Datasheet LTC4307 (Analog Devices) - 10

LTC4307
APPLICATIONS INFORMATION Live Insertion and Capacitance Buffering Application
In most applications the LTC4307 will be used with a staggered connector where V Figures 4 and 5 illustrate applications of the LTC4307 that CC and GND will be long pins. SDA and SCL are medium length pins to ensure that take advantage of the LTC4307’s Hot SwapTM , capacitance the V buffering and precharge features. If the I/O cards were CC and GND pins make contact fi rst. This will allow the precharge circuitry to be activated on SDA and SCL plugged directly into the backplane without the LTC4307 before they make contact. ENABLE is a short pin that is buffer, all of the backplane and card capacitances would pulled down when not connected. This is to ensure that add directly together, making rise-time and fall-time re- the connection between the backplane and the card’s data quirements diffi cult to meet. Placing an LTC4307 on the and clock busses is not is not enabled until the transients edge of each card, however, isolates the card capacitance associated with live insertion have settled. from the backplane. For a given I/O card, the LTC4307 drives the capacitance of everything on the card and the Figure 4 shows the LTC4307 in an application with a stag- backplane must drive only the capacitance of the LTC4307, gered connector. The LTC4307 receives its VCC voltage which is less than 10pF. from one of the long “early power” pins. Establishing Hot Swap is a trademark of Linear Technology Corporation. early power VCC ensures that the 1V precharge voltage is present at SDAIN and SCLIN before they make contact. BACKPLANE CARD BACKPLANE CONNECTOR CONNECTORS I/O PERIPHERAL CARD 1 VCC C1 0.01μF R1 R2 R3 R5 R6 10k 10k 10k 10k 10k VCC SDA SDAIN SDAOUT CARD1_SDA SCL SCLIN SCLOUT CARD1_SCL LTC4307 ENA1 ENABLE READY READY R4 GND 10k • • • I/O PERIPHERAL CARD N C2 0.01μF R8 R9 10k 10k VCC SDAIN SDAOUT CARDn_SDA SCLIN SCLOUT CARDn_SCL LTC4307 ENAn ENABLE READY R7 GND 10k 4307 F04
Figure 4. The LTC4307 in an Application with a Staggered Connector
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