Part Number:TL431
Hello,
Background:
I am designing signal conditioning circuits that level shifts from 3.3 or 5.25V to 15V and from 15V to 3.3 or 5.25V (for interfacing between PXI digital I/O and a unit under test (UUT)). The connections will be configurable within the product, so I want to protect the inputs of my circuitry against over-voltage in case incorrect connections are made. On the low voltage side (3.3 or 5.25), I am using an input resistor (10k) connected to the anode of a low capacitance diode (2pF) with collector tied to the 3.3 or 5.25 rail. Assuming worst case of all inputs pulled to +15V, the 1.15mA per input adds up quickly for the many channels I'm using.
I want to use the TL431IB for its accuracy, but need to buffer its output to sink < 200mA. So, I have designed a simple NPN/PNP push-pull buffer w/ a 10uF output cap as shown here.
Image may be NSFW.
Clik here to view.
R2 (100 ohms) is used to allow limited control of the output when the base/emitter junctions are "off".
Based on the TL431 data sheet, I believe the output cap in series with R2 is OK.
Also, The JP11, R3 & R5 resistors are to allow for choosing the 3.3 or 5.25V output.
Question:
Are there any "red flag" concerns to which I should be paying attention?
Including for example: looking at data sheets for some regulators, diodes are recommended for certain conditions (e.g. turn off), such as shown in the following excerpt from the LM117 datasheet. Would this be a concern for my circuit?
Image may be NSFW.
Clik here to view.
Any suggestions or warnings will be appreciated.
- James
