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UC3625J 데이터시트(PDF) 5 Page - Texas Instruments |
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UC3625J 데이터시트(HTML) 5 Page - Texas Instruments |
5 / 15 page 5 UC1625 UC2625 UC3625 Dir, Speed-In: The position decoder logic translates the Hall signals and the Dir signal to the correct driver sig- nals (PUs and PDs). To prevent output stage damage, the signal on Dir is first loaded into a direction latch, then shifted through a two-bit register. As long as Speed-In is less than 250mV, the direction latch is transparent. When Speed-In is higher than 250mV, the direction latch inhibits all changes in direc- tion. Speed-In can be connected to Tach-Out through a filter, so that the direction latch is only transparent when the motor is spinning slowly, and has too little stored en- ergy to damage power devices. Additional circuitry detects when the input and output of the direction latch are different, or when the input and output of the shift register are different, and inhibits all output drives during that time. This can be used to allow the motor to coast to a safe speed before reversing. The shift register guarantees that direction can't be changed instantaneously. The register is clocked by the PWM oscillator, so the delay between direction changes is always going to be between one and two oscillator pe- riods. At 40kHz, this corresponds to a delay of between 25 µs and 50µs. Regardless of output stage, 25µs dead time should be adequate to guarantee no overlap cross-conduction. Toggling DIR will cause an output pulse on Tach-Out regardless of motor speed. E/A In(+), E/A In(–), E/A Out, PWM In: E/A In(+) and E/A In(–) are not internally committed to allow for a wide variety of uses. They can be connected to the ISENSE,to Tach-Out through a filter, to an external command volt- age, to a D/A converter for computer control, or to an- other op amp for more elegant feedback loops. The error amplifier is compensated for unity gain stability, so E/A Out can be tied to E/A In(–) for feedback and major loop compensation. E/A Out and PWM In drive the PWM comparator. For voltage-mode PWM systems, PWM In can be connected to RC-Osc. The PWM comparator clears the PWM latch, commanding the outputs to chop. The error amplifier can be biased off by connecting E/A In(–) to a higher voltage than E/A In(+). When biased off, E/A Out will appear to the application as a resistor to ground. E/A Out can then be driven by an external am- plifier. GND: All thresholds and outputs are referred to the GND pin except for the PD and PU outputs. H1, H2, H3: The three shaft-position sensor inputs con- sist of hysteresis comparators with input pull-up resis- tors. Logic thresholds meet TTL specifications and can be driven by 5V CMOS, 12V CMOS, NMOS, or open-collectors. Connect these inputs to motor shaft position sensors that are positioned 120 electrical degrees apart. If noisy signals are expected, zener clamp and filter these inputs with 6V zeners and an RC filter. Suggested filtering components are 1k Ω and 2nF. Edge skew in the filter is not a problem, because sensors normally generate modified Gray code with only one output changing at a time, but rise and fall times must be shorter than 20 µs for correct tachometer operation. Motors with 60 electrical degree position sensor coding can be used if one or two of the position sensor signals is inverted. ISENSE1,ISENSE2,ISENSE: The current sense amplifier has a fixed gain of approximately two. It also has a built-in level shift of approximately 2.5V. The signal ap- pearing on ISENSE is: () () I V ABS I I SENSE SENSE SENSE =+ • 25 2 12 .– ISENSE1 and ISENSE2 are interchangeable and can be used as differential inputs. The differential signal applied can be as high as ±0.5V before saturation. If spikes are expected on ISENSE1 or ISENSE2, they are best filtered by a capacitor from ISENSE to ground. Fil- tering this way allows fast signal inversions to be cor- rectly processed by the absolute value circuit. The peak-current comparator allows the PWM to enter a cur- rent-limit mode with current in the windings never ex- ceeding approximately 0.2V/RSENSE. The over current comparator provides a fail-safe shutdown in the unlikely case of current exceeding 0.3V/RSENSE. Then, soft start is commanded, and all outputs are turned off until the high current condition is removed. It is often essential to use some filter driving ISENSE1 and ISENSE2 to reject ex- treme spikes and to control slew rate. Reasonable start- ing values for filter components might be 250 Ω series resistors and a 5nF capacitor between ISENSE1 and ISENSE2. Input resistors should be kept small and matched to maintain gain accuracy. OV-Coast: This input can be used as an over-voltage shutdown in put, as a coast input, or both. This input can be driven by TTL, 5V CMOS, or 12V CMOS. PIN DESCRIPTIONS |
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