Abstract:
A voltage regulator having a device characteristic comprises a first terminal connectable to a first external impedance. A measurement circuit communicates with the first terminal to measure the first external impedance. A control circuit controls the device characteristic as a function of the measured first external impedance.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a divisional of U.S. patent application No. 11/411,377 filed Apr. 26, 2006, which is a divisional of U.S. patent application No. 11/220,255, filed on Sep. 6, 2005, now U.S. Pat. No. 7,062,392, which is a divisional of application No. 10/251,372, filed Sep. 19, 2002, now U.S. Pat. No. 6,970,794, the entire contents of which are herein incorporated by reference. 
     
    
     BACKGROUND  
       [0002]     Broad classes of semiconductor devices may include several configurations of the same basic device differing in one or more aspects such as output voltage, frequency, trigger temperature, and the like. There are several conventional techniques for providing a specific configuration from a family of devices. In one technique, different versions of the same basic semiconductor are manufactured with slightly different internal component values or configuration to provide the differing outputs. For example, voltage regulators may include a family of devices having various output voltages and tolerance levels. Different devices are manufactured and inventoried by suppliers etc. to provide each of the possible combinations of output voltage and tolerance. An advantage of this approach is that devices with tight tolerances may be provided without the need for expensive external components. However, the cost of the regulators may be higher due to the lower quantities that are produced for each specific voltage/tolerance combination as well as the increased inventory costs.  
         [0003]     Another technique uses one or more external components to complete an internal circuit such as an error amplifier for a voltage regulator. Here, the tolerance of the external components has a direct affect on the tolerance of the output that is generated. To attain an output with a tight tolerance, higher priced tight tolerance external components may be required. In addition, a large selection of the tight tolerance external components may be have to be stocked to provide flexibility in setting the output to the desired value.  
         [0004]     Shown in  FIG. 1A  is a third technique for configuring a semiconductor  5 . The third technique uses digital input signals to set the semiconductor configuration. Pull-up resistors  6  in combination with switches  7  generate the digital input signals. One digital input may select between two ( 21 ) configurations. Two digital inputs may select between four ( 22 ) configurations. Three digital inputs may select between eight ( 23 ) configurations and so on. To select between a moderate number of configurations, a large quantity of pins may be required. Dedicating four pins merely for selecting between 16 configurations is costly in terms of both, price and package size. Whereas, using two pins for selection may provide reasonable cost and package size, but only provides selection from amongst four configurations.  
       SUMMARY  
       [0005]     A voltage regulator has a plurality of predetermined configurations and comprises a measurement circuit to measure an electrical characteristic of at least one external impedance and to determine a digital value corresponding to the measured electrical characteristic. An address generator converts the digital value to a first digital address corresponding to a memory location having contents. Each of the contents corresponds to a respective one of the predetermined configurations. A controller configures the voltage regulator based on the contents of the memory location corresponding to the first digital address.  
         [0006]     The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
     
    
     DESCRIPTION OF DRAWINGS  
       [0007]      FIG. 1A  is a block diagram of a selection circuit connected to a conventional configurable semiconductor.  
         [0008]      FIG. 1B  is a block diagram of a configurable semiconductor connected to external impedances.  
         [0009]      FIG. 2  is a detailed block diagram of a configurable semiconductor connected to external impedances.  
         [0010]      FIGS. 3A and 3B  are diagrams showing a relationship between an external impedance value and a digital value.  
         [0011]      FIG. 4  is a schematic diagram of a configurable semiconductor having a multifunction pin.  
         [0012]      FIG. 5  is a schematic diagram of a multifunction pin with programmable control.  
         [0013]      FIG. 6  is a schematic diagram of a timing circuit for generating a digital value.  
         [0014]      FIG. 7  shows waveforms associated with the timing circuit of  FIG. 6 .  
         [0015]      FIG. 8  is a flow diagram of an operation for configuring a semiconductor.  
         [0016]      FIG. 9  is a flow diagram of an operation for selecting values for external impedances for configuring a semiconductor.  
         [0017]      FIG. 10A  is a block diagram of a voltage regulator connected to an external impedance.  
         [0018]      FIG. 10B  is a block diagram of a voltage regulator connected to two external impedances. 
     
