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TNETV2685ZUT11 数据表(PDF) 49 Page - Texas Instruments |
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TNETV2685ZUT11 数据表(HTML) 49 Page - Texas Instruments |
49 / 191 page TMS320DM647 TMS320DM648 www.ti.com SPRS372H – MAY 2007 – REVISED APRIL 2012 3.3 Pullup/Pulldown Resistors Proper board design should specify that input pins to the device always be at a valid logic level and not floating. This may be achieved via pullup/pulldown resistors. The device features internal pullup (IPU) and internal pulldown (IPD) resistors on most pins to eliminate the need, unless otherwise noted, for external pullup/pulldown resistors. An external pullup/pulldown resistor must be used in the following situations: • Boot and Configuration Pins: If the pin is both routed out and in high-impedance mode, an external pullup/pulldown resistor must be used, even if the IPU/IPD matches the desired value/state. • Other Input Pins: If the IPU/IPD does not match the desired value/state, use an external pullup/pulldown resistor to pull the signal to the opposite rail. If the boot and configuration pins are both routed out and in high-impedance mode, it is recommended that an external pullup/pulldown resistor be used. Although internal pullup/pulldown resistors exist on these pins and they may match the desired configuration value, providing external connectivity can help specify that valid logic levels are latched on these important boot configuration pins. In addition, applying external pullup/pulldown resistors on the boot and configuration pins adds convenience to the user in debugging and flexibility in switching operating modes. Tips for choosing an external pullup/pulldown resistor: • Select a resistor with the largest possible resistance • Calculate the worst-case leakage current that flows through this external resistor. Worst-case leakage current can be calculated by adding up all the leakage current at the pin—e.g., the input current (II) from the device, and leakage current from the other device(s) to which this pin is connected. • Specify that the voltage at the pin stays well within the low-/high-level input voltages (VIL or VIH) when worst-case leakage current is flowing through this external resistor. – To oppose an IPU and pull the signal to a logic low, the voltage at the pin must stay well below VIL. – To oppose an IPD and pull the signal to a logic high, the voltage at the pin must stay well above VIH. For most systems, a 1-k Ω resistor can be used to oppose the IPU/IPD while meeting the above criteria. Users should confirm this resistor value is correct for their specific application. For most systems, a 20-k Ω resistor can be used to complement the IPU/IPD on the boot and configuration pins while meeting the above criteria. Users should confirm this resistor value is correct for their specific application. For more detailed information on input current (II), and the low-/high-level input voltages (VIL and VIH) , see Section 5.3, Electrical Characteristics Over Recommended Ranges of Supply Voltage and Operating Temperature. For the internal pullup/pulldown resistors for all device pins, see the peripheral/system-specific terminal functions table. Copyright © 2007–2012, Texas Instruments Incorporated Device Configuration 49 Submit Documentation Feedback Product Folder Link(s): TMS320DM647 TMS320DM648 |
类似零件编号 - TNETV2685ZUT11 |
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类似说明 - TNETV2685ZUT11 |
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