPLETE), and an output terminal for outputting one of the intermediate and second reference voltage signals (VINT—REFand VFPBG—REF) to the full-power regulator406. When the IC400transitions from the low power mode to the high power mode, the second mux404outputs the intermediate reference voltage signal (VINT—REF) to during the second predetermined time period. After the second predetermined time period, the second mux404receives the soft-start complete signal (VSOFT—START—COMPLETE) at its select input terminal and outputs the second reference voltage signal (VFPBG—REF).

The full-power regulator406is connected to the output terminal of the second mux404for receiving the selected one of the first and second reference voltage signals (VLPBG—REFand VFPBG—REF). The full-power regulator406is operational when the IC400is in the high power mode and is switched off when the IC400is in the low power mode. When the IC transitions from the low power mode to the high power mode, the full-power regulator406is powered on and the soft-start circuit402provides the intermediate reference voltage signal (VINT—REF) to the full-power regulator406, thereby controlling the ramp-up rate of the full-power regulator406. The full-power regulator406receives one of the intermediate and second reference voltage signals (VINT—REFand VFPBG—REF) as a reference voltage signal and regulates an output voltage signal at a first voltage level based on the reference voltage signal.

In operation, when the IC400transitions from the low power mode to the high power mode, the PMC powers on the soft-start circuit402and the full-power bandgap generator304. Since the IC400transitions from the low power mode, the low-power bandgap generator302is operational and generates the stable first reference voltage signal (VLPBG—REF) while the IC400transitions from the low power mode to the high power mode. The soft-start circuit402receives the stable first reference voltage signal (VLPBG—REF) and outputs the intermediate reference voltage signal (VINT—REF). The second mux404receives and outputs the intermediate reference voltage signal (VINT—REF) to the full-power regulator406during the second predetermined time period. Thus, when the IC400transitions from the low power mode to the high power mode, the full-power regulator406starts operating as the low-power bandgap generator302is operational. Therefore, the time required for the IC400to transition from the low power mode to the high power mode decreases because the full-power regulator406does not have to wait for the full-power bandgap generator304to be powered on and operational. Thus, the low-power wakeup time of the IC400is reduced (the IC400wakes up faster) and so the performance of the IC400is improved.

During the second predetermined time period, the full-power bandgap generator304powers on, starts operating, and generates the second reference voltage signal (VFPBG—REF). After the second predetermined time period, the intermediate reference voltage signal (VINT—REF) exceeds the threshold voltage level so the soft-start circuit402generates the soft-start complete signal (VSOFT—START—COMPLETE). The second mux404receives the soft-start complete signal (VSOFT—START—COMPLETE) and outputs the second reference voltage signal (VFPBG—REF) to the full-power regulator406. Thus, the reference voltage to the full-power regulator406is switched between the first and second reference voltage signals (VLPBG—REFand VFPBG—REF) to reduce the transition time of the IC400from the low power mode to the high power mode.

Referring now toFIG. 5, a schematic block diagram of an integrated circuit (IC)500in accordance with yet another embodiment of the present invention is shown. The IC500is operable in low power and high power modes and includes a power management system501. The power management system501is implemented using a combination of the power management systems301and401and includes the low-power and full-power bandgap generators302and304, the reset mode controller306, the first mux308, the first circuitry310, the soft-start circuit402, the second mux404, and the full-power regulator406. The IC500is functionally similar to ICs300and400as described inFIGS. 3 and 4, thus the explanation of these components is not repeated.