JAJSOR1D june 2022 – august 2023 LM5177
PRODUCTION DATA
The integrated peak current sensor enables a low inductive sensing as it is located in series with the main inductor. It also can monitor the peak inductor current under all operation modes (boost, buck-boost and buck ) as well as for both current directions i.e. the bi-directional operation.
As the integrated sensor supports high bandwidth signals a differential mode filter adopted to the selected switching frequency is recommended for best performance. For most applications we recommend a resistor value for R(DIFF1/2) of 100 Ω. You can use the equation below to determine the filter capacitor:
Where the lowest corner frequency for the differential filter should be five times the selected switching frequency.
For input voltages above 40V it is recommended to place additional filter capacitors between the filter resistor to GND. For most tested applications and PCB's a value of 47 pF for C(COMM1/2) and achieved sufficient suppression of the common mode switching noise for the current sensor. The above boundaries are determined with suitable applicative PCB and multiple device units during a start-up into the current limit.
Current sense resistors consist a parasitic inductance based on their geometry and the selected component vendors design. If the desired application requires high currents the impact of the external component parasitic can be reduced by placing multiple sense resistors in parallel.
The low and accurate peak current sense threshold of 50 mV (typ.) enables a power stage design with small losses over the external sense resistor and a small deviation of the inductor saturation current relative to the average inductor current. Although if there is noise coupling on the PCB or injected to the device a reaction of an increase output ripple caused by a neg. current spike in the inductor are observed. If this behavior (see Figure 8-17 ) is not suppressed by
The negative inductor current build up can be predicted by a maximum of 3 switching cycles with the following equation: