Patent Application
20080036436
Embodiments of the invention are better understood with reference to the following drawings.
Different aspects and embodiments are described with reference to the drawings, wherein like reference numerals are generally utilized to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more aspects of embodiments of the invention. It may be evident, however, to one skilled in the art that one or more aspects of the embodiments of the invention may be practiced with a lesser degree of the specific details. In other instances, known structures and devices are shown in block diagram form in order to facilitate describing one or more aspects of the embodiments of the invention. The following description is therefore not to be taken in a limiting sense, and the scope of the invention is defined by the appended claims.
Referring to
The output voltage regulation circuit 22 fulfills its function to generate and maintain a precise and constant output voltage Vout as long as the drop-out voltage, in particular the difference between the input voltage Vin and the output voltage Vout, is above a predetermined level. If, for reasons like degradation of the input power of a battery, the input voltage Vin decreases, then as a result also the drop-out voltage decreases. When the drop-out voltage decreases below the above-mentioned predetermined drop-out voltage level, the voltage regulator 20 can no longer hold the output voltage Vout stable and constant.
Therefore, the output voltage regulation circuit 22 is coupled to a drop-out voltage violation correction circuit 23 the purpose and function of which is to detect the occurrence of a drop-out voltage violation and to cause the output regulation circuit 22 to change the level of the output voltage Vout upon detection of a drop-out voltage violation. A drop-out voltage violation is essentially the decrease of the drop-out voltage below the above-mentioned predetermined level. Therefore, the function of the drop-out violation correction circuit aims to correct the drop-out voltage violation and to bring the drop-out voltage back into an allowable range, namely above the predetermined level. In particular, this is accomplished by causing the output regulation circuit 22 to reduce the level of the output voltage Vout for an amount so as to bring back the drop-out voltage into the allowable range, namely above the predetermined level.
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With the embodiments of voltage regulators of
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With the embodiment of a voltage regulator according to
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The output voltage regulation circuit 52 comprises an input which is coupled to the input port 1 to supply the input voltage Vin to the output voltage regulation circuit 52. The input voltage Vin is then provided to an output stage 52.1 the function of which is to control the current flow between the input and the output of the output voltage regulation circuit 52. The output stage 52.1 may be implemented as a metal oxide semiconductor field-effect transistor (MOSFET), in particular a self-blocking MOSFET, as shown in
The output voltage regulation circuit 52 is coupled to a drop-out voltage violation correction circuit 53. The drop-out voltage violation correction circuit 53 comprises a second resistor R3 comprising a variable and programmable resistance value. The second resistor R3 is coupled with one of its terminals with the second node 52.3 of the output voltage regulation circuit 52. The other terminal of the second resistor R3 is coupled to one of the terminals of a third resistor R2. The other terminal of the third resistor R2 is coupled to ground. The first resistor R1, the second node 52.3, the electric line coupled to the second node 52.3 and the second resistor R3 form together a potential divider. Moreover, the potential divider has variable properties as one of its constituents, namely the second resistor R3 has a variable and programmable resistance value. In particular, if the resistance value of the second resistor R3 is increased, then also the potential at the second node 52.3 is increased so that the feedback voltage Vfb which is tapped off at the second node 52.3 and supplied to the positive input of the operational amplifier 52.4 is also increased. An increase of the feedback voltage Vfb is considered by the output voltage regulation circuit 52 as a respective increase of the output voltage Vout which is in fact not the case as the output voltage Vout has remained constant. As a result, the output voltage regulation 52 reacts so as to decrease the output voltage Vout in order to have the same feedback voltage Vfb as before. Hence, an increase of the resistance value of the second resistor R3 leads to a decrease of the output voltage Vout and thus to an increase of the drop-out voltage. The second resistor R3 may comprise a network of resistors which may be programmed with a digital bit word from the control unit 53.6 to obtain a desired resistance value.
The drop-out voltage violation correction circuit 53 comprises two inputs one of which is for supplying the input voltage Vin and the other one is for supplying the output voltage Vout. The voltage values Vin and Vout are supplied to a comparator circuit comprising a comparator 53.1 and four resistors 53.2, 53.3, 53.4, and 53.5. A fourth resistor 53.2 comprising a resistance value R+r and a fifth resistor 53.3 comprising a resistance value R are connected in series wherein the fourth resistor 53.2 receives the input voltage Vin and the fifth resistor 53.3 is connected with one of its terminals to the fourth resistor 53.2 and with its other terminal to ground. Between the fourth resistor 53.2 and the fifth resistor 53.3 there is provided a node which is connected to the negative input of the comparator 53.1. A sixth resistor 53.4 comprising a resistance value R and a seventh resistor comprising a resistance value R are connected in series wherein the sixth resistor 53.4 receives the output voltage Vout and the seventh resistor 53.5 is connected with one of its terminals to the sixth resistor 53.4 and with its other terminal to ground. Between the sixth resistor 53.4 and the seventh resistor 53.5 there is provided a node which is connected to the positive input of the comparator 53.1. The comparator 53.1 thus compares a voltage which is representative of the input voltage Vin with another voltage which is representative of the output voltage Vout.
If the comparator 53.1 detects that the difference between the voltages input to its positive and negative inputs is below a certain predetermined threshold, it outputs a signal “too_low”. This signal “too_low” is transmitted to a control unit 53.6. The control unit 53.6 then generates and outputs a trim signal to the second variable resistor R3.
The voltage regulator thus allows a lower minimum input voltage Vin for a given voltage regulator drop-out voltage. The comparator 53.1 compares the input voltage Vin and the output voltage Vout (or voltages representative to the input and output voltages) and indicates with the signal “too_low” to the control unit 53.6 if the condition is detected that the input voltage Vin is too low so that the drop-out voltage would be violated. If this condition is detected, the second variable resistor R3 is programmed by the control unit 53.6 to set the output voltage to a lower value as described above. Typically, this procedure would only be enabled at specific instances and be semi-static so as to avoid any dynamic instability in the calibration mechanism.
In the embodiment of
This procedure does guarantee that, as long as the input voltage Vin is within its specified range, inaccuracies in the reference voltage Vref do not cause the drop-out voltage to be exceeded. In the event that Vref is instead too low, the signal “too_low” and the reduction of the output voltage will never be activated, thereby not effecting the accuracy at the lower limit of the output voltage.
In order to deal with variations of the reference and input voltages with time, it is desirable to periodically detect if the trimming can be reduced. This can be done by occasionally attempting to back-off the trimming until the signal “too_low” is indicated, and/or by including a separate comparator that detects when the input voltage is much higher than the output voltage.
Referring to
