| ??? 12/17/07 08:49 Read: times Msg Score: +5 +4 Informative +1 Good Answer/Helpful |
#148358 - There Are Proper Circuits for This Responding to: ???'s previous message |
TI, NXP and MAXIM all make a whole series of repeater parts that can be used as voltage level converters and bidirectional re-drivers for I2C bus lines. Look for part numbers PCA9515 and PCA9511 for several examples.
There is a far simpler bi-directional I2C buffer circuit that can be made with a single N-FET. The place I work tends to use these discrete circuit level translators for I2C busses and conversion from 5V <-> 3.3V and for isolation between standby voltage rails and switched voltage rail segments of the bus. Of particular note is that one can get dual N-FETS in small SOT-363 packages and build a buffer/translator for an I2C bus with one chip and a few discretes. Note that the pullup resistors shown are those needed already for the I2C bus. These are used because the BOM cost on a high volume board is about 1/4 the cost of a PCA9515 and 1/10 the cost of a PCA9511. 
Michael Karas |
| Topic | Author | Date |
| Bidirectional level translation with transistors | 01/01/70 00:00 | |
| why use discretes whern a cheap chip exist. | 01/01/70 00:00 | |
| ~0.3us worst case | 01/01/70 00:00 | |
| 74LVC4245 is not "automatically" bidir... | 01/01/70 00:00 | |
| 74LVC4245 has 24 leads | 01/01/70 00:00 | |
| no overkill | 01/01/70 00:00 | |
| none of these are bidir | 01/01/70 00:00 | |
| 24 leads | 01/01/70 00:00 | |
| and what? | 01/01/70 00:00 | |
| What! | 01/01/70 00:00 | |
| but the 24 pins don't provide equivalent... | 01/01/70 00:00 | |
| Still less :) | 01/01/70 00:00 | |
| No steep egdes! | 01/01/70 00:00 | |
| time to get rid of that superfast logic, Kai :-) | 01/01/70 00:00 | |
| CUte circuit - does NOT work levels above 8 volts | 01/01/70 00:00 | |
| There Are Proper Circuits for This | 01/01/70 00:00 | |
| A detailed analysis of this technique can be ... | 01/01/70 00:00 | |
Do I need to say more :) | 01/01/70 00:00 |