| ??? 06/30/08 03:47 Read: times |
#156303 - The BSS138... Responding to: ???'s previous message |
The BSS138 is barely suitable for this application. When the 1.8V side drives the I/O low the BSS138 will experience a Vgs drive of 1.8V minus the Vol of the driving logic. A look at the BSS138 data sheet will show this is barely inside the spec for the part.
When the 5V side drives its I/O low the BSS138 gets a VGS that is intially 1.8V minus the Vf of the body diode minus the Vol of the driver on that side. Not enough to provide suitable drive for the FET. As a matter of fact this type of circuit works well with a low side voltage of 3.3V but not 1.8V. For low voltage operation you need to look at a part specifically designed for translating 1.8V or lower up to 5V (or the other way ... or bi-directionally ... depending upon your needs). Michael Karas |
| Topic | Author | Date |
| 1.8<-->5V Level | 01/01/70 00:00 | |
| TI and NXP | 01/01/70 00:00 | |
| Any specific part number? | 01/01/70 00:00 | |
| pssibly | 01/01/70 00:00 | |
| Ok but about part | 01/01/70 00:00 | |
| Try digikey | 01/01/70 00:00 | |
| I read about some MOSFETs that switch at <1.5V | 01/01/70 00:00 | |
| why fiddle when there are dedicated chips? | 01/01/70 00:00 | |
| It depends on how many he needs, doesn't it? | 01/01/70 00:00 | |
| not really | 01/01/70 00:00 | |
| and what's price and availability in small quantit | 01/01/70 00:00 | |
| Any discrete solution | 01/01/70 00:00 | |
| a transistor ? | 01/01/70 00:00 | |
| nxp ANSWER | 01/01/70 00:00 | |
| NXP Picogates | 01/01/70 00:00 | |
| I read about some MOSFETs that switch at <1.5V | 01/01/70 00:00 | |
| Schematic here | 01/01/70 00:00 | |
| The BSS138... | 01/01/70 00:00 | |
| another part | 01/01/70 00:00 | |
| Very bad choice | 01/01/70 00:00 | |
| why, OH why ... | 01/01/70 00:00 | |
| 8 lines | 01/01/70 00:00 | |
| I listed 1, 2 and 6 line chips in a former post | 01/01/70 00:00 | |
| why not | 01/01/70 00:00 | |
| ZXM61N02 | 01/01/70 00:00 | |
BSS138 | 01/01/70 00:00 |