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công cụ tìm kiếm bảng dữ liệu linh kiện điện tử |
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công cụ tìm kiếm bảng dữ liệu linh kiện điện tử |
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MC33690DW bảng dữ liệu(PDF) 6 Page - Freescale Semiconductor, Inc |
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MC33690DW bảng dữ liệu(HTML) 6 Page - Freescale Semiconductor, Inc |
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6 / 24 page  MOTOROLA SEMICONDUCTORS PRODUCTS 6 revision 4.8, 5 February 2002 © Motorola, Inc., 2002. MC33690 Read function When answering to the base station, a transponder generates an absorption modulation of the magnetic field. It results in an amplitude/ phase modulation of the current across the antenna. This information is picked up at the antenna tap point between the coil and the capacitor. An external resistive ladder down scales this voltage to a level compatible with the demodulator input voltage range (see parameter VINRD page 16). The demodulator (see figure 2) consists of : - an input stage (emitter follower), - a sample & hold circuit, - a voltage follower, - a low offset voltage comparator. The sampling time is automatically set to take into account a phase shift due to the tolerances of the antenna components (L and C) and of the oscillator. The allowed phase shift measured at the input RD ranges from -45° to +45°. Assuming that the phase reference is the falling edge of the driving signal TD1, this leads to a sampling time phase ranging from -78.75° to 90° with discrete steps of 11.25°. After reset condition, the sampling time phase is +11.25°. The antenna phase shift evaluation is only done : - after each wake-up command (see pages 10 to 12), - or after reset (see page 7). This is necessary to obtain the best demodulator performances. In order to ensure a fast demodulator settling time after wake up, reset or a write sequence, the external capacitor CEXT is preloaded at its working voltage. This preset occurs 256µs after switching the antenna drivers on and its duration is 128µs. After wake up or reset, the preset has the same duration but begins 518µs after clock settling. After power on reset, VSUP must meet the minimum specified value, enabling the nominal operation of VDD, before the start of the preset. Otherwise the preset must be done by the user through a standby/wake-up sequence. Write function Whatever the selected configuration (see page 9), the write function is achieved by switching on/off the output drivers TD1/2. Once the drivers have been set in high impedance, the load current flows alternatively Figure 3 : Current flow when the buffers are switched off CA LA R1 RA TD1 VDD TD2 VDD ILOAD Freescale Semiconductor, Inc. For More Information On This Product, Go to: www.freescale.com |
Số phần tương tự - MC33690DW |
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Mô tả tương tự - MC33690DW |
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