DC-DC converters having improved current sensing and related methods

Abstract

A DC-DC converter includes a chip including an error amplifier and a pulse width modulator (PWM) having an input connected to an output of the error amplifier, and an inductor driven by said PWM in series with an output node (VOUT) of the converter, wherein a load current flows through the inductor. VOUT is fed back through a network including a feedback resistor (RFB) to an inverting input of the error amplifier. A circuit for sensing the load current includes a first operational amplifier, a sense resistor on the chip having resistance RSENSE coupled to an inverting input of the first amplifier; wherein a sense current related to the load current flows through the sense resistor, a dependent current source provides an output current to supply the sense current. A reference resistor is disposed on the chip having a resistance RREFERENCE which is a fixed multiple of RSENSE. A set resistor is provided having a resistance RSET. Tracking circuitry sets a voltage across the reference resistor to be equal to a voltage across the set resistor. A function block is coupled to receive a current through the set resistor and a current through the reference resistor to find their ratio. A current multiplier is provided, wherein an output of the function block is coupled to the current multiplier. The current multiplier provides a measurement current which is proportional to the load current divided by RSET.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application claims the benefit of Provisional Application No. 60 / 808,197 ENTITLED “METHOD OF IMPROVED CURRENT SENSING IN DC-DC CONVERTERS” filed on May 24, 2006, which is incorporated by reference in its entirety in the present application.FIELD OF THE INVENTION[0002]The invention relates to the precise measurement of inductor current, especially for controlling switching in voltage regulator circuits and related power circuits.BACKGROUND OF THE INVENTION[0003]It is necessary to accurately measure load current in order to accomplish control of a variety of devices including electric current motors, DC-DC converter circuits and voltage regulator circuits. A known circuit 100 for measuring load current via inductor current flow in a DC-DC converter is shown in FIG. 1(a). The portion of circuit 100 to the right of the vertical dashed line between pins ISENSE− and ISENSE+ is typically internal to the IC chip, while the portion including ...

AI Technical Summary

Benefits of technology

[0011]A DC-DC converter includes a chip including an error amplifier and a pulse width modulator (PWM) having an input connected to an output of the error amplifier, and an inductor driven by said PWM in series with an output node (VOUT) of the converter, wherein a load current flows through the inductor. VOUT is fed back through a network including a feedback resistor (RFB) to an inverting input of the error amplifier. A circuit for sensing the load current includes a first operational amplifier, a sense resistor on the chip having resistance RSENSE coupled to an inverting input of the first amplifier; wherein a sense current related to the load current flows through the sense resistor, a dependent cur

Problems solved by technology

A second reason that RSENSE is usually placed external to the IC is that most integrated circuit processes do not support an accurate and stable, internal resistor.

A problem with an external RSENSE is the susceptibility of the ISENSE+ pin to noise pickup indicated in FIG. 1(a) and 1(b) as noise coupling through parasitic capacitor 130.

Such noise coupling is known to adversely impact performance and has required very careful printed circuit board layouts to minimize the capacitive coupling at pin ISENSE+.

It is not generally feasible to try to bypass ISENSE+, as this would put a pole in the feedback of amplifier A1, possibly making A1 unstable.

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