TECHNICAL DATA TL431Z Programmable Precision Reference Pin Connections Description The TL431Z is a three-terminal adjustable regulator series with a guaranteed thermal stability over applicable temperature ranges. The output voltage may be set to any value between Vref (approximately 2.5 volts) and 40 volts with two external resistors. These devices have a typical dynamic output impedance of 0.2Ω. Active output circuitry provides a very sharp turn-on characteristic, making these devices excellent replacement for zener diodes in many applications.The TL431Z is characterized for operation from 25oC to +85oC. TO-92 SOP-8 ANODE REFERENCE CATHODE SOT-23 SOT-89 Features • Programmable Output Voltage to 40V • Low Dynamic Output Impedance 0.2Ω • Sink Current Capability of 0.1 mA to 100 mA • Equivalent Full-Range Temperature Coefficient of 50 ppm/oC • Temperature Compensated for Operation over Full Rated Operating Temperature Range • Low Output Noise Voltage • Fast Turn on Response • TO-92, SOP- 8, SOT-23, SOT-89 packages Ordering Information Product Number TL431ZCLF TL431ZCLS TL431ZCD TL431ZCS TL431ZCP TL431ZALF TL431ZALS TL431ZAD TL431ZAS TL431ZAP TL431ZLF TL431ZLS TL431ZD TL431ZS TL431ZP Reference Input Voltage Package TO-92 0.5% 8-SOP SOT-23 SOT-89 TO-92 1% 8-SOP SOT-23 SOT-89 TO-92 2% 8-SOP SOT-23 SOT-89 Rev. 01 TL431Z Symbol Functional Block Diagram Equivalent Schematic ABSOLUTE MAXIMUM RATINGS (Operating temperature range applies unless otherwise specified) Characteristic Cathode Voltage Cathode Current Range (Continuous) Reference Input Current Range o Power Dissipation at 25 C: SOP, TO – 92 Package (RθJA = 178oC/W) SOT Package (RθJA = 625oC/W) Junction Temperature Range Operating Temperature Range Storage Temperature Range Symbol Value Unit VKA 44 V IK -100 ~ 150 mA IREF 0.05 ~ 10 mA 0.7 0.2 W W PD TJ Tg Tstg -25 ~ 150 o -25 ~ 85 o -65 ~ 150 o C C C RECOMMENDED OPERATING CONDITIONS Characteristic Cathode to Anode Voltage Cathode Current Symbol Min VKA IK Typ Max Unit VREF 40 V 0.5 100 mA Rev. 01 TL431Z ELECTRICAL CHARACTERISTICS (Ta = 25oC, VKA = VREF, IK = 10mA unless otherwise specified) Characteristic Reference Input Voltage Deviation of Reference Input Voltage Over Full Temperature Range Ratio of Change in Reference Input Voltage to the Change in Cathode Voltage Reference Input Current Deviation of Reference Input Current Over Full Temperature Range Symbol Test Condition VREF VKA = VREF, IK = 10mA Min Typ Max TL431Z (2%) 2.440 2.495 2.550 TL431Z-A (1%) 2.470 2.495 2.520 TL431Z-C (0.5%) 2.482 2.495 2.508 VREF(dev) Tmin ≤ Ta ≤ Tmax ∆V REF ∆V K A Unit V 3 17 MV ∆VKA = 10V-VREF -1.4 -2.7 ∆VKA = 36V- 10V -1.0 -2.0 mV/V IREF R1 = 10KΩ, R2 = ∞ 1.8 4 ㎂ IREF(dev) R1 = 10KΩ, R2 = ∞ 0.4 1.2 ㎂ 0.25 0.5 mA Minimum Cathode Current for Regulation IK(min) Off-State Cathode Current IK(off) VKA = 40 V, VREF = 0 0.17 0.9 ㎂ Dynamic Impedance ZKA IK = 10mA to 100 mA , f ≤ 1.0KHz 0.27 0.5 Ω Note : 1. The deviation parameter ∆Vref is defined as the difference between the maximum and minimum values obtained over the full operating ambient temperature range that applies The average temperature coefficient of the reference input voltage, aVref is defined as: αVref can be positive or negative depending on whether Vref Min or Vref Max occurs at the lower ambient temperature. (Refer to Figure 6.) 2. The dynamic impedance ZKA is defined as When the device is programmed with two external resistors, R1 and R2, (refer to Figure 2) the total dynamic impedance of the circuit is defined as: Rev. 01 TL431Z TEST CIRCUITS Fig.1. Test Circuit for VKA = VREF Fig.2. Test Circuit for VKA ≥ VREF TL431Z TL431Z Fig.3. Test Circuit for Ioff TL431Z Figure 4. Cathode Current versus Cathode Voltage Figure 5. Cathode Current versus Cathode Voltage Figure 6. Reference Input Voltage versus Ambient Temperature Figure 7. Reference Input Current versus Ambient Temperature Rev. 01 TL431Z Figure 8. Change in Reference Input Voltage versus Cathode Voltage Figure 9. Off–State Cathode Current versus Ambient Temperature Figure 10. Dynamic Impedance versus Frequency Figure 11. Dynamic Impedance versus Ambient Temperature Figure 12. Open–Loop Voltage Gain versus Frequency Figure 13. Spectral Noise Density Rev. 01 TL431Z Figure 14. Pulse Response Figure 15. Stability Boundary Conditions Figure 16. Test Circuit For Curve A of Stability Boundary Conditions Figure 17. Test Circuit For Curves B, C, And D of Stability Boundary Conditions TYPICAL APPLICATIONS Figure 18. Shunt Regulator Figure 19. High Current Shunt Regulator Rev. 01 TL431Z Figure 20. Output Control for a Three–Terminal Fixed Regulator Figure 21. Series Pass Regulator Figure 22. Constant Current Source Figure 23. Constant Current