Other Parts Discussed in Thread: TLV431, TLVH431
Hello,
The LM4051-N datasheet in its latest version dated 2018 is the cause of much confusion. I have used the adjustable version as a replacement for the temporarily unavailable TLV431, based upon figure 20 and the accompanying equation 7. However, it turns out that equation 7 should have been written: V0 = (1+(R2/R1))*Vref rather than V0=(1+(R1/R2))*Vref. This is because the reference voltage of the device is developed between the cathode (positive) and feedback terminals rather than between the feedback terminal and the anode, as is the case for the TLV431.
The incorrect nature of equation 7 is confirmed by reference to the functional block diagram presented in paragraph 8.2, which indicates the reference voltage developed between the positive terminal (the cathode) and the feedback terminal.
The actual observed circuit behavior of the LM4051-N adjustable version confirms the above claims, and indicates that the selection of the LM4051-N adjustable version as a replacement for the TLV431 in the simple configuration of figure 20 would require the resistor values to be transposed relative to the same circuit based upon the TLV431.
As our OEM customer would not like to switch the resistor values round when using the LM4051-N adjustable version as a second source, we cannot consider it to be a suitable replacement for the TLV431 and will therefore need to find a different source until the TLV431 eventually reappears on the market.
At any rate, please confirm my above claims and ensure that if you agree then equation 7 of the LM4051-N datasheet should be corrected as I have recommended. In that case, equation 8, which is a more accurate rendering of equation 7, is similarly corrected.
Best regards,
David Drori
