Abstract:
A voltage regulator includes a voltage source for providing an input voltage. The regulator includes circuitry responsive to the input voltage for generating a regulated output voltage. The circuitry enables selection of one of internal linear voltage regulation or external linear voltage regulation for generating the regulated output voltage.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority from pending U.S. Provisional Application Ser. No. 60/553,489 (Atty. Dkt. No. INTS-26,689) entitled “CONFIGURABLE INTERNAL/EXTERNAL LINEAR VOLTAGE REGULATOR”. 
     
    
     TECHNICAL FIELD OF THE INVENTION  
       [0002]     The present invention relates to voltage regulators, and more particularly, to a voltage regulator that has a user programmable internal pass/external pass feature.  
       BACKGROUND OF THE INVENTION  
       [0003]     Every electronic circuit is designed to operate off of some supply voltage, which is usually assumed to be constant. A voltage regulator provides this constant DC output voltage and contains circuitry that continuously holds the output voltage at a regulated value regardless of changes in a load current or input voltage. A linear voltage regulator operates by using a voltage controlled current source to output a fixed voltage. A control circuit must monitor the output voltage, and adjust the current source to hold the output voltage at the desired value.  
         [0004]     One of the problems that a wide range input voltage, such as 3 v to 20 v, places on a linear voltage regulator is thermal stress when operating at high input supply voltage while providing a low output voltage. This is further compounded when the linear regulator is only one aspect of the total chip functionality, and the total thermal budget cannot be used up by the Linear Regulator. Most of the thermal stress is on the current source and the exact magnitude of the problem is very application specific. The easiest way to control the problem is to control the current source by allowing it to be either internal or external. Existing linear voltage regulators are unable to be configured with either internal or external current sources.  
       SUMMARY OF THE INVENTION  
       [0005]     The present invention disclosed and claimed herein, in one aspect thereof, includes a voltage regulator that is capable of operating with either an internal voltage regulator or an external voltage regulator. The regulator includes a voltage source for providing an input voltage. Circuitry responsive to the input voltage generates a regulated voltage output. The circuitry enables selection of one of an internal linear voltage regulator for internal linear voltage regulation or an external linear voltage regulator for external linear voltage regulation for generating the regulated voltage output.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]     For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following description taken in conjunction with the accompanying Drawings in which:  
         [0007]      FIG. 1  is a block diagram of a linear voltage generator;  
         [0008]      FIG. 2  is a block diagram illustrating a configurable internal/external linear voltage regulator;  
         [0009]      FIGS. 3   a  and  3   b  illustrate the manner in which the LIN_DRV pin is connected with respect to operation as an external linear voltage regulator;  
         [0010]      FIG. 4  is a schematic diagram of one embodiment of a simple transconductance amplifier for use within the configurable linear voltage regulator of  FIG. 2 ;  
         [0011]      FIG. 5  is a schematic diagram of the linear voltage regulator configured as an internal linear voltage regulator; and  
         [0012]      FIG. 6  is a schematic diagram of the voltage regulator configured as an external linear voltage regulator.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0013]     Every electronic circuit is designed to operate off of some voltage supply, which is usually assumed to be constant. A voltage regulator provides a constant DC output voltage and contains circuitry that continuously holds the output voltage at the designed value regardless of changes in an applied load current or applied input voltage.  
         [0014]     Referring now to  FIG. 1 , there is illustrated a basic linear voltage regulator  102 . A linear voltage regulator  102  operates by using a voltage controlled current source  104  to force a fixed voltage to appear at the regulator output node  106 . The sense and control circuitry  108  monitors or senses the output voltage at node  106 , and adjusts the current source  104  using a control voltage V C  to hold the output voltage at the desired value. The design limit of the current source defines the maximum load current the regulator can provide and still maintain voltage regulation.  
         [0015]     The voltage regulator  102  has two limitations when operating as an internal voltage regulator. An internal voltage regulator provides voltage regulation wherein the current source  104  resides within the voltage regulation device. For an external voltage regulator, the current source  104  will be located somewhere outside of the voltage regulation device. The maximum output current (I MAX ) of the current source  104  can be limited due to the area on the chip used by the current source  104 . Thus, if additional current is needed once the internal voltage regulator is providing a maximum current value enabled by its area, this is not possible. Internal voltage regulators may further be limited by thermal limitations required to dissipate energy generated by the current source  104 . In the situation where the input voltage V IN  varies from 3 V-20 V, the voltage regulator  102  may exceed the particular thermal limits for the internal linear voltage regulator  102  at the higher voltage levels. For example, if the input voltage equals 20 V, the output voltage V OUT  equals 5.5 V and the current provided through load  110  will equal 100 mA. The power provided by the current source  104  equals 1.45 watts. It would be difficult for an internal linear voltage regulator  102  to dissipate this much power. Thus, there is a need to provide a user with the flexibility to utilize an external device instead of an internal linear voltage regulator in order to move power dissipation off of the chip to prevent an internal linear voltage regulator from exceeding its current limits and to provide additional current when an area of an internal regulator limits further current increases.  
         [0016]     The circuitry for implementing a configurable internal/external linear voltage regulator is illustrated in  FIG. 2 . The configurable internal/external linear voltage regulator  200  contains three circuit blocks including a band-gap generator  202 , an internal pass linear voltage regulator  204  and a differential amplifier sub-block  206  used for an external pass linear voltage regulator. The band-gap generator  202  provides a reference band-gap voltage and reference currents via a number of pin outputs. Three pin inputs BG_T 0 , BG_T 1  and BG_T 2  provide trim bit inputs via lines  205  to trim the band-gap voltage provided by the band-gap generator  202 . The band-gap generator  202  is connected to the system power bus via a pin VCC 30  that is connected to the power bus  208  via line  209 . Pin VCC_INT of the band-gap generator  202  provides a reference voltage vddi via line  210 . A band-gap reference voltage is provided from pin VBG over line  212 . Additionally, the band-gap generator provides a number of reference currents via lines  213  from pin outputs P 2   p   5   b , P 2   p   5   a  and P 100 . Output pin VSS of the band-gap generator  202  is connected to the system ground GNDA. Output pin PRNG of the band-gap generator  202  is connected to input line prng  211  and is connected to ground through resistor  213 .  
         [0017]     The internal voltage regulator  204  provides internal voltage regulation in the manner described above with respect to  FIG. 1 . The VIN pin of the internal voltage regulator  204  is connected directly to the power bus  208 . The VBG pin is connected to receive the band-gap reference voltage from the band-gap generator  202  via line  212 . The N 2  pin of the internal voltage regulator  204  is connected to the N 2 P 5  pin of the band-gap generator  202  via line  205 . The VSS pin is connected to ground via line  207 . The regulated output voltage of the internal voltage regulator  204  is provided through pin VCC_OUT over power bus  214 . The internal voltage regulator  204  is enabled and disabled via pin EN connected to line  209 .  
         [0018]     The differential amplifier sub-block  206  for an external linear voltage regulator is connected to lines  205  to receive the three reference currents from the band-gap generator  202  at pin inputs IP 1 , IP 2  and IP 3 . Additionally, the differential amplifier  206  sub-block is connected to line  212  to receive the band-gap reference voltage at pin Vbg. The VCC and enable (EN) pins of the differential amplifier  206  are connected to vddi. The prng pin is connected the prng input via line  211 , and pin VSS is connected to line  207  and the ground input. The output of the differential amplifier sub-block  206  is connected to the regulated voltage output line  214 . The LINDRV pin is used to enable and disable the internal linear voltage regulator  204  by selectively grounding the pin when use of the internal linear voltage regulator  204  is desired. When the LINDRV pin is grounded, an enable output is applied from the EX_OFF pin via line  209  to the EN input of the internal linear voltage regulator  204  that enables the internal linear voltage regulator such that the internal linear voltage regulator regulates the input voltage applied via the input bus  208  and provides an output of the regulated voltage over line  214 . When the LNDRV pin is not grounded, the differential amplifier sub-block  206  acts as an amplifier output for an external linear voltage regulator element. A user might select the use of an external linear voltage regulator element to reduce thermal dissipation that is required to occur upon the integrated circuit containing the internal linear voltage regulator element. In high voltage applications, the internal linear voltage regulator would be required to dissipate close to 1.5 watts of power as discussed previously with respect to  FIG. 1 . By disabling the internal linear voltage regulator source and attaching an external linear voltage regulator source via differential amplifier sub-block  206 , an external linear voltage regulator including a heat sink may be connected to the circuit for dissipating power at these levels off of the chip rather than on the chip.  
         [0019]     The LINDRV pin should be connected to ground when using an external 5 V power supply or when using the internal linear regulator. Referring now to  FIGS. 3   a  and  3   b , when using an external linear regulator, the LINDRV pin is connected to the gate of a PMOS device  302 , and a resistor  304  should be connected between the gate and source of the PMOS device  302 . Alternatively, a PNP device  306  can be used instead of a PMOS device  302 . In this case, the LINDRV pin should be connected to the base of the PNP device  306 . The PNP device illustrated in  FIG. 3   b  is turned on by current. The PMOS device  302  illustrated in  FIG. 3   a  is turned on by voltage. Thus, a current output must be provided from the LINDRV pin of the differential amplifier sub-block  206 . This provides the user with the ability to compensate for the provided current and the user may convert the current to a voltage by using a resistor.  
