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- 24th August 2008, 22:38 #1

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## tl431 pspice

What modifications are needed to convert C. Bassos TL431 Pspice model

to a TLVH431 model? The TLVH431 is the Low Voltage low current version of the TL431.

I tried the obvious switching the 2.495V to 1.24V but I get a

reference of 1.49V when I do this, it should be 1.24V.

This is the TL431 model.

Code:.SUBCKT TL431 7 6 11 V1 1 6 2.495 R1 6 2 15.6 C1 2 6 .5U R2 2 3 100 C2 3 4 .08U R3 4 6 10 G2 6 8 3 6 1.73 D1 5 8 DC D2 7 8 DC V4 5 6 2 G1 6 2 1 11 0.11 .MODEL DC D +IS=13.5N RS=25M N=1.59 + CJO=45P VJ=.75 M=.302 + TT=50.4N BV=34V IBV=1MA .ENDS ********

TL431

Code:http://www.fairchildsemi.com/ds/TL/TL431A.pdf

Code:http://www.ti.com/lit/gpn/tlvh431

- 24th August 2008, 22:38

- 25th August 2008, 08:10 #2

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## tl431 spice model

It's a functional model only. To get it working at 1.24 V, you must at least reduce the V4 limiting voltage source. And shouldn't expect, that it describes the TLVH431 behaviour unless you adjusted the functional model to the device parameters.

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- 25th August 2008, 08:10

- 25th August 2008, 13:28 #3

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## tl431 model

I found a more accurate TL431 behavioral model. Basso derives it in his second book. He provides comparisons of all the data sheet graphs, and the model reproduces them with pretty good accuracy. There doesn’t seem to be any significant difference with the LV version of the 431 other then the bias current and the reference voltage. The model doesn’t include bias current anyways.

Code:.SUBCKT TL431 a k ref C1 7 a 1n Q1 k 2 1 QN3904 R1 1 7 240 R2 7 a 6.6k Q2 k 7 a QN3904 50 D1 ref k D4mod D2 a k D2mod V1 5 a DC=2.49 D3 a 2 D3mod C4 k 2 43p G2 a 2 5 ref -250u * .MODEL QN3904 NPN AF=1.0 BF=300 BR=7.5 CJC=3.5PF CJE=4.5PF + IKF=.025 IS=1.4E-14 ISE=3E-13 KF=9E-16 NE=1.5 RC=2.4 + TF=4E-10 TR=21E-9 VAF=100 XTB=1.5 .MODEL D3mod D N=0.01 .MODEL D2mod D BV=36 CJO=4PF IS=7E-09 M=.45 N=1.3 RS=40 + TT=6E-09 VJ=.6V .MODEL D4mod D BV=100V CJO=4PF IS=7E-09 M=.45 N=2 RS=.8 + TT=6E-09 VJ=.6V * .ENDS

I have a bunch of TLVH431’s ,I use them a lot as inexpensive low current comparators and EA’s. So a reasonably accurate model would come in handy.

I’m using one for the EA in an LDO Vin = 6 -5.25V. Vo = 5.1V, 2mA TO 15mA. The FDV304P allows for worst case Drop out of 90mV (Tj 125 deg C) but with the reference and resistor tolerances’ the min input for regulation is 5.25V. I have bread boarded this and it works to 50mV drop out.

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