Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Amplitude control
Reexamination Certificate
2001-07-19
2002-12-17
Callahan, Timothy P. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Amplitude control
C327S327000, C327S332000, C327S108000, C327S538000
Reexamination Certificate
active
06496049
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a semiconductor integrated circuit. More specifically, the present invention is directed to a technique effectively adaptable to a power MOS transistor having a current control function such as an overcurrent protection. For example, the present invention is directed to such a technique advantageously adaptable to either a power MOS transistor equipped with a composite function or a semiconductor switch having a composite function.
2. Description of the Related Art
Power MOS transistors have been widely used as, for example, power switches interposed between power sources and loads, capable of ON/OFF-controlling currents flowing therethrough. Conventionally, semiconductor integrated circuits have been provided on which such a power MOS transistor is formed on the same semiconductor substrate in combination with current control circuits capable of protecting overcurrents. This type of semiconductor integrated circuit is also referred to as an MOS transistor equipped with a composite function or a semiconductor switch having a composite function. For instance, when this semiconductor integrated circuit is used, both a conventional mechanical contact type switch function and a fuse (or overcurrent breaker) function may be collected into a single element, and also may be replaced by this semiconductor integrated circuit.
In order to provide user-friendly operation of this semiconductor integrated circuit in such a case that, for example, this semiconductor integrated circuit is employed as a replacement component of a conventional mechanical contact type switch, or in order to provide user-friendly operation as a single body of a power MOS transistor, this semiconductor integrated circuit is constructed in such a manner that only limited numbers of external terminals thereof are provided with respect to users. Concretely speaking, this semiconductor integrated circuit owns three terminals as external terminals (user terminals), namely, an output terminal, a control terminal, and a common terminal. When the respective terminals of the semiconductor integrated circuit are defined in correspondence with electrodes of a single body of an MOS transistor, the output terminal corresponds to the drain of this MOS transistor, the common terminal corresponds to the source thereof, and the control terminal corresponds to the gate thereof. A user connects both the output terminal and the common terminal in series to a current supply path between the power supply and the load, and also applies a control voltage between the control terminal and the common terminal, so that the user may turn ON/OFF the above-explained current supply path.
Generally speaking, an overcurrent protection circuit is employed as the current control circuit formed on the above-described semiconductor integrated circuit. As represented in
FIG. 11
, this overcurrent protection circuit is arranged by a current detecting circuit
10
, a reference voltage generating circuit
20
, a comparing circuit
30
, and a gate control circuit
40
. The current detecting circuit
10
converts a load current flowing between an output terminal P
1
and a common terminal P
3
into a corresponding voltage so as to detect this load current. The reference voltage generating circuit
20
generates a predetermined reference voltage. The comparing circuit
30
compares the current-detecting voltage of the current detecting circuit with the reference voltage. The gate control circuit
40
controls a gate voltage of a power MOS transistor based upon the comparison output of the comparing circuit
30
.
In this case, in the above-explained current detecting circuit
10
, a voltage dividing resistor element (shunt resistor) is provided in a current supply path of the load current, namely between the output terminal and the common terminal in such a manner that this voltage dividing resistor element is connected in series to a channel of an MOS transistor Q
1
so as to convert the above-described load current into the voltage for detection purposes. Then, a current-detecting voltage is obtained from both ends of this voltage dividing resistor element.
As a result, between the output terminal and the common terminal of the above-explained semiconductor integrated circuit, an internal resistance may appear which is obtained by adding an ON-resistance (channel resistance) of the power MOS transistor to the resistance value of the voltage dividing resistor element. However, since this internal resistance may cause a voltage loss in the load current supply circuit, the resistance value of this internal resistance should be made lower as being permitted as possible. Very recently, while ON resistances of power MOS transistors could be reduced on the order of several milli-ohms, a major portion of this internal resistance could occupy the resistance value of the above-described voltage-dividing resistor element. In order that the current control operation such as the overcurrent protection is carried out while this internal resistance is made lower as being permitted as possible, the above-explained reference voltage must be set to a low voltage.
As to the reference voltage generating circuit, for instance, as shown as a reference in
FIG. 12
, such a circuit using a zener diode Dz is usually employed. Normally, the reference voltage (zener voltage) obtained from the zener diode Dz is higher than, or equal to approximately 6V, and therefore, this zener voltage cannot be directly used as the above-explained reference voltage. As a consequence, as shown in
FIG. 12
, this zener voltage of the zener diode is subdivided by using resistance elements R
11
and R
12
so as to obtain a predetermined lower reference voltage. There is one method for using a forward direction voltage of a diode which is lower than a zener voltage. However, since this forward direction voltage is equal to approximately 0.5V to 1V, this forward direction voltage is sub-divided by a resistor in the case that a reference voltage lower than this forward direction voltage is required.
However, the Inventors of the present invention could find out such a fact that the above-described techniques own the below-mentioned problems.
That is, since either the zener voltage of the zener diode or the forward direction voltage of the diode owns the large temperature dependent characteristic, there is such a problem that the stable reference voltage could not be obtained, and this stable reference voltage is required in order to correctly perform the current control operation such as overcurrent protections. This temperature dependent characteristic may be canceled by using, for example, such a temperature compensation realized by a band gap circuit. However, such a temperature compensation method may cause another problem that the band gap circuit becomes complex. However, there is a further serious problem. That is, in the above-described semiconductor integrated circuit equipped with the current control circuit, this semiconductor integrated circuit is made of such a circuit format that the operation voltages of the reference voltage generating circuit and of the comparing circuit may depend upon the control voltage for ON/OFF operations which is applied between the control terminal and the common terminal, the following restriction may exit. That is, the necessary reference voltage must be produced within the range of this control voltage.
In order to realize such a user-friendly operation as either the MOS transistor equipped with the composite function or the semiconductor switch having the composite function, this control voltage could not be obtained such a high voltage. To the contrary, this control voltage should be desirably made lower as being permitted as possible. When these aspects are considered, there is another problem. That is, in the reference voltage generating circuit shown in
FIG. 12
using either the zener voltage of the zener diode or the forward direction voltage of the diode,
Fujiki Atsushi
Nakasu Masatoshi
Ohsawa Kazuaki
Tsukagoshi Nobuo
Callahan Timothy P.
Hitachi , Ltd.
Mattingly Stanger & Malur, P.C.
Nguyen Hai L.
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