Trim circuit for power supply controller

A trim circuit for a power supply controller includes: a control circuit; at least a capacitance type programmable circuit connection; and a switching circuit, under control of the control circuit, the switching circuit selectively coupling the capacitance type programmable circuit connection to anyone of an operation voltage and a programming voltage, for determining a programming state of the capacitance type programmable circuit connection.

BACKGROUND OF THE DISCLOSURE

1. Technical Field

The disclosure relates in general to a trim circuit for a power supply controller and more particularly to a trim circuit having a capacitance type programmable circuit connection.

Electronic devices use power to operate. During conversion, a low frequency (e.g. 50 Hz or 60 Hz) programming voltage alternating current (AC) is converted to programming voltage direct current (DC); the programming voltage DC is converted to high frequency (e.g. 30 to 300 kHz) AC; this high frequency programming voltage AC is transformed (by for example a transformer) to a lower voltage to provide safety isolation. The output of the transformer is rectified to provide a regulated DC output, which may be used to power an electronic device.

In order to compensate process variations, analog integrated circuits such as power supply controllers in the power supply may be commonly trimmed for critical parameters. Trim may be used for wafer sorting (i.e. wafer leveling) or at IC level.

During wafer sorting, the power supply controller may be trimmed using trim pads on the wafer before being assembled in plastic packages. Trimming is done at the wafer level because the trim pads are not usually accessible after assembly. Besides, the assembled parts may be tested again at final test (FT) to eliminate parts shifted too much or damaged during assembly.

Programmable fuses and antifuses allow IC designers to “personalize,” or custom configure, various circuits. A programmable fuse is in a close circuit connection if unprogrammed and in an open circuit connection if programmed. On the contrary, a programmable antifuse is in an open circuit connection if unprogrammed and in a close circuit connection if programmed. Generally, a programmable fuse comprises a fusible conductive link that is broken during programming so that the conductive link no longer closes the circuit. Programmable fuses are a laser programmable type or an electronically programmable type. In both types, the fusible conductive link is broken by heating the link sufficiently so as to melt the link. In the laser programmable type of fuse, a laser provides energy to melt the conductive link. In the electronically programmable type, a relatively large current is passed through the conductive link such that the resistive heating of the link causes the link to melt.

FIG. 1Ashows a prior trim circuit. As shown inFIG. 1A, the sensing circuit110senses the voltage at node N1to output a logic signal SL. The voltage of the node N1is corresponding to the state of the fuse120. In initial fabricated state (i.e. normal state), the fuse120provides a low resistance connection or short circuit connection, so that the logic signal from the sensing circuit110is logic “0”. After the fuse120is programmed, the fuse120provides a high resistance or open circuit connection, so the logic signal from the sensing circuit110turns to logic “1”.

However, in prior art, in order to program the fuse120which may be metal or poly, a large current is required.FIG. 1Bshows the current-voltage (I-V) curve for the prior fuse120. As shown inFIG. 1B, in order to program the metal or poly fuse120, the current must be large enough, for example 400˜800 mA. This large current is provided by an external and large-size current source.

Further, in the prior trim circuit inFIG. 1A, in order to program/trim, each trim bit needs two trim pads130A and130B. The trim pad is large size, for example, 50 μm×50 μm. Further, an external large-size current source is also required to provide a large program current. Therefore, in the prior art, the trim circuit is large sized due to the large-size pads and the external large-size current source.

BRIEF SUMMARY OF THE DISCLOSURE

One example of the disclosure is directed to a trim circuit for a power supply controller, wherein in order to program a programmable circuit connection, a high programming voltage is enough. Thus, neither high external current nor external large-size current source is required. Further, no pad is required. Thus, the circuit size of the trim circuit is small.

According to a exemplary example of the present disclosure, a trim circuit for a power supply controller, includes: a control circuit; at least a capacitance type programmable circuit connection; and a switching circuit, under control of the control circuit, the switching circuit selectively coupling the capacitance type programmable circuit connection to anyone of an operation voltage and a programming voltage, for determining a programming state of the capacitance type programmable circuit connection.

