Hi,
I am using buffers SN74LVT245B and SN74BCT760 for VME interface. Please let me know the input capacitance for these devices when these are in high impedance state ( OE is high ).
Thanks & Regards
Madhu Sharma
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Hi,
I am using buffers SN74LVT245B and SN74BCT760 for VME interface. Please let me know the input capacitance for these devices when these are in high impedance state ( OE is high ).
Thanks & Regards
Madhu Sharma
Hi Madhu,
The datasheet specifies for SN74LVT245B that the Cio which is the capacitance you are looking for to be 9 pF.
The datasheet specifies for SN74BCT760 that the Ci which is the capacitance you are looking for to be 10 pF.
Please note that the reason the first device has IO instead of O like the second device is because the SN74LVT245B device outputs also function as inputs.
Thanks,
Daniel
Hi,
Thanks for the quick reply.
As per my understanding, Cio / Co represents the input and output capacitance when the device is active. But my question is different. Please refer the attached image. When Buffer B present in one board is high impedance state, some other Buffer A, present in other board will drive the line. In that case, what will be the load capacitance of output line of buffer B seen by A?
Thanks & Regards
Madhu Sharma K
Hi Madhu,
Below is the definition of output capacitance that TI defines. I believe this is the capacitance you are searching for.
Link to applications note: www.ti.com/.../szza036c.pdf
The output capacitance will be when the device is in High Z mode.
Thanks,
Daniel
Hi Daniel,
I'm using the buffer to drive the VME bus and since VME bus has 21 board slots and includes long traces, the load capacitance will be large, about 400pF. Please let me know whether load capacitance of this range would disturb the normal operation.
Thanks & Regards
Madhu Sharma K
Hai Daniel,
Thanks for the reply.
I have gone through datasheet of SN74VMEH22501 and since i need industrial grade components, I am planning to use SN74VMEH22501A. But there is one more part, with part number SN74VMEH22501A-EP. What are the differences between these two?
Also, When I use SN74VMEH22501A in Transparent mode, since i am not using the clock signals, how should i connect the two clock pins ( CLKAB & CLKBA)?
Regards
Madhu Sharma
Hey Madhu,
EP stands for enhanced product and generally refers to an increase in Temperature operation range.
As far as how to connect the CLK pins since you aren't using them refer to the highlighted portion of the datasheet. They should be tied to GND or Vcc to ensure proper device operation.
Thanks,
Daniel Hartung
Hi Daniel,
1) The datasheet tells to connect the control pins to VCC or GND. While connecting to GND, Can I Connect directly or should I use a resistor?
2) In VME bus, there are some signals which are Open drain/collector. Can you please suggest me any such buffers which are designed/tested for VME interface?
Regards
Madhu Sharma
Hey Madhu,
1) I refer you to page 2 on the datasheet:
2) We don't have any buffer/drivers specifically made for VME interface, but I imagine that you can find a buffer/driver that is suitable for your application in our buffer/driver products here:
http://www.ti.com/lsds/ti/logic/non-inverting-buffer-driver-products.page
Thanks,
Daniel
Hi Daniel,
For SN74VMEH22501A:
1) I am planning to connect the data lines to all the 10 pins. Can I short 1A and 1Y lines ( and 2A and 2Y) to make the 1 bit transceivers bidirectional?
2) If 1A and 1Y are shorted what is the differences ( based on performance) between 8 bit UBTs and 1 bit transceivers? can those be used as bus transceivers?
3) Will there be any harm to the device if a pull up is connected for the output pins ( 1B, 2B and 3B pins)?
Regards
Madhu Sharma