| ??? 08/16/08 19:56 Read: times |
#157514 - P-Channel Enhancement Mode Better Responding to: ???'s previous message |
For the diagram in the original posting by Koosha the switch is shown in the VCC line of the target MCU. For switching the power in this type of circuit a P-Channel Enhancement Mode FET would be a far better choice as shown below:
 A suitable part may be the FDC638 from Fairchild. The data sheet is here: FDC638 The reason a P-Channel part is suitable here is that the part can become fully ON when the Gate is pulled toward GND by the output pin of the main MCU. This applies a VGS of nearly 5V to the FET and can ensure that the suggested part is turned on to a very low RDS. If an N-Channel FET is chosen, as suggested by Mr Erlacher, it is necessary to provide a gate drive voltage well above the +5V level to ensure that the device is fully powered on if the switch is placed in the VCC line of the target MCU. Now while this is possible if you have a higher voltage source available it is also then necessary to provide an additional stage of circuitry between the MCU output and the n-FET gate drive so that the output is not exposed to voltages over the VCC level of the master MCU. Michael Karas |
| Topic | Author | Date |
| How to turn on/off another MCU | 01/01/70 00:00 | |
| Low-power mode? | 01/01/70 00:00 | |
| not a power consumption issue | 01/01/70 00:00 | |
| correction | 01/01/70 00:00 | |
| Logic MOSFET | 01/01/70 00:00 | |
| P-Channel Enhancement Mode Better | 01/01/70 00:00 | |
| that's why they make logic MOSFET's | 01/01/70 00:00 | |
| Makes No Difference | 01/01/70 00:00 | |
| Perhaps you should try a logic-MOSFET | 01/01/70 00:00 | |
| It Still Makes No Difference | 01/01/70 00:00 | |
| Maybe it's the load current | 01/01/70 00:00 | |
| Richard........................... | 01/01/70 00:00 | |
| I wouldn't say that ... | 01/01/70 00:00 | |
| possibly simpler idea | 01/01/70 00:00 | |
Thank you all, | 01/01/70 00:00 |