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ML4423 bảng dữ liệu(PDF) 6 Page - Micro Linear Corporation |
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ML4423 bảng dữ liệu(HTML) 6 Page - Micro Linear Corporation |
6 / 10 page ML4423 6 Current Limit Motor current is sensed on ISENSE (pin 16). RLIMIT should be selected so that R V I LIMIT MAX = 05 . (4) For a 2A current limit, RLIMIT = 0.25W. The 1kW resistor and 330pF capacitor filter (shown in figure 3) filter the high frequency flyback pulses (due to the freewheeling diode recovery currents) occurring at the output. When IMAX is reached the output power will be turned off for the remainder of the current PWM cycle, which is asynchronous with the sinewave frequency. Thus current limit is fixed-period with variable duty cycle. PWM SINE Controller This circuit block compares the sinewaves at SINEA and SINEB to the sampled inputs SENSEA–SENSEC and SENSEB–SENSEC, respectively. The PWM loop then drives the outputs to force these “differential” waveforms to equal the internal reference waveforms at SINEA and SINEB. The differential signals SENSEA–SENSEC and SENSEB–SENSEC will be approximately 1.7 volts zero- peak maximum. The signals at these pins should be filtered to remove the PWM frequency. The high voltages at the motor terminals are divided down to 1.7V to provide voltage feedback to the controller. In figure 3, the resistors to ground from SENSEA (pin 1) and SENSEB (pin 3) should be 1k W. SENSEC (pin 2) should have a 500 W to ground because it has 1/2 the input impedance of the other 2 inputs. The 0.15 mF capacitors to ground on SENSEA and SENSEB and the 0.3mF capacitor to ground on SENSEC will create a 1kHz low pass filter at these inputs. VPEAK on the motor is set by the divider ratios. For the values shown in figure 3: (VSPEED = 4.4V) VV kk k V k V PEAK = + = + = 17 99 1 1 17 49 5 500 500 170 . . . (5) OUTPUT DRIVE The 6 output drivers of the ML4423 drive the H and L outputs from 0 to 12 volts (with pin 25 tied to VCC+(12V)). The outputs will drive about 10mA and are designed to drive output buffers and high side drivers requiring 12V swings. The ML4423 provides lower current 0 to 5V drive for high/low side drivers requiring 5V input signal swings with pin 25 left unconnected. PROGRAMMABLE DEADTIME A dead time circuit is provided to prevent shoot through currents in the power output stage. The dead time is controlled by a resistor to ground on RDT (pin 9). The dead time selected should be large enough to prevent cross conduction between the upper and lower power devices of each inverter phase leg. tR DEAD DB =× () − 12 10 11 . (6) With fPWM = 25kHz, the PWM period is 40ms. With RDB = 166k, tDEAD = 2ms (~5%). CGM1 and CGM2 These two external capacitors to ground each set a pole in the forward path of the feedback loop in conjunction with a gm of 1/650W. The pole should be placed at a frequency higher than the PWM frequency. g C f m gm PWM 2 π > (7) APPLICATION The ML4423 provides all the signals necessary to drive the output power stage connected to the motor. The components around the ML4423 for a typical application are shown in figure 3. The motor DC supply voltage should be greater than the largest signal waveform required or output clipping may result. Figure 4 shows an alternate circuit using the IR2118. |
Số phần tương tự - ML4423 |
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Mô tả tương tự - ML4423 |
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