         [0020]     Referring now to  FIG. 4 , there is illustrated one example of the circuitry which may be implemented within the differential amplifier sub-block  206 . In this case, a single stage amplifier is illustrated. The amplifier consists of a transistor  402  having its drain/source path connected between V+ and node  404 . The gate of the transistor  402  is connected to an input  403 . Transistor  406  is connected between node  404  and node  416 . The gate of transistor  406  is connected to input line  408 . Transistor  410  has its drain/source path connected between nodes  404  and  411 . The gate of transistor  410  is connected to input line  412 . Transistor  414  has its drain/source path connected between node  416  and ground. The gate of transistor  414  is also connected to node  416 . Transistor  418  has its drain/source path connected between node  411  and ground. The gate of transistor  418  is connected to the gate of transistor  420 . Transistor  420  has its drain/source path connected between node  422  and ground. Node  422  is connected to the pin LINDRV. Transistor  424  has its drain/source path connected between node  426  and node  422 . The gate of transistor  424  is connected to the gate of transistor  426 . Additionally, the drain/source path oftransistor  426  is connected between node  427  and ground through a resistor  430 . Additionally, the gate of transistors  426  and  424  are connected to node  427 . A current source I 2    431  resides between V+ and node  426 . A second current source I 3    428  resides between V+ and node  427 . Node  426  is also connected to the input of inverter  432 . The output of inverter  432  provides a detect signal that is applied to output pin EX_OFF of the differential amplifier sub-block  206  to enable or disable the internal linear voltage regulator  204 . When the LINDRV pin connected to node  422  is grounded, transistor  424  will be on and can overcome current  12  causing the output of inverter  432  to be logically high. This logical high signal is used to enable the internal linear voltage regulator  204 .  
         [0021]     Referring now to  FIG. 5 , there is illustrated a voltage regulator configured to operate as an internal linear voltage regulator according to the present disclosure. The VIN pin  502  is connected to PVCC which may be varied anywhere from 3.3 V to 20 V with a two ohm internal series linear regulator  504 , which is internally compensated. The external series linear regulator option is used for applications requiring pass elements of less than two ohms. When using the internal regulator  504 , the LIN_DRV pin  506  is connected directly to GND. The PVCC and VIN pins include bypass capacitors,  508  and  510 , respectively, connected to ground for buffer operation. The input (VIN) ofinternal series linear regulator  504  can range from 3.3 V to 20 V. The internal linear regulator  504  provides power for internal MOSFET drivers through the PVCC pin  512  and to the analog circuitry through the VCC pin  514 . The VCC pin  514  is connected to the PVCC pin  512  via an RC filter to prevent high frequency driver switching noise from entering the analog circuitry. The RC filter consists of resistor  516  connected between the VCC and PVCC pins and capacitor  518  connected between pin VCC  514  and ground. When the VIN pin  502  drops below 5.6 volts, the pass element will saturate, PVCC  512  will track VIN, minus the drop out of the linear regulator: PVCC=VIN−2·I VIN . When used with an external 5 V supply, the VIN pin should be tied directly to the PVCC pin.  
         [0022]     Referring now to  FIG. 6 , there is illustrated a voltage regulator operating using an external linear regulator. The LIN_DRV pin  506  provides the syncing drive capability for an external pass element linear regulator controller. The external linear operations are especially useful when the internal linear dropout is too large for a given application. When using the external linear regulator option, the LIN_DRV pin  506  is connected to the gate of a PMOS device  602 , and a resistor  604  should be connected between its gate and source. A resistor  606  and a capacitor  608  should be connected from gate to drain or gate to source as necessary to compensate the control loop. As discussed herein above, a PNP device can be used instead of a PMOS device, in which case the LIN_DRV pin  506  should be connected to the base of the PNP pass element. The maximum syncing capability of the LIN_DRV pin  506  is 2 mA, and should not be exceeded if using an external resistor for a PMOS device. The VCC pin  514  should be connected to the PVCC pin  512  with an RC filter to prevent high frequency driver switching noise from entering the analog circuitry. The RC filter consists of a resistor  516  and a capacitor  518 .  
         [0023]     By combining an internal pass linear regulator and the option for a user programmable external pass linear regulator utilizing an external PMOS or PNP pass element, a user is able to selectively reduce the thermal dissipation that must be carried out on an integrated circuit. Thus, for a high voltage application, the internal linear regulators would not be required to dissipate close to 1.5 watts of power, but instead may choose to use an external linear regulator with a heat sink. Alternatively, for applications requiring a higher maximum current than can be provided by an internal linear regulator due to size limitations of the device, the ability to choose an external regulator is beneficial. This will provide the ability for the linear regulator to operate over a supply range of 3 V to 20 V.  
         [0024]     Although the preferred embodiment has been described in detail, it should be understood that various changes, substitutions and alterations can be made therein without departing from the spirit and scope of the invention as defined by the appended claims.