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SP506RB Datasheet(PDF) 9 Page - Sipex Corporation |
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SP506RB Datasheet(HTML) 9 Page - Sipex Corporation |
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9 / 30 page  9 SP505/6/7APN/03 SP505, SP506, SP507 Application Note © Copyright 2000 Sipex Corporation The SP505, SP506 and SP507 can be easily designed to support this type of configuration. Figure 6 shows a typical circuit illustrating two SP506 devices connected in a half-duplex configuration. The top circuit is dedicated to DTE and the bottom SP506 is dedicated to DCE. Note that only one device is active at any given time. For DTE, the decoder for the DCE device should be off (0000), and vice versa. During the shutdown or off state of the SP506, the driver output typically draws 100 µA of leakage current. Even with the maximum SP506 leakage current of 500 µA, the receiver input impedance would only change by 500 Ω. This is important for RS-232 since the input voltage range can be up to 15V and the typical RS-232 receiver input impedance is 5k Ω. For V.11 differential receivers, the maximum range is +7V and typical input impedance is 10k Ω. Thus for V.28 receivers, the drivers would be effectively driving into 5k Ω in parallel with the disabled receiver with 10k Ω input impedance. The resultant impedance is 3.3k Ω. For V.11 mode, the drivers will drive into either a terminated receiver of 120 Ω or unterminated receiver at 3.9k Ω. These two values in parallel with the disabled 10k Ω receiver will yield 118 Ω and 2.8kΩ, respectively, and will not degrade the V.11 driver performance. The receiver outputs are typically at 1 µA when disabled. The SP505, SP506 and SP507 adds convenience by incorporating the V.11 and V.35 termination resistors inside the device. For this type of 2-chip DTE/DCE configuration, the termination resistors would need to be disabled along with the receivers. A "0000" code into the SP505 and SP506 will automatically disable all termination networks as well as the transceivers. A "111" code into the SP507 performs the same function. In the shutdown mode, the IC will draw less than 10mA of supply current. Adding Additional Transceivers To support additional signals, the SP522 can easily attach onto the SP505, SP506 or SP507 charge pump outputs, V DD and VSS. The SP522 adds two drivers and two receivers for supporting other signals such as RI and RL. In Figure 7, the SP522 is hardwired for RS-423 or ITU-T V.10 mode. This allows for the support of RI and RL in RS-449 or V.35 modes if necessary. Schottky Diode on the SP50x Sipex requires the installation of a Schottky rectifier placed between the V CC and VDD pins of the SP50x charge pump, where the anode is connected to V CC and the cathode is connected to V DD. It is required to bootstrap the charge pump's internal circuitry during power off conditions in presence of signals or voltages through the receiver inputs or driver outputs. When placed in parallel with the charge pump capacitor, the diode will allow some of the V CC current to flow into the V DD regions of the device, which will partially bias the V DD charged regions before the device charge pump is fully functioning. This prevents biasing of V DD from other sources such as through the driver outputs or receiver inputs, typical of serial port connections to other powered-on equipment. Once the charge pump oscillator starts up and becomes functional, current flows from V DD back into V CC through the capacitor, ensuring that a rapidly rising V DD does not rise too quickly above the V CC regions before the VCC regions have become fully charged. The main characteristics of the Schottky diode necessary for this application is the forward voltage. The V F of the 1N5819 type, which is the diode recommended, is 0.6V @ 1A. Surface mount versions are available from Motorola. The MBRS130T3 from Motorola is used with our SP505, SP506, and SP507 evaluation boards. Other options are MBRS140T3 or MBRS130LT3, which are all in a "403A-03 SMB" package. The end-to-end length is 5.40mm typical and the width is 3.55mm typical. Motorola also offers the Powermite™ line, which offers the Schottky rectifiers in a 1.1mm height, 3.75mm length, and 1.90mm width surface mount package. The part numbers recommended are MBRM120LT3, MBRM120ET3, and MBRM140T3. Specifics can be found in Motorola Semiconductor's web site (http://mot-sps.com/products/index.html). The Schottky rectifiers can be found in the discrete rectifier section and datasheets can be downloaded after searching for the part number. Powermite™is a trademark of Motorola. |
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