    
       [0019]     Like reference symbols in the various drawings indicate like elements.  
       DETAILED DESCRIPTION  
       [0020]      FIG. 1B  shows a configurable semiconductor device  10  having, for example, two select pins  12  and  14  to connect to two external impedances  16  and  18 . The configurable semiconductor device  10  advantageously uses a reduced number of select pins for interfacing to external components, as compared to conventional devices, to select one or more output and internal characteristics. One or more pins may be used to interface to the external component(s). The configurable semiconductor device probes or derives information from the external components connected to the select pins. The derived information has three or more predetermined level ranges that correspond to selected levels of the device characteristics. For example, a single pin connected to an external resistor may be used to select any one of 16 output voltage levels. The resistance of the external resistor is preferably selected to be one of 16 predetermined standard values. Each of the 16 values of resistance corresponds to one of the 16 output voltage levels. In addition, low precision passive components are preferably used as the external components to reduce cost and inventory. Each external component may have multiple, N, predetermined nominal values that each correspond to the selection of a predetermined characteristic level. If one pin is used, then N different characteristic levels may be selected. If two pins are used, then N*N different characteristic levels may be selected, and so forth for an increasing number of selection pins. The types of device characteristics that for example may be selected include output voltage, reference voltage, output current, reference current, clock frequency, temperature threshold, and tolerances of each of the device characteristics. For example, the configurable semiconductor device  10  may have a single select pin  12  connected to an external resistor that may have a nominal value selected from a group of 16 predetermined values. Each of the 16 predetermined values has a measured value range which corresponds to one of 16 predetermined output voltage levels possibly ranging from 3.3 volts to 15 volts. Examples of functional devices for which the configurable semiconductor device is particularly suitable include and are not limited to voltage regulators, current regulators, clock circuits, and temperature sensing circuits.  
         [0021]     The external impedances  16  and  18  are preferably resistors, capacitors, or combinations of resistors and capacitors, but may be any component that exhibits predominantly an inductance, resistance, capacitance, or combination thereof. The external impedances  16  and  18  may be connected directly or indirectly from any energy source such as Vdd and ground or any suitable reference to the configurable semiconductor device pins  12  and  14 . For example, the external impedance  16  may be connected through a resistor/transistor network to Vdd and through a capacitor network to the select pin  12 .  
         [0022]     The configurable semiconductor device  10  may determine a predetermined select value corresponding to the measured value of the impedance connected to a select pin. Preferably, the impedance is selected to have a standard value such as nominal resistance values corresponding to resistors having a 10% tolerance (e.g. 470, 560, 680, . . . ) to reduce device and inventory costs. To account for measurement tolerances and the tolerance of the external impedance, a range of impedance values may correspond to a single select value. The select value is preferably a digital value, but may also be an analog value. For example, values of measured resistance from 2400 ohms to 3000 ohms may be associated with a digital value corresponding to 2. While values of measured resistance from 3001 ohms to 4700 ohms are associated with a digital value corresponding to 3. The measured resistance includes variations due to tolerances of the external impedance and the internal measurement circuit. The impedance measured at each select pin is used to determine a corresponding digital value. The range of digital values may include 3 or more digital values and preferably range from 10 to 16 digital values per select pin. The digital values corresponding to each select pin may be used in combination to describe memory addresses. For example, a device having three select pins each to interface to impedance values that are mapped into one of 10 digital values, may describe 1000 memory addresses or lookup table values. The contents of the memory addresses are used to set a value for an output or internal characteristic of the device. Another exemplary device may include two select pins, each configured to interface to external impedances that are mapped to a digital value within a range of 10 values. The digital values in combination may describe 100 memory addresses or lookup table values that may each contain data for setting a characteristic of the configurable semiconductor device.  
