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PBM3960-1 Datasheet(PDF) 6 Page - Ericsson |
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PBM3960-1 Datasheet(HTML) 6 Page - Ericsson |
6 / 10 page PBM 3960/1 6 Where (L 62 … L42) is the level pro- grammed in channel 2’s level register. (D 6 … D0) and (Q62 … Q02) are the new and old values of DA-Data2. The two level registers, LEVEL1 and LEVEL2, consist of three flip flops each and they are compared against the three most significant bits of the DA- Data value, sign bit excluded. DA 1 and DA2 These are the two outputs of DAC1 and DAC2. Input to the DACs are internal data bus (Q 61 … Q01) and (Q62 … Q02). Reference Voltage V Ref V Ref is the analog input for the two DACs. Special care in layout, gives a very low voltage drop from pin to resistor. Any V Ref between 0.0 V and VDD can be applied, but output might be non- linear above 3.0 V. Power-on Reset This function automatically resets all internal flip flops at power-on. This results in V SS voltage at both DAC outputs and all digital outputs. Figure 10. Table showing how data is transfered inside PBM 3960/1. Figure 9. Motor current dragging at high step rates and current decay influence. Fast current decay will make it possible for the current to follow the ideal sine curve. Output shown without sign shift. Figure 8b. An example of accessible positions with a given torque deviation/ fullstep. Note that 1:st µstep sets highest resolution. Data points are exaggerated for illustration purpose. TNom = code 127. Where (D 6 … D0) is the new value being sent to DA-Data1 and (Q 61 … Q01) is DA- Data1’s old value. (L 61 … L41) are the three bits for setting the current decay level at LEVEL1. The logic definition of CD 2 is analog to CD 1: CD 2 = NOT{[(D 6 … D0) < (Q62 … Q02)] AND[(D 6 …D4) < (L62 … L42)]} Reset If Reset is not used, leave it disconnec- ted. Reset can be used to measure leakage currents from V DD. Applications Information How Many Microsteps? The number of true microsteps that can be obtained depends upon many different variables, such as the number of data bits in the Digital-to-Analog converter, errors in the converter, acceptable torque ripple, single- or double-pulse programming, the motor’s electrical, mechanical and magnetic characteristics, etc. Many limits can be found in the motor’s ability to perform properly; overcome friction, repeatability, torque linearity, etc. It is important to realize that the number of current levels, 128 (27), is not the number of steps available. 128 is the number of current levels (reference voltage levels) available from each driver stage. Combining a current level in one winding with any of 128 other current levels in the other winding will make up 128 current levels. So expanding this, it is possible to get 16,384 (128 • 128) combinations of different current levels in the two windings. Remember that these 16,384 micro-positions are not all useful, the torque will vary from 100% to 0% and some of the options will make up the same position. For instance, if the current level in one winding is OFF (0%) you can still vary the current in the other winding in 128 levels. All of these combinations will give you the same position but a varying torque. Typical Application The microstepper solution can be used in a system with or without a micro- processor. Without a microprocessor, a counter addresses a ROM where appropriate step data is stored. Step and Direction are the input signals which represent clock and up / down of counter. This is the ideal solution for a system where there is no microprocessor or it is heavily loaded with other tasks. With a microprocessor, data is stored in ROM / RAM area or each step is successively calculated. PBM 3960/1 is connected like any peripheral addressa- ble device. All parts of stepping can be tailored for specific damping needs etc. T [mNm] 1 T [mNm] 2 max T nom T min T DA output [V] t Current dragging Time CD CS A0 A1 Data Transfer 0 0 0 D7 —> Sign1, (D6—D0) —> (Q61—Q01), New value —> CD1 0 0 1 (D6—D4) —> (L61—L41) 0 1 0 D7 —> Sign2, (D6—D0) —> (Q62—Q02), New value —> CD2 0 1 1 (D6—D4) —> (L62—L42) 1 X X No Transfer I [mA] 1 I [mA] 2 I Figure 8a. Assuming that torque is proportional to the current in resp. winding it is possible to draw figure 8b. |
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