LTC4300A-3 applicaTions inForMaTion Resistor Pull-Up Value SelectionLive Insertion and Capacitance Buffering Application The system pull-up resistors must be strong enough to Figures 3 and 4 illustrate the usage of the LTC4300A-3 provide a positive slew rate of 1.25V/µs on the SDA and in applications that take advantage of both its Hot Swap SCL pins, in order to activate the boost pull-up currents controlling and capacitance buffering features. In all of during rising edges. Choose maximum resistor value R these applications, note that if the I/O cards were plugged using the formula: directly into the backplane, all of the backplane and card R ≤ (V capacitances would add directly together, making rise- CC(MIN) – 0.6)(800,000)/C and fal time requirements difficult to meet. Placing a where R is the pull-up resistor value in ohms, VCC(MIN) LTC4300A-3 on the edge of each card, however, isolates is the minimum VCC voltage and C is the equivalent bus the card capacitance from the backplane. For a given I/O capacitance in picofarads (pF). card, the LTC4300A-3 drives the capacitance of every- In addition, regardless of the bus capacitance, always thing on the card and the backplane must drive only the choose R ≤ 16k for V capacitance of the LTC4300A-3, which is less than 10pF. CC = 5.5V maximum, R ≤ 24k for VCC = 3.6V maximum. The start-up circuitry requires logic high voltages on SDAOUT and SCLOUT to connect the backplane to the card, and these pull-up values are needed to overcome the precharge voltage. BACKPLANE BACKPLANE CONNECTOR I/O PERIPHERAL CARD 1 VCC2 C1 R1 R2 R7 R8 0.01µF 10k 10k 10k 10k V V V CC CC CC2 SDAOUT CARD_SDA SDA SDAIN LTC4300A-3 SCLOUT CARD_SCL SCL SCLIN GND ENABLE C2 0.01µF R3 ENA1 10k I/O PERIPHERAL CARD 2 C3 R4 R5 0.01µF 10k 10k V V CC CC2 SDAOUT CARD2_SDA SDAIN LTC4300A-3 SCLOUT CARD2_SCL SCLIN GND ENABLE C4 0.01µF R6 ENA2 10k 4300a3 F03 Figure 3. The LTC4300A-3 in a PCI Application Where All the Pins Have the Same Length.ENABLE Should Be Held Low Until All Transients Associated with the Live Insertion Have Settled 4300a3fa 9 Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Package Description Revision History Related Parts Typical Application
