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Integrating the Trimming & Satisfying the Customer’s Needs, Part 1

The switching DC-to-DC converters are a widely used solution for portable consumer applications to generate a voltage output that is either higher than the input voltage (i.e., a boost or step-up configuration) or lower (buck or step down configuration). In addition, the switching supplies exhibit high efficiency of power conversion from input to output.

The basic principle of operation of this kind of circuit is based on the fact that in a cyclic mode of operation, performed by opening and closing one or more electronic switches periodically (i.e., repeating every T seconds; see Figure 1), the current that flows into the inductor is periodic:

IL (0) = IL (T) = IL (2T).

Figure 1

At the top, a DC:DC converter (general schematic of a step down or buck converter and the inductor current); below, the two half cycles of operation shown at the left and right. At the left, the switch is closed and the diode is not conducting. At the right, the switch has opened and the diode conducts.

At the top, a DC:DC converter (general schematic of a step down or buck converter and the inductor current); below, the two half cycles of operation shown at the left and right. At the left, the switch is closed and the diode is not conducting. At the right, the switch has opened and the diode conducts.

Hence, utilizing the typical equation that describes the relationship between the voltage and the current in an inductor:

We see that the integral on a period of the voltage across the inductor is zero:

We can evaluate the integral of the voltage across the inductor for the particular configuration considered (step up, step down, etc.). When we do that, we get the typical voltage conversion ratio for the continuous mode of operation as shown below:

To regulate the output voltage, it’s enough to regulate the duty cycle of the switch. But one has to be sure that the timing for the switch (or switches) is operating in continuous mode (i.e., the inductor current never drops all the way to zero during the switching period; see IL waveform in Figure 1).

I have been in charge of the designing of an integrated voltage switching regulator. Here, all the components of the DC:DC switching converter were integrated into silicon with the exception of the inductor and the bypass and filter capacitors (see Figure 2).

Figure 2

The first version of the step up DC/DC converter with external trimming. One or multiple switches would be closed to set VOUT.

The first version of the step up DC/DC converter with external trimming. One or multiple switches would be closed to set VOUT .

The voltage regulator that I had to qualify had some additional features. There was an Under Voltage Lock Out block (accessible from the UVLO pin) and the Enable Switching block (accessible from the EN pin). These blocks enable (or disable) the switching of the power MOSFETs when the input voltage rises above (or drops below) a threshold; or by a logic control signal. The threshold value can be set by a network of resistors that, in the first release of the product, was external to the integrated device. A logic sequence of bits (closing the proper switches) can be programmed by the customer, setting the resistor value seen from the internal voltage reference (see Figure 2).

This solution was not acceptable to me, because, from my point of view, the customer’s need is to have a finalized solution for the particular application of interest, so I asked to the design team to integrate a trimming network of resistors and to adopt for the switches a fusible solution (see Figure 3).

Figure 3

The updated version of the step up DC:DC converter with integrated trimming protocol. CREF represents the fuse-programmable resistors.

The updated version of the step up DC:DC converter with integrated trimming protocol. CREF represents the fuse-programmable resistors.

The design team performed the task and generated a trimming table containing the correspondence between the logic sequences and the percentage of trimming of the reference voltage:

Table 1

Trimming table

Trimming table

Utilizing the trimming info from Table 1, I programmed the trimming procedure by a special code that I inserted into the testing program at final test stage. This solution was really appreciated by the customer — they had the product exactly as it was requested. Moreover, I had the possibility of modifying the product for other customers, satisfying each request, just by fixing my testing program.

Have you ever experienced an integrating of a functional block that was customer oriented? Do you believe that integration can enhance the effectiveness of an engineer in charge of the start-up of the mass production, making him able to address the customers’ requirements?

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3 comments on “Integrating the Trimming & Satisfying the Customer’s Needs, Part 1

  1. etnapowers
    October 24, 2013

    This story is an example of how the integration of functions inside a chip, can make the product tunable for a specific customer and winning the business.

  2. etnapowers
    October 25, 2013

    This integration strategy led to a space saving giving the chance to the customer to have more block and hence more functionalities onto the application board.

  3. yalanand
    October 27, 2013

    The changing DC-to-DC converters are an extensively used solution for movable consumer applications to create a voltage output that is either higher than the input voltage (for example, a boost or step-up config) or lower (buck or step down config). Furthermore, the switching provisions exhibit high proficiency of power exchange from input to output.

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