Sink Figure 24. TRIAC Crowbar Figure 25. SRC Crowbar Rev. 01 TL431Z Figure 26. Voltage Monitor Figure 27. Single–Supply Comparator with Temperature–Compensated Threshold Figure 28. Linear Ohmmeter Figure 29. Simple 400 mW Phono Amplifier Figure 30. High Efficiency Step–Down Switching Converter Rev. 01 TL431Z APPLICATIONS INFORMATION The TL431Z is a programmable precision reference which is used in a variety of ways. It serves as a reference voltage in circuits where a non–standard reference voltage is needed. Other uses include feedback control for driving an optocoupler in power supplies, voltage monitor, constant current source, constant current sink and series pass regulator. In each of these applications, it is critical to maintain stability of the device at various operating currents and load capacitances. In some cases the circuit designer can estimate the stabilization capacitance from the stability boundary conditions curve provided in Figure 15. However, these typical curves only provide stability information at specific cathode voltages and at a specific load condition. Additional information is needed to determine the capacitance needed to optimize phase margin or allow for process variation. A simplified model of the TL431Z is shown in Figure 31. When tested for stability boundaries, the load resistance is 150 Ω. The model reference input consists of an input transistor and a dc emitter resistance connected to the device anode. A dependent current source, Gm, develops a current whose amplidute is determined by the difference between the 1.78 V internal reference voltage source and the input transistor emitter voltage. A portion of Gm flows through compensation capacitance, CP2. The voltage across CP2 drives the output dependent current source, Go, which is connected across the device cathode and anode. Model component values are: Vref = 1.78 V Gm = 0.3 + 2.7 exp (–IC/26 mA) where IC is the device cathode current and Gm is in mhos 2 Go = 1.25 (Vcp ) µmhos. Resistor and capacitor typical values are shown on the model. Process tolerances are ±20% for resistors, ±10% for capacitors, and ±40% for transconductances. An examination of the device model reveals the location of circuit poles and zeroes: In addition, there is an external circuit pole defined by the load: Also, the transfer dc voltage gain of the TL431Z is: Example 1: The resulting transfer function Bode plot is shown in Figure 32. The asymptotic plot may be expressed as the following equation: The Bode plot shows a unity gain crossover frequency of approximately 600 kHz. The phase margin, calculated from the equation, would be 55.9 degrees. This model matches the Open–Loop Bode Plot of Figure 12. The total loop would have a unity gain frequency of about 300 kHz with a phase margin of about 44 degrees. Rev. 01 TL431Z Figure 31. Simplified TL431Z Device Model Figure 32. Example 1 Circuit Open Loop Gain Plot Figure 33. Example 2 Circuit Open Loop Gain Plot Example 2. IC = 7.5 mA, RL = 2.2 kΩ, CL = 0.01 µF. Cathode tied to reference input pin. An examination of the data sheet stability boundary curve (Figure 15) shows that this value of load capacitance and cathode current is on the boundary. Define the transfer gain. The DC gain is: With three poles, this system is unstable. The only hope for stabilizing this circuit is to add a zero. However, that can only be done by adding a series resistance to the output capacitance, which will reduce its effectiveness as a noise filter. Therefore, practically, in reference voltage applications, the best solution appears to be to use a smaller value of capacitance in low noise applications or a very large value to provide noise filtering and a dominant pole rolloff of the system. G = GMRGMGoRL = (2.323)(1.0 M)(1.25 µ)(2200) = 6389 = 76 dB The resulting open loop Bode plot is shown in Figure 33. The asymptotic plot may be expressed as the following equation: Note that the transfer function now has an extra pole formed by the load capacitance and load resistance. Note that the crossover frequency in this case is about 250 kHz, having a phase margin of about –46 degrees. Therefore, instability of this circuit is likely. Rev. 01 TL431Z Package Dimensions D SUFFIX SOIC (MS - 012AA) Dimension, mm A 8 5 B H 1 G P 4 D K MIN MAX A 4.80 5.00 B 3.80 4.00 C 1.35 1.75 D 0.33 0.51 F 0.40 1.27 R x 45 C -T- Symbol SEATING PLANE J F 0.25 (0.010) M T C M NOTES: 1. Dimensions A and B do not include mold flash or protrusion. 2. Maximum mold flash or protrusion 0.15 mm (0.006) per side for A; for B ‑ 0.25 mm (0.010) per side. M G 1.27 H 5.72 J 0° 8° K 0.10 0.25 M 0.19 0.25 P 5.80 6.20 R 0.25 0.50 Rev. 01 TL431Z TO-92 Rev. 01 TL431Z Rev. 01 TL431Z Rev. 01