Patent Publication Number: US-7715157-B2

Title: Semiconductor device and trimming method of the same

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a semiconductor device and a trimming method of the same, and more particularly, to a semiconductor device having a trimming circuit capable of reducing the number of external terminals required for trimming some parts of the semiconductor device and a trimming method of the same. 
   2. Description of the Related Art 
   Generally, in the manufacturing process of semiconductor devices, characteristics of the semiconductor devices may vary due to the variations of parts in the circuits caused by the variation of the manufacturing process. Because of this feature of a semiconductor device, a trimming method is conventionally used to maintain the characteristics especially when the characteristics are required to be highly accurate. 
   As an example of a conventional semiconductor device,  FIG. 3  shows a schematic circuit diagram of a conventional semiconductor device  1  that includes an auxiliary voltage regulator circuit  10  and a voltage regulator circuit  20 . 
   The auxiliary voltage regulator circuit  10  includes a comparator  11  and outputs an output voltage Vs to supply power to an internal circuit (not shown) and a reference voltage circuit  22  of the voltage regulator circuit  20 . The auxiliary voltage regulator circuit  10  further includes a resistor R 1  as a first trimming unit so as to adjust the output voltage Vs. The comparator  11  operates such that a divided voltage divided from the output voltage Vs by the resistor R 1  and a resistor R 2  is equal to a reference voltage Vr 1  applied to the comparator  11 . Further, a test terminal T 1  is provided as an external terminal of the semiconductor device  1  for performing a first trimming adjustment. The voltage regulator circuit  20  includes a comparator  21 , the reference voltage circuit  22 , and an overheat protection circuit  23  and outputs an output voltage Vo. The comparator  21  operates such that a divided voltage divided from the output voltage Vo by resistors R 3  and R 4  is equal to a prescribed reference voltage Vr 2  output from the reference voltage circuit  22 . Further, a test terminal T 2  extending from the overheat protection circuit  23  is provided as another external terminal. A detailed description of the overheat protection circuit as well as the connection with the test terminal T 2  is provided below with reference to  FIG. 4 . 
     FIG. 4  is a schematic circuit diagram of the overheat protection circuit  23  in  FIG. 3 . As shown in  FIG. 4 , the overheat protection circuit  23  includes a reference voltage source  25  generating a reference voltage Vr 3 , a temperature detection diode D 1 , a constant current source I 1 , and a comparator  24 . The reference voltage source  25  outputting an adjustable reference voltage Vr 3  is provided as a second trimming unit so as to set a temperature at which the overheat protection circuit  23  is activated. The test terminal T 2  for performing a second trimming adjustment is provided as an external terminal of the semiconductor device  1 . 
   To perform the first trimming adjustment to adjust the output voltage Vs output from the auxiliary voltage regulator  10 , the voltage at the test terminal T 1  is measured. Then, a trimming is performed with respect to the resistor R 1  of the first trimming unit based on the measured voltage. 
   To perform the second trimming adjustment to adjust the temperature at which the overheat protection circuit  23  is activated, a voltage applied to the test terminal T 2  is gradually changed to detect a voltage at which the overheat protection circuit  23  is activated. The detected voltage is adjusted by a trimming voltage determined based on the difference between the chip temperature of the semiconductor device when this test is performed and the chip temperature at which the overheat protection circuit is to be activated. Then the reference voltage Vr 3  of the second trimming unit is adjusted so as to be equal to the adjusted voltage. 
   Unfortunately, as described above, in a conventional trimming method, each test terminal constituting an external terminal is always necessary for the corresponding trimming portion of the semiconductor device. 
   To solve the problem, a method reducing the number of terminals used for trimming is disclosed in, for example, Japanese Patent Application Publication No. H08-204582. According to the Patent Document, the number of terminal is reduced by providing a decoder and data from a trimming circuit is decoded by the decoder and then output from an external terminal. This method may be advantageously employed when there are many trimming portions in the semiconductor device, but may be disadvantageous particularly when there are only a few trimming portions in the semiconductor device. Namely, when this method is employed in small-scale semiconductor devices, the circuit scales may be rather increased due to the additional control circuit including the decoder and control terminals connected from the control circuit. Therefore, this trimming method may not fit a small-scale semiconductor device. 
   Generally and unfortunately, in a semiconductor device, when the number of external terminals increases, the area of the semiconductor chip accordingly increases and the cost is also increased. Especially, the smaller the area of the semiconductor chip is, the more strongly is the semiconductor chip affected by the increase of the external terminals. In addition, the number of the external terminals is a major factor in determining the package size of the semiconductor device. Namely, when the number of the external terminals increases, the package size becomes larger accordingly and the cost is also increased. Further disadvantageously, a larger area for mounting parts becomes necessary and as a result, the size of a system using the semiconductor device may be increased. 
   SUMMARY OF THE INVENTION 
   The present invention is made in light of the above problems and may provide a small-scale semiconductor device having several trimming portions and a trimming method of the same in which trimming can be performed without increasing the number of test terminals in proportion to the number of trimming portions. 