DETAILED DESCRIPTION OF THE DISCLOSURE

First Embodiment

A programmable antifuse is in an open circuit connection if unprogrammed and is in a close circuit connection if programmed. Usually, an antifuse has two conductive regions separated by an insulating region that electrically insulates the two conductive regions from one another. In its unprogrammed state of the antifuse, no current is allowed to pass from one conductive region to the other; and in other words, in its unprogrammed state of the antifuse, the antifuse is in the open circuit connection. When programmed, the insulating region is partially destroyed, allowing current to flow between the two conductive regions; and in other words, in its programmed state of the antifuse, the antifuse is in the short circuit connection. Programming an antifuse results conductive filament that extends within the insulating region between the two conductive regions.

In the embodiments of the disclosure, the antifuse is electronically programmable, i.e., programmable by charging with a high voltage to cause the insulating region to become at least partially conductive. One type of programmable antifuse disclosed by the embodiment of the disclosure is a capacitance antifuse.

FIG. 2Ashows a trim circuit according to a first embodiment of the disclosure. The trim circuit according to the first embodiment includes a control circuit210, a current source220, a programmable circuit connection and switches SW11˜12. In the embodiment, the programmable circuit connection230is, for example but not limited to, a capacitance type antifuse230. O/P refers to an output terminal.

According to the trim bit TB, the control circuit210controls the conduction states of the switches SW11˜12by the control signals SC1and SC2and therefore determines the program state of the antifuse230.

The current source220provides a constant current to the antifuse230. The current source220is small size. The current-voltage (I-V) curve of the antifuse230is shown inFIG. 2B. As shown inFIG. 2B, in the first embodiment, the antifuse230is in open circuit connection (in permanent high resistance connection) when the voltage applied thereto is lower than a threshold value (for example but not limited to 20V). The antifuse230is programmed into the short circuit connection (in low resistance connection) when the voltage applied thereto is higher than the threshold value.FIG. 2Cshows a possible layout structure of the capacitance type antifuse230. Since it is a traditional layout of a capacitance, so the description is omitted here.

The switch SW11is selectively coupled between the programming voltage HV and the antifuse230; and the conduction state thereof is controlled by the control signal SC1from the control circuit210. The switch SW12is selectively coupled between the current source220and the antifuse230(i.e. the switch SW12being coupled between the operation voltage VDD and the antifuse230); and the conduction state thereof is controlled by the control signal SC2from the control circuit210. The conduction states of the switches SW11˜12is opposite. In other words, when the switch SW11is conducted, the switch SW12is turned off and in an open state; and vice versa.

When the trim bit TB representing the antifuse230is unprogrammed (i.e. in open circuit connection), the control circuit210controls the switch SW12in a conducted state (i.e. a turned on state) and the switch SW11in a non-conducted state (i.e. a turned off state). The operation voltage VDD (for example but not limited to, 5V) is applied to the antifuse230via the conducted switch SW12but the programming voltage HV (for example but not limited, higher than 20V) is not applied to the antifuse230because of the non-conducted switch SW11. Because the antifuse230is applied by 5V lower than the threshold value, the antifuse230is unprogrammed.

When the trim bit TB representing the antifuse230is to be programmed (i.e. in short circuit connection), the control circuit210controls the switch SW12in the non-conducted state and the switch SW11in the conducted state. The operation voltage VDD is not applied to the antifuse230but the programming voltage HV is applied to the antifuse230via the conducted switch SW11. Because the antifuse230is applied by the programming voltage HV (>25V) higher than the threshold value, the antifuse230is programmed. Further, after the antifuse230is programmed, the antifuse230becomes permanently shorted and no longer provides a high resistance connection.

