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ST75C540 数据表(PDF) 79 Page - STMicroelectronics |
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ST75C540 数据表(HTML) 79 Page - STMicroelectronics |
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79 / 84 page  XVIII - PCB DESIGN GUIDELINES Performances of the FAX modem depends on the ST75C530/540 intrinsic performances and on the proper PC board layout. All aspects of the proper engineering practices, for PC board design, are beyond the scope of this paragraph. We recommend the following points : - in a 4-layer PC board : Separated digital ground and analog ground, connected together at one point, as close as possible to the ST75C530/540, - in a 2-layer PC board : Provide a ground grid in all spacearoundandundercomponentson bothsides of the band and connect to avoid small islands, - both AGNDR and AGNDT must be connected with very low impedance to a single point, (see Chapter I.6, Power Supply), - the four 2.2nF capacitors connected to the RxA and MIC1, MIC2, MIC3 Pins must be as close as possible to them, - thetwo100nFcapacitorsconnectedtotheVREFP and VREFN pins must be as close as possible to them, - analog and digital supplies must be connected together,at a single point, as close as possibleto the chip. 15 ADC MUTE DAC Line HYBRID TxA1 TxA2 RxA ADC 14 11 10 MIC3 8 MIC1 9 MIC2 79 SPK2 78 MUTE 77 SPK3 76 MUTE 2 SPK1 1 MUTE [0..-30]dB Step 3dB DAC ATT_SPK ATT_LOC ATT_TX 4 TONES GENERATOR DG DTMF DETECTOR 16 TONE DETECTORS 4 TONE DETECTORS V.21 FLAG DETECTOR RING DETECTOR DUAL RAM INTERFACE DG Programmable Attenuation Addition of Signals Automatic Gain Figure 49 : Tone Mode (TONE) 15 ADC MUTE DAC Line HYBRID TxA1 TxA2 RxA ADC 14 11 10 MIC3 8 MIC1 9 MIC2 79 SPK2 78 MUTE 77 SPK3 76 MUTE 2 SPK1 1 MUTE [0..-30]dB Step 3dB DAC ATT_SPK ATT_LOC ATT_TX 4 TONES GENERATOR DG DTMF DETECTOR 6 TONE DETECTORS 4 TONE DETECTORS V.21 FLAG DETECTOR UART DUAL RAM INTERFACE DG Programmable Attenuation Addition of Signals Automatic Gain RING DETECTOR V.23 DEMODULATOR Figure 50 : Tone Mode with Caller ID (TONECID) XIX - APPENDIX A : MODES OF OPERATION ST75C530 - ST75C540 79/84 |
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