   According to one aspect of the present invention, there is provided a semiconductor device including an auxiliary voltage regulator circuit, provided in the semiconductor device, outputting an output voltage to supply power to an internal circuit of the semiconductor device, where the auxiliary voltage regulator circuit includes a first trimming unit for adjusting the output voltage output from the auxiliary voltage regulator circuit to the internal circuit; an auxiliary circuit comparing a first voltage with a second voltage and performing a prescribed operation based on the comparison result, where the first voltage is in proportion to the output voltage of the auxiliary voltage regulator circuit, and the second voltage is generated by a detecting unit, the auxiliary circuit including a second trimming unit for adjusting the first voltage; and a single test terminal, connected to receive any one of the first voltage and the second voltage, provided as an external terminal of the semiconductor device so as to adjust the first and the second trimming units. 
   According to another aspect of the present invention, there is provided a semiconductor device further including a voltage regulator circuit, in which the auxiliary circuit is an overheat protection circuit detecting the temperature of a semiconductor chip of the semiconductor device and cutting off an output current of the voltage regulator circuit when the temperature exceeds a prescribed temperature. 
   According to still another aspect of the present invention, there is provided a method of trimming a semiconductor device, where the semiconductor device includes an auxiliary voltage regulator circuit, provided in the semiconductor device, outputting an output voltage to supply power to an internal circuit of the semiconductor device; an auxiliary circuit comparing a first voltage with a second voltage and performing a prescribed operation based on the comparison result, the first voltage being in proportion to the output voltage of the auxiliary voltage regulator circuit, the second voltage being generated by a detecting unit in the auxiliary circuit; and a single test terminal; the method of trimming including in order the steps of trimming a first trimming unit using the single test terminal to adjust the output voltage output from the auxiliary voltage regulator circuit to the internal circuit, and trimming a second trimming unit using the single test terminal to adjust the first voltage of the auxiliary circuit. 
   According to an embodiment of the present invention, when a semiconductor device includes an auxiliary voltage regulator circuit and an auxiliary circuit, the auxiliary circuit to be trimmed being driven by a voltage V 1  in proportion to an output voltage Vs of the auxiliary voltage regulator circuit, both an output voltage Vs can be adjusted and the auxiliary circuit can be trimmed by measuring the voltage V 1  using a single external terminal without additional external terminals. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic circuit diagram of a semiconductor device according to an embodiment of the present invention; 
       FIGS. 2A and 2B  are detailed circuit diagrams of the overheat protection circuit of a semiconductor device according to an embodiment of the present invention in  FIG. 1 ; 
       FIG. 3  is a schematic circuit diagram of a conventional semiconductor device including an auxiliary voltage regulator circuit and a voltage regulator circuit; and 
       FIG. 4  is a detailed circuit diagram of the overheat protection circuit of the conventional semiconductor device in  FIG. 3 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In the following, embodiments of the present invention are described in detail with reference to the accompanying drawings. 
     FIG. 1  is a schematic circuit diagram showing a semiconductor device according to an embodiment of the present invention. 
   Similar to  FIG. 3 , the semiconductor device  1  includes an auxiliary voltage regulator circuit  10  and a voltage regulator circuit  20 . The auxiliary voltage regulator circuit  10  includes a reference voltage source  15  generating a reference voltage Vr 1 , a comparator  11 , an output transistor M 1 , and resistors R 1  and R 2  for detecting an output voltage Vs of the auxiliary voltage regulator circuit  10 . The output voltage Vs output from the auxiliary voltage regulator circuit  10  is applied to an internal circuit (not shown) of the semiconductor device  1 , and a reference voltage circuit  22  and an overheat protection circuit  23  of the voltage regulator circuit  20  to supply power to the circuits. As a first trimming unit to adjust the output voltage Vs, the variable resistor R 1  is provided for detecting the output voltage Vs. 
   The voltage regulator circuit  20  includes a comparator  21 , an output transistor M 2 , the overheat protection circuit  23 , and resistors R 3  and R 4 . 
     FIGS. 2A and 2B  are detailed circuit diagrams of the overheat protection circuit  23  in  FIG. 1 . The overheat protection circuit  23  includes resistors R 5  and R 6  for dividing the output voltage Vs output from the auxiliary voltage regulator circuit  10  and generating a first voltage V 1 , a temperature detection diode D 1  for detecting the temperature of a semiconductor chip of the semiconductor device  1 , a constant current source  11  providing a constant current to the diode D 1 , and a comparator  24  comparing the first voltage V 1  with a second voltage V 2  applied between the terminals of the diode D 1 . 
   It should be noted that the configurations of the circuits of  FIGS. 2A and 2B  are the same except that a test terminal T 1  is connected to the conjunction of the resistors R 5  and R 6  in  FIG. 2A  but the test terminal T 1  is connected to the anode of the diode D 1  having the second voltage V 2  in  FIG. 2B . 
   Next, a method of trimming is described. According to an embodiment of the present invention, trimming is performed in the order of adjusting the output voltage Vs of the auxiliary voltage regulator circuit  10  and then adjusting the overheat protection circuit  23 . 
   When trimming is performed with respect to a semiconductor device having the overheat protection circuit in  FIG. 2A , the voltage V 1  is first measured using the test terminal T 1 . Since the resistance values of the resistors R 5  and R 6  are given, the output voltage Vs output from the auxiliary voltage regulator circuit  10  is obtained by the following formula (1):
 