         [0023]      FIG. 2  shows a block diagram of an aspect of a configurable semiconductor device  20 . The configurable semiconductor device  20  includes a select pin  22  to interface to an external impedance  24  that is used for selecting a configuration of the configurable semiconductor device  20 . The external impedance  24  is similar in function and scope to the external impedances  16  and  18 .  
         [0024]     A measurement circuit  26  connected to the select pin  22  measures an electrical characteristic that is a function of the external impedance  24 . For example, a current may be supplied to the external impedance and the voltage that is developed across the external impedance  24  then measured. Also, a voltage may be impressed across the external impedance  24  and then measure the current. Any measurement technique for measuring passive components may be used to measure the electrical characteristic including dynamic as well as static techniques. Exemplary measurement techniques include timing circuits, analog to digital converters (ADCs), and digital to analog converters (DACs). Preferably, the measurement circuit has a high dynamic range. The measurement circuit  26  may generate an output having a value corresponding to the value of the external impedance  24 . The output may be either digital or analog. The same output value preferably represents a range of external impedance values to compensate for value variations such as tolerances in the external impedance value, interconnect losses, and measurement circuit tolerances due to factors including process, temperature, and power. For example, all measured external impedance values ranging from greater than 22 up to 32 ohms may correlate to a digital output value of “0100”. While measured external impedance values ranging from greater than 32 up to 54 ohms may correlate to a digital output value of “0101”. The actual external impedance values are a subset of the measured external impedance value to account for the value variations. For example, in the above cases the actual external impedance values might be from 24 to 30 ohms and from 36 to 50 ohms. In each case an inexpensive low precision resistor may be selected to have a value centered within the range, such as 27 ohms and 43 ohms. In this way, inexpensive low precision components may be used to select amongst a range of high precision outputs. The select value may be used directly as a variable value to control a device characteristic of the configurable semiconductor  20 . The variable value may also be determined indirectly from the select value.  
         [0025]     A storage circuit  27  may include variable values that may be selected as a function of the select value. The storage circuit may be any type of storage structure including content addressable memory, static and dynamic memory, and look-up tables.  
         [0026]     For the case that the measurement circuit  26  generates output values that have a one-to-one correspondence to the external impedance values, a digital value determiner  28  may then set the output value to a select value that corresponds to a range of external impedance values.  
         [0027]      FIG. 3A  shows a relationship between groups of impedance values  50  and associated select values  54 . The groups of impedance values  50  may have a one-to-one correspondence to groups of digital output values  52  which are converted to the select values  54  associated with each of the groups of impedance values  50 . The impedance values ranging from a minimum impedance value to a maximum impedance are separated in into three or more groups, with each group having a nominal impedance. The nominal impedance values of each of the groups may be selected to have a spacing between nominal impedance values. Here, the nominal values, 27 ohms and 43 ohms, of the groups of impedance values have a spacing of 16 ohms. The spacing between the groups of impedance values is preferably based on geometric progression, however any mathematical relationship may be used to establish spacing between the groups such as logarithmic, linear, and exponential. The spacing between impedance groups may be based on any impedance value of the groups including a nominal value, an average value, a mean value, a starting value, and an ending value. Factors that influence selection of the impedance range of the groups and the spacing may include various tolerances such as the tolerance of the external impedance, the tolerance of internal voltage and current sources, and the tolerance of the measurement circuit. The tolerances may for example be caused by process, temperature, and power variations.  
         [0028]      FIG. 3B  shows a relationship between ranges of impedance values  56  and associated select values  58 . The ranges of impedance values  56  have a direct correspondence to the select values  58 . The impedance values ranging from a minimum impedance value to a maximum impedance are separated in into three or more groups, with each group having a nominal impedance. The nominal impedance values of each of the groups may be selected to have a spacing between nominal impedance values. Here, the nominal values, 27 ohms and 43 ohms, of the groups of impedance values have a spacing of 16 ohms. This direct correspondence between the ranges of impedance values  56  and associated select values  58  may be implemented by, for example, a nonlinear analog to digital converter (not shown).  
