Motore di ricerca datesheet componenti elettronici |
|
ML4426IS Scheda tecnica(PDF) 7 Page - Micro Linear Corporation |
|
ML4426IS Scheda tecnica(HTML) 7 Page - Micro Linear Corporation |
7 / 16 page 7 ML4426 CURRENT LIMITING IN THE POWER STAGE The current sense resistor (RSENSE) shown in Figure 1 regulates the maximum current in the power stage and the BLDC motor. Current regulation is accomplished by shutting off the output drivers LA, LB, and LC for a fixed amount of time if the voltage across RSENSE exceeds the current limit threshold. RSENSE The function of RSENSE is to provide a voltage proportional to the motor current to set the current limit trip point. The default trip voltage across RSENSE is 460mV, set by the internal ILIMIT divider ratio. The current sense resistor should be a low inductance resistor such as a carbon composition. For resistors in the milliohms range, wire-wound resistors tend to have low values of inductance. RSENSE should be sized to handle the power dissipation (IMAX2 ´ RSENSE). ISENSE Filter The ISENSE RC lowpass filter is placed in series with the current sense signal as shown in Figure 2. The purpose of this filter is to remove the diode reverse recovery shootthrough current. This current causes a voltage spike on the leading edge of the current sense signal which may falsely trigger the current limit. The current sense voltage waveform is shown before and after filtering in Figure 3. The recommended starting values for this circuit are R = 1k W and C = 330pF. This gives a time constant of 330ns, and will filter out spikes of shorter duration. C can be increased to as much as 2.2nF, but should not exceed a time constant of more than a few microseconds. CIOS When ISENSE exceeds 0.2 ´ ILIMIT, the current limit one- shot is activated, turning off LA, LB, and LC for a fixed amount of time (tOFF). tOFF is set by the amount of capacitance connected to CIOS. CIOS is usually set for a fixed off time equal to or less than the PWM period. For a 25kHz PWM frequency, the PWM period is 40µs; tOFF should be between 20µs and 40µs. The lower limit of tOFF is dictated by the minimum on time of the power stage; a safe approximation is 5µs or less. The equation for finding the CIOS capacitance value is as follows: C tA V OS OFF = 50 24 m . (1) COMMUTATION CONTROL A 3-phase BLDC motor requires electronic commutation to achieve rotational motion. Electronic commutation requires the switching on and off of the power switches of a 3-phase half bridge. For torque production to be achieved in one direction, the commutation is dictated by the rotor position. Electronic commutation in the ML4426 is achieved by turning on and off, in the proper sequence, FUNCTIONAL DESCRIPTION (Continued) Figure 2. Current Sense Circuitry × 5 ISENSE FROM RSENSE PWM ON/OFF – + VREF CIOS 16k Ω 2.9V 0V STOP 30µA START 8k Ω S R Q Q Figure 3. Current Sense Resistor Waveforms (a) Without Filtering, and (b) With Filtering (a) 0V 460mV (b) one N output from one phase and one P output from another phase. There are six combinations of N and P outputs (six switching states) that constitute a full commutation cycle. These combinations are illustrated in Table 1 and Figure 4, and are labeled states A through F. This sequence is programmed into the commutation state machine. Clocking of the commutation state machine is provided by a voltage controlled oscillator (VCO). Forward/Reverse Control The commutation sequence is reversed by pulling the F/R pin to GND. This allows the motor to operate in the opposite direction. This pin should change state only when the motor is at rest. Either remove and restore power to the ML4426, or pull the BRAKE pin and CAT pin to 0V to stop the motor prior to changing the voltage on F/R. Either method resets the internal commutation state machine, and initiates a new start-up sequence. |
Codice articolo simile - ML4426IS |
|
Descrizione simile - ML4426IS |
|
|
Link URL |
Privacy Policy |
ALLDATASHEETIT.COM |
Lei ha avuto il aiuto da alldatasheet? [ DONATE ] |
Di alldatasheet | Richest di pubblicita | contatti | Privacy Policy | scambio Link | Ricerca produttore All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |