Keywords: backup power supplies, microprocessor supervisors, low voltage, MOSFET switches
A few microprocessor supervisor ICs incorporate a voltage detector with an internal switch. Unfortunately, due to technology limitations, the internal switch has an impedance of 1 ohm or more, limiting the current handling to a couple of hundred milliamps. When power supplies need to supply several amps, external switches need to be added.
The circuit shown in the attached diagram depicts how to connect external switches to a microprocessor supervisor.
The BATT ON pin is high whenever the chip has detected a power failure and switches to the backup supply. Transistor T1 bypasses the internal switch for the main supply. Transistor T2 is an inverter, blocking T3. When the main power fails, BATT ON blocks T1, and enables T3, via T2. The external diodes are optional, to prevent glitches during switchover.
The supervisor chip can be a MAX6367, for instance, if a preset voltage for switching is required (in this case 3.08V). For non-standard voltages, the MAX794 can be used. Its voltage can be set with an external voltage divider.
Figure 1. Power backup switch.
|EE-Mail||Subscribe to EE-Mail and receive automatic notice of new documents in your areas of interest.|
|Download||Download, PDF Format|
|© , Maxim Integrated Products, Inc.|
APPLICATION NOTE 3323,AN3323, AN 3323, APP3323, Appnote3323, Appnote 3323
Unfortunately, we are unable to place your order due to restrictions on your account. Please contact customer support.
Sorry, but we are unable to process sample requests from non-business or non-educational e-mail addresses via this site. Your options are :
Thank you for your interest in Maxim
Thank You for interest in Maxim Integrated. Our free samples program limits the quantities that we can provide to each customer per calendar year.If you feel that you have received this message in error, please contact firstname.lastname@example.org. Alternatively, you can click here to place an order.
|Part Number||Description||Key Advantages|
Are you sure you want to Request Company Account?