         [0029]     Referring back to  FIG. 2 , an address generator  30  may determine memory locations corresponding to the digital output values associated with external impedances connected to the select pins. The memory locations may be grouped in any manner such as a list for a single select pin, a lookup table for two select pins, and a third order table for three select pins.  
         [0030]     A controller  32  sets a device characteristic of the configurable semiconductor device  20  as a function of the variable value. The variable value may be generated directly by the measurement circuit, determined indirectly from the select value, and determined from the contents of a memory location corresponding to the external impedance values connected to the select pins.  
         [0031]      FIG. 4  shows an aspect of another configurable semiconductor device  60 . Configurable semiconductor device  60  is similar to configurable semiconductor device  20  in function, except that configurable semiconductor device  60  includes at least one multi-purpose select pin  62 . The multi-purpose select pin  62  may be used for configuring the semiconductor device  60  as well as for an additional function such as power down (PD), power enable, mode selection, reset, and synchronous operation. The semiconductor device  60  may be configured in a manner similar to that of configurable semiconductor device  20 .  
         [0032]     In one aspect, a first range of impedance values connected to the multi-purpose select pin  62  may be used to configure the configurable semiconductor device  60 , while operation of the additional function may be controlled by a voltage or current impressed on the multi-purpose select pin, or impedance values outside the first range of impedance values.  
         [0033]     An external impedance  64  and a switch  66  may be connected to the multi-purpose select pin  62  to provide the selection function and the additional function respectively. Bias voltages, Vb 1  and Vb 2 , may be applied to the external impedance  64  and transistor  66 . The bias voltages, Vb 1  and Vb 2 , may each be any value ranging from negative voltage through ground to positive voltage, and equal or not equal. The switch  66  may be connected in any manner including from the multi-purpose select pin  62  to ground, from the multi-purpose select pin  62  to a voltage source, from the multi-purpose select pin  62  to a current source, and from the multi-purpose select pin  62  through another impedance to an energy source. Any type of switch or device configured as a switch may be used including transistors, analog switches, jumper wires/traces, and manual switches.  
         [0034]      FIG. 5  shows a configurable semiconductor device  70  coupled to a digital control circuit  72 . The digital control circuit  72  may be connected in any manner such as a stand-alone circuit and included in another device such as a processor. The configurable semiconductor device may include a multi-purpose select pin  74  similar in function to configurable semiconductor device  60 . The digital control circuit  72  may include several switches  76  to control external impedances  78  for setting an impedance on the multi-purpose select pin  74 . Any number and type of switches  76  may be employed including transistors, analog switches, jumper wires/traces, and manual switches. Preferably, the external impedances  78  are selected to have standard values although any range of values may be used. Another transistor  80  may control operation of additional functions.  
         [0035]      FIG. 6  shows one embodiment of a measurement circuit  100  for determining a digital output  106  corresponding to an external impedance  102 . The external impedance  102  may be connected to the measurement circuit  100  through a select pin  104 . Table I shows exemplary values for the external impedance  102  and corresponding values of the digital output. Predefined operation # 2  may enable the power down function. The impedance at the select pin that corresponds to predefined operations # 1  or # 2  may be intentional or unintentional such as a selected resistor, a cold solder joint, a broken trace, shorted traces, or a failed external device.  
                                                     TABLE I                                       Digital       #   Rx/Ry   Vout   Vout %   Output                                0   Short to Vss up   0   0   Predefined           to 10k           operation #1       1   19.6k    0.8   −2   000       2   28.5k    1.0   −4   001       3    40k   1.2   −6   010       4    56k   1.5   −8   011       5   80.6k    1.8   +2   100       6   113k   2.5   +4   101       7   160k   3.0   +6   110       8   226k   3.3   +8   111       9   400k to an open           Predefined                       operation #2                    