AlthoughFIG. 2Ashows only one antifuse230, the first embodiment is not limited. The trim circuit may include a plurality of parallel antifuses230and the program state of each antifuse is independently controlled by the control circuit210.

Further, each critical parameter for the power supply controller may be trimmed to the desired accuracy by allocating a number of programmable circuit connections to that parameter. When more than one programmable circuit connection is assigned to the same critical parameter, each programmable circuit connection trim is designed to have different weight affecting the critical parameter. Thus, if a parameter is off from the designed value, a proper combination of the programmable circuit connections assigned to the parameter can be programmed for overcoming this problem.

Second Embodiment

FIG. 3shows a trim circuit according to a second embodiment of the disclosure. The trim circuit according to the second embodiment includes a control circuit310, a current source320, a programmable circuit connection330, a logic circuit340and switches SW31˜33. The programmable circuit connection330in the second embodiment is for example but not limited to a capacitance type antifuse.

The control circuit310controls the conduction states of the switches SW31˜33and therefore the state of the antifuse330is corresponding to the trim bit TB.

The current source320provides a constant current to the antifuse330. The current source320is also small size.

The control circuit310controls the conduction states of the switches SW31˜SW33to determine whether the antifuse330is programmed or unprogrammed. In the second embodiment, for example but not limited, the conduction state of the switches SW31˜SW32is opposite to the conduction state of the switch SW33.

The logic circuit340in the second embodiment is for example but not limited by an inverter. The logic circuit340inverts the control signal SCfrom the control circuit310and provides the inverted control signal to the switch SW33. The control signal SCis also provided to the switch SW31. In other words, the switches SW32and SW33have opposite conduction states.

The switch SW31is selectively coupled between the output 0/P and ground. If the antifuse330is to be programmed, the switch SW31is non-conducted and vice versa. The switch SW32is selectively coupled between the operation voltage VDD and the current source320. In other words, the switch SW32is coupled between the operation voltage VDD and the antifuse330. If the antifuse330is to be programmed, the switch SW32is non-conducted and vice versa. The switch SW33is selectively coupled between the programming voltage HV and the current source320. In other words, the switch SW33is coupled between the programming voltage HV and the antifuse330. If the antifuse330is to be programmed, the switch SW33is conducted and vice versa.

When the trim bit TB representing the antifuse330is unprogrammed (i.e. in open circuit connection), the control circuit310controls the switches SW31and SW32in the conducted state and controls the switch SW33in the non-conducted state. Accordingly, the operation voltage VDD is coupled the antifuse330due to the conducted switches SW32and SW31, but the programming voltage HV is not applied to the antifuse330because of the non-conducted switch SW33. Because the antifuse330is applied by the operation voltage lower than the threshold value, the antifuse330is unprogrammed.

When the trim bit TB indicates that the antifuse330is to be programmed (i.e. in short circuit connection), the control circuit310controls the switches SW31and SW32in the non-conducted state and controls the switch SW33in the conducted state. Accordingly, the operation voltage VDD is not applied to the antifuse330but the programming voltage HV is applied to the antifuse330via the conducted switch SW33. Because the antifuse330is applied by the programming voltage HV (>25V) higher than the threshold value, the antifuse330is programmed.

AlthoughFIG. 3shows only one antifuse330, the second embodiment is not limited. The trim circuit may include a plurality of parallel antifuses330and the program state of each antifuse is independently controlled by the control circuit310.

In the above embodiments of the disclosure, in order to program the capacitance type programmable circuit connection, a high voltage is enough and thus neither high external current nor large external current source is required. Further, in order to program the capacitance type programmable circuit connection, no pad is required. Thus the circuit size of the trim circuit according to the above embodiments of the disclosure is small.

It will be appreciated by those skilled in the art that changes could be made to the disclosed embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that the disclosed embodiments are not limited to the particular examples disclosed, but is intended to cover modifications within the spirit and scope of the disclosed embodiments as defined by the claims that follow.