 Vs=V 1*( R 5+ R 6)/ R 6  (1)
 
   In a semiconductor device, it is known that, when the resistances of the resistors R 5  and R 6  vary due to the variation of the manufacturing process, since both resistors suffer the same variation, the resistance ratio of resistor R 5  to resistor R 6  is substantially unchanged. 
   When the resistances of the both resistors R 5  and R 6  vary in the same ratio “α”, the output voltage Vs output from the auxiliary voltage regulator circuit  10  is obtained by the following formula (2): 
   
     
       
         
           
             
               
                 
                   
                     
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                                 R 
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                                 5 
                               
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                                 6 
                               
                             
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   Since the formula (2) is exactly the same as the formula (1), the first voltage V 1  is found to be independent of the variation of a manufacturing process. 
   By using this feature, the output voltage Vs of the auxiliary voltage regulator circuit  10  can be accurately obtained by measuring the voltage V 1  using the test terminal T 1 . Based on the measured voltage V 1 , the resistance of the resistors R 1  to be trimmed can be calculated. As a result, the output voltage Vs can be adjusted by performing the first trimming based on the calculated resistance to be trimmed. 
   Next, the trimming of the overheat protection circuit  23  is performed. First, a voltage applied to the test terminal T 1  is gradually increased to detect an applied voltage at which the overheat protection circuit  23  is activated. 
   Since the temperature characteristics of the voltage Vf between the terminals of the temperature detection diode D 1  are known, a setting voltage of the test terminal T 1  is calculated based on the temperature difference between a temperature when the above test is performed and a temperature when the overheat protection circuit  23  is to be activated. Then, trimming of the resistor R 5  of the second trimming unit is performed such that the first voltage V 1  is substantially equal to the calculated setting voltage of the test terminal T 1 . 
   Namely, the first voltage V 1  after trimming is expressed by in the following formula (3):
 
 V 1 =V 1 a +γ*( Ts−Ta )  (3)
 
   Where:
         Ta: chip temperature when the test is performed   Ts: chip temperature at which the overheat protection circuit is to be activated   γ: temperature coefficient of the voltage Vf between the terminals of the temperature detection diode D 1     V 1   a : the first voltage at which the overheat protection circuit is activated when the test is performed       

   When trimming is performed with respect to a semiconductor device having the overheat protection circuit in  FIG. 2B , voltage applied to the test terminal T 1  using test equipment is gradually changed to detect the second voltage V 2  at which the overheat protection circuit  23  is activated. Since the second voltage V 2  is substantially equal to the first voltage V 1 , trimming is performed the same as the case where the overheat protection circuit in  FIG. 2A  is used to adjust the output voltage Vs output from the auxiliary voltage regulator circuit  10 . 
   Next, the trimming of the overheat protection circuit  23  is performed. In the same manner as the case of the overheat protection circuit in  FIG. 2A , a voltage applied to the test terminal T 1  is gradually increased to detect an applied voltage at which the overheat protection circuit  23  is activated. 
   Since the detected voltage is the first voltage after the trimming is performed, in the same manner as the case of the overheat protection circuit in  FIG. 2A , a setting voltage of the test terminal T 1  is calculated based on the temperature difference between a temperature when the above test is performed and a temperature when the overheat protection circuit  23  is to be activated. Then, trimming is performed on the resistor R 5  of the second trimming unit to adjust the first V 1  voltage so as to be substantially equal to the calculated setting voltage of the test terminal T 1 . 
   The present invention is not limited to the above-mentioned embodiments, and variations and modifications may be made without departing from the scope of the present invention. 
   For example, in the above-mentioned embodiment, an overheat protection circuit is provided as the auxiliary circuit. However, it should be noted that the auxiliary circuit according to an embodiment of the present invention is not limited to the overheat protection circuit, and other circuits such as an over-current protection circuit are also explicitly included in the auxiliary circuit. 
   The present application is based on and claims the benefit of priority of Japanese Patent Application No. 2007-032940, filed on Feb. 14, 2007, the entire contents of which are hereby incorporated by reference.