         [0036]      FIG. 7  shows a timing diagram associated with the measurement circuit  100 . A first waveform  120  represents a clock signal  120  to the D flip-flop  110 . A second waveform  122  represents an input signal to the D input of the flip-flop  110 . In operation, a controlled resistor  112  is initially set to a predetermined value. A first voltage is developed at a first node  114  as a function of the controlled resistor  112  and the external impedance  102 . The first voltage is clocked through the flip-flop  110  by the clock signal  120 . An incrementer/decrementer  116  may convert the output of the flip-flop  110  to the digital output  106 . In response to the digital output  106 , a decoder  118  adjusts the controlled resistor  112  to decrease the first voltage. The counter continues to increment until the first voltage decreases to a level equivalent to a logic “0”.  
         [0037]      FIG. 8  shows an operation of a configurable semiconductor device. Starting at block  150 , energy is supplied to an external impedance. Continuing to block  152 , an electrical characteristic that is a function of the external impedance is measured. Electrical characteristics such as a voltage at the select pin and a current flowing through the select pin may be measured. At block  154 , a select value corresponding to the measured electrical characteristic is determined. Continuing to block  156 , an address may be generated as a function of the digital value. At block  158 , the contents of the address are determined. At block  160 , a variable may be controlled as a function of the select value such as directly and based on the address contents. At block  162 , a device characteristic such as an output voltage may be controlled as a function of the variable.  
         [0038]      FIG. 9  shows an operation for selecting the spacing of external impedances used for configuring a semiconductor device. The spacing is preferably selected to permit the use of low precision components by varying the spacing from lower values to higher values to account for potential variations associated with the measurement circuit. Starting at block  200 , a measurement circuit is provided. Continuing to blocks  202  and  203 , tolerances associated with the measurement circuit and the external impedances may be determined. The tolerances may include variations due to process, temperature, and power. At block  204 , a measurement error such as a geometric progression, a maximum error, and root of the sum of the squares (RSS) error may be computed. Continuing to block  206 , a quantity of discrete values for the external impedance may be determined. For example, the measurement error may be applied across a voltage range of the measurement circuit to determine the maximum number of discrete values that may be selected. The quantity of discrete values may be any integer value greater than one. At block  208 , nominal values are selected for the external impedance as a function of the computed error and the selected quantity of discrete values. The described operation is not limited to the described order of operation. Other ones of the variables may be solved for such as solving for the tolerance of the external impedance after selecting a desired quantity of discrete values.  
         [0039]      FIG. 10A  is an example of a voltage regulator in accordance with the present invention. Referring now to  FIG. 10A  a voltage regulator  200  is shown therein providing Vout to load  210 , an external impedance  220  is used to select Vout. Table II shows exemplary values for the external impedance  220  and corresponding values of Vout. Predefined operation # 2  may enable the power down function or low voltage to protect for an overvoltage condition presented to load  210 . The impedance at the select pin that corresponds to predefined operations # 1  or # 2  may be intentional or unintentional such as a selected resistor, a cold solder joint, a broken trace, shorted traces, or a failed external device.  
                       TABLE II                       #   Impedance 220   Vout                   0   Short to Vss up   0 or power           to 10k   down       1   19.6k    0.8       2   28.5k    1.0       3    40k   1.2       4    56k   1.5       5   80.6k    1.8       6   113k   2.5       7   160k   3.0       8   226k   3.3       9   400k to an open   0 or low               voltage                    
         [0040]      FIG. 10B  is an example of a voltage regulator in accordance with the present invention. Referring now to  FIG. 10B  a voltage regulator  200  is shown therein providing Vout to load  210 , an external impedance  220  is used to select a nominal Vout and impedance  240  is used to select the offset from the nominal Vout. This provides for a significant number of additional output voltages. Table III shows exemplary values for the external impedance  220  and corresponding values of the offset percentages. If impedance  240  is a large value or perhaps an open circuit no offset will be applied to the nominal Vout. While if impedance  240  is a short or very low a predefined operation, such as discussed above, is implemented.  
                       TABLE III                               Offset       #   Impedance 240   percentage                   0   Short to Vss up   Predefined           to 10k   operation       1   19.6k    −2       2   28.5k    −4       3    40k   −6       4    56k   −8       5   80.6k    +2       6   113k   +4       7   160k   +6       8   226k   +8       9   400k to an open   No Offset                    
         [0041]    
       
