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L6206 Arkusz danych(PDF) 9 Page - STMicroelectronics |
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L6206 Arkusz danych(HTML) 9 Page - STMicroelectronics |
9 / 53 page 9/53 AN1762 APPLICATION NOTE Figure 8. Two situations that must be avoided. 3.5 Sensing Resistors Each motor winding current is flowing through the corresponding sensing resistor, causing a voltage drop that can be used, by the logic (integrated in the L6207; an external logic can be used with L6205 and L6206), to control the peak value of the load current. Two issues must be taken into account when choosing the RSENSE value: – The sensing resistor dissipates energy and provides dangerous negative voltages on the SENSE pin during the current recirculation. For this reason the resistance of this component should be kept low. – The voltage drop across RSENSE is compared with a reference voltage (on Vref pin) by the internal com- parator (L6207 only). The lower is the RSENSE value, the higher is the peak current error due to noise on Vref pin and to the input offset of the current sense comparator: too small values of RSENSE must be avoided. A good compromise is calculating the sensing resistor value so that the voltage drop, corresponding to the peak current in the load (Ipeak), is about 0.5 V: RSENSE = 0.5 V / Ipeak. It should be clear that sensing resistor must absolutely be non-inductive type in order to avoid dangerous neg- ative spikes on SENSE pins. Wire-wounded resistors cannot be used here, while Metallic film resistors are rec- ommended for their high peak current capability and low inductance. For the same reason the connections between the SENSE pins, C6, C7, VSA, VSB and GND pins (see Figure 7) must be taken as short as possible (see also the Layout Considerations section). The average power dissipated by the sensing resistor is: Fast Decay Recirculation: PR ≈ Irms 2 · RSENSE Slow Decay Recirculation: PR ≈ Irms 2 · RSENSE · D, D is the duty-cycle of the PWM current control, Irms is the r.m.s. value of the load current. GND GND GND GND SENSEA SENSEB VSA VSB R5 C7 C6 L6205, L6206, L6207 DON’T connect the Logic GND here Voltage drop due to current in sense path can disturb logic GND. DON’T put a diode here! Recirculating current cannot flow into the bulk capacitor and causes a high voltage spike that can destroy the IC. + - VS = 8 ÷ 52 V |
Podobny numer części - L6206 |
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Podobny opis - L6206 |
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