High-Side Current Estimation in Buck Converters Without Shunt Loss
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Solution Overview
Problem
Existing current sensing methods for inductive loads in power converters, such as buck converters, are inefficient and inaccurate, particularly for high-side current measurements, leading to power dissipation and reliability issues, especially at short duty cycles.
Innovation Solution
A current sensing circuit that estimates high-side current based on low-side current measurements during the low-side switch conduction time, using a current amplifier, output voltage estimator, and inductance estimator to calculate the high-side current without requiring shunt resistors, and includes auto-calibration for accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If shunt resistors are used for high-side current measurements, then current measurement capability is improved, but power dissipation increases and reliability decreases
Solution Approach 1:
The patent measures low-side current through the low-side switch and uses this measurement to calculate and estimate the high-side current, rather than directly measuring high-side current with shunt resistors. This copying approach eliminates the need for high-side shunt resistors, reducing power dissipation while maintaining measurement capability through mathematical relationship: I_high_side = I_low_side + C*dV/dt
Solution Approach 2:
The patent replaces the physical shunt resistor measurement method with an electrical calculation method using voltage measurements across the low-side switch and capacitor current relationships. This substitution eliminates the need for power-dissipating shunt resistors in the high-side current path while providing accurate current estimation through electrical parameter relationships
2Measurement precision
If shunt resistors are used for high-side current measurements, then current measurement capability is improved, but reliability decreases
Solution Approach 1:
The patent measures low-side current through the low-side switch and uses this measurement to calculate and estimate the high-side current, rather than directly measuring high-side current with shunt resistors. This copying approach eliminates the need for high-side shunt resistors, reducing power dissipation while maintaining measurement capability through mathematical relationship: I_high_side = I_low_side + C*dV/dt
Solution Approach 2:
The patent replaces the physical shunt resistor measurement method with an electrical calculation method using voltage measurements across the low-side switch and capacitor current relationships. This substitution eliminates the need for power-dissipating shunt resistors in the high-side current path while providing accurate current estimation through electrical parameter relationships
3Loss of energy
If low-side current sensing is used to estimate high-side current, then power dissipation is reduced, but measurement accuracy worsens at short duty cycles
Solution Approach 1:
The patent incorporates feedback mechanisms including auto-calibration functionality that adjusts measurement parameters based on operating conditions. The system continuously monitors the relationship between low-side and high-side currents and adjusts estimation algorithms to maintain accuracy across varying duty cycles, particularly compensating for short duty cycle conditions where measurement accuracy would otherwise deteriorate
Data Source
Figure 1~2
Figure 3a~3e
Figure 4
AI summary
A high-side switch (Q1) comprises a high-side control terminal configured to receive a high-side control signal (DRV1) as well as a current flow path therethrough between the high-side reference node (VIN) and the switching node (SW), the high-side switch (Q1) being configured to be made conductive in response to the high-side control signal (DRV1) having a first logic value during a first time interval (HSON). A low-side switch (Q2) comprises a low-side control terminal configured to receive a low-side control signal (PWM, DRV2) as well as a current flow path therethrough between the switching node (SW) and the low-side reference node (PGND), the low-side switch (Q2) being configured to be made conductive in response to the low-side control signal (DRV2) having said first logic value during a second time interval (LSON). The method comprises coupling an inductive element (L) to the switching node (SW) and to an output node (Vout) configured to be coupled to a load (30), and providing a sensed switching voltage (VSW) to a filter circuit (42) configured to provide a filtered voltage (Vo_est) based on said sensed switching voltage (VSW), the filtered voltage (Vo_est) indicative of the output voltage at said output node (Vout). Based on a difference (VIND) between said filtered voltage (Vo_est) and said sensed switching voltage (VSW), the method provides (43, 44, 46) to user circuitry (48) an output current signal (IHS_est, ISENSE) indicative of the intensity of a current through the inductive load (L) during an estimation time (ΔTEST) equal to or greater than said first time interval (HSON).