         
               
               
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE IV 
               
             
             
               
                   
               
               
                   
               
               
                   
                   
                   
                 Short to 
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                   
                   
                   
                 Vss up 
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                   
                   
                   
                 to 10k 
                 19.6k 
                 28.5k 
                 40k 
                 56k 
                 80.6k 
                 113k 
                 160k 
                 226k 
                 400k to 
               
             
          
           
               
                 Imped 
                 Imped 
                 Nominal 
                 Offset % 
                 an 
               
             
          
           
               
                 240 
                 220 
                 Vout 
                 0 
                 −2 
                 −4 
                 −6 
                 −8 
                 +2 
                 +4 
                 +6 
                 +8 
                 open 
               
               
                   
               
               
                 Short 
                 0 or 
                 0 or 
                 0 or 
                 0 or 
                 0 or 
                 0 or 
                 0 or 
                 0 or 
                 0 or 
                 0 or 
                 0 or 
                 0 or 
               
               
                 toVss 
                 power 
                 power 
                 power 
                 power 
                 power 
                 power 
                 power 
                 power 
                 power 
                 power 
                 power 
                 power 
               
               
                 up to 
                 down 
                 down 
                 down 
                 down 
                 down 
                 down 
                 down 
                 down 
                 down 
                 down 
                 down 
                 down 
               
               
                 10k 
               
               
                 19.6k  
                 0.8 
                 0.8 
                 * 
                 0.784 
                 0.768 
                 0.752 
                 0.736 
                 0.816 
                 0.832 
                 0.848 
                 .0864 
                 0.8 
               
               
                 28.5k  
                 1.0 
                 1.0 
                 * 
                 0.980 
                 0.960 
                 0.940 
                 0.920 
                 1.020 
                 1.040 
                 1.060 
                 1.080 
                 1.0 
               
               
                  40k 
                 1.2 
                 1.2 
                 * 
                 1.176 
                 1.152 
                 1.128 
                 1.104 
                 1.224 
                 1.248 
                 1.272 
                 1.296 
                 1.2 
               
               
                  56k 
                 1.5 
                 1.5 
                 * 
                 1.470 
                 1.440 
                 1.410 
                 1.380 
                 1.530 
                 1.560 
                 1.590 
                 1.620 
                 1.5 
               
               
                 80.6k  
                 1.8 
                 1.8 
                 * 
                 1.764 
                 1.728 
                 1.692 
                 1.656 
                 1.836 
                 1.872 
                 1.908 
                 1.944 
                 1.8 
               
               
                 113k 
                 2.5 
                 2.5 
                 * 
                 2.450 
                 2.400 
                 2.350 
                 2.300 
                 2.550 
                 2.600 
                 2.650 
                 2.700 
                 2.5 
               
               
                 160k 
                 3.0 
                 3.0 
                 * 
                 2.940 
                 2.880 
                 2.820 
                 2.760 
                 3.060 
                 3.120 
                 3.180 
                 3.240 
                 3.0 
               
               
                 226k 
                 3.3 
                 3.3 
                 * 
                 3.234 
                 3.168 
                 3.102 
                 3.036 
                 3.366 
                 3.432 
                 3.498 
                 3.564 
                 3.3 
               
               
                 400k 
                 0 or 
                 0 or 
                 0 or 
                 0 or 
                 0 or 
                 0 or 
                 0 or 
                 0 or 
                 0 or 
                 0 or 
                 0 or 
                 0 or 
               
               
                 to an 
                 low 
                 low 
                 low 
                 low 
                 low 
                 low 
                 low 
                 low 
                 low 
                 low 
                 low 
                 low 
               
               
                 open 
                 voltage 
                 voltage 
                 voltage 
                 voltage 
                 voltage 
                 voltage 
                 voltage 
                 voltage 
                 voltage 
                 voltage 
                 voltage 
                 voltage 
               
               
                   
               
               
                   * predefined operation    
               
             
          
         
       
     
         [0042]     Table IV above is an example of the nominal Vout and the offset percentage selected in accordance with external impedances. For example if impedance  220  is nominally 160 k ohms the nominal Vout is 3.0 volts and if impedance  240  is 28.5 k the offset from the nominal Vout is −4%. This results in a Vout of the voltage regulator of 3.168 volts.  
         [0043]     A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.