| Member Comments |
|
|
|
|
Scott_T
- I2C level translation
|
(no rating)
2008-08-13 |
|
Because IIC outputs just pull low, do you actually need level translation to connect IIC between two chips with different VDD? Don't you just have pull up resistors on each line to the lowest of the two supply voltages? You would have to check that with the chosen resistor pull-up goes above the high threshhold and each output can pull the line below the low threshhold.
|
|
|
|
|
isa_2006
- I2C level translation
|
(no rating)
2008-09-16 |
|
pull resistor is sufficient only if the IO of the device with low VDD tolerates the highest VDD. for example while interfacing a 3.3V device to a 5V device, the IO pin of 3.3V device must be 5V tolerant.
|
|
|
|
|
therese
- Re: I2C level
|
(no rating)
2008-09-16 |
Scott_5, ISA,
The reason for which the solution proposed will not work is because the SDA and SDL lines of the I2C interface are bidirectional for all parts, both master and slaves. That means that need to act both as inputs and outputs at different times in the interface protocol. Also, the VIH and VIL of the devices used in a system can be of two types, fixed input levels or VDD related input levels (VIH and VIL are fractions of VDD).
In a mixed VDD voltage system (usually some parts powered by a VDD supply higher than the master microcontroller) a simple pull-up resistor to the lowest VDD for each line will not satisfy in most cases the VIH requirements of the inputs of the higher VDD powered parts. A pull-up to the higher VDD will probably violate the absolute maximum rating of the parts with the lower VDD specification.
In those cases a bidirectional level translator is a good solution.
Download the Philips I2C Bus specification document.
See Table 4 (Characteristics of the SDA and SCL I/O stages for F/S-mode I2C-bus devices) in "The I2C-Bus Specification, Version 2.1, January 2000": http://www.nxp.com/acrobat_download/literature/9398/39340011.pdf
Regards,
Applications Engineering
Technical Support
Maxim
|
|
|
|
|
Curt
- Interfacing Issues
|
(no rating)
2009-01-28 |
|
Are pull up resistors needed when using the max3378 for spi communications or can 3378 be connected directly between microcontroller and spi device?
|
|
|
|
|
Hanif
- Hanif
|
(no rating)
2009-02-05 |
Curt,
The MAX3378E features 10k-ohm internal pull-up resistors for each of the I/O VL and I/O Vcc lines to their respective power supplies. Thus, you can connect directly.
Regards,
Applications Engineering
Technical Support
MAXIM
|
|
|
|
|
| Your Comments | |
|
Login or register to post a comment.
|