Chip with in-circuit programability

1. A circuit for enabling an IC to have a normal mode for performing normal functions and a program mode for programming settings of the IC, the circuit comprising:

a demultiplexer circuit for providing the input data as normal data when the IC is in the normal mode and as program data when the IC is in the program mode; and

a program enable circuit for providing a program enable signal to switch the IC to the program mode.

2. The circuit of claim 1 , further comprising

an input circuit for receiving the input data;

internal circuits for processing the input data as normal data; and

a program circuit for processing the input data as program data,

wherein, when the program enable signal is OFF the demultiplexer circuit provides the normal data to internal circuits and when the program enable signal is ON the demultiplexer circuit provides the program data to the program circuit.

3. The circuit of claim 1 , wherein the program enable circuit is connected to first and second pins of the IC and provides the program enable signal when a voltage difference between the first and second pins reaches a preset value, the program enable signal indicating the IC switching from the normal to the program mode.

4. The circuit of claim 3 , wherein the program enable circuit further comprises at least one operational amplifier, each operational amplifier controlling a switch.

5. The circuit of claim 3 , wherein when the IC is in the program mode the program circuit sets signal bits addressed by the program data.

6. The IC of claim 5 , wherein the program circuit comprises a plurality of zap circuits each having a fusible diode and a transistor switch.

7. The IC of claim 6 , wherein each zap circuit is controlled by an enabling circuit that allows the zap circuit to blow the fusible diode when data is received from the demultiplexer circuit.

8. The IC of claim 1 , wherein the IC is an Intelligent Power Switch.

9. The IC of claim 2 , wherein the input circuit is a level shift circuit.

10. A circuit for enabling an IC having a normal mode for performing normal functions and a program mode for programming settings of the IC to use same pins in both modes, the circuit comprising:

an input circuit for receiving the input data;

internal circuits for processing the input data in the normal mode;

a program circuit for processing the input data in the program mode,

a program enable circuit for providing a program enable signal for switching the IC from the normal to the program mode; and

a demultiplexer circuit for providing the input data as normal data to internal circuits when the IC is in the normal mode and as program data to the program circuit when the IC is in the program mode.

11. The circuit of claim 10 , wherein the program enable circuit is connected to first and second pins of the IC and provides the program enable signal when a voltage difference between the first and second pins reaches a preset value.

12. The circuit of claim 11 , wherein, when the program enable signal is OFF the IC operates in the normal mode and when the program enable signal is ON the IC switches from the normal to the program mode.

13. A circuit for enabling programming of settings in an IC from pins of the IC, the circuit comprising:

an input circuit receiving input data from an external pin of the IC;

a demultiplexer circuit coupled to the input circuit for receiving the input data and forwarding the input data to internal circuits for normal mode IC operation and forwarding the input data to a program circuit for program mode IC operation;

a program enable circuit for providing a program enable signal for switching the IC between a normal mode and a program mode; and

wherein in the program mode the program circuit sets bits addressed by the input data provided by the demultiplexer.

14. The circuit of claim 13 , wherein the program enable circuit provides a program enable signal when a voltage difference between two predetermined pins of the IC reaches a preset value.