1.24V Low-Voltage Adjustable Precision Shunt Regulator NIKO-SEM L431L GENERAL DESCRIPTION FEATURES The L431L is a three-terminal adjustable shunt regulator utilizing an accurate 1.24V band gap reference. The output voltage can be set to any value between 1.24V (VREF) to 18V with two external resistors as shown in the typical application circuit. The device exhibit a wide operating current range of 0.2 to 100 mA with a typical dynamic impedance of 0.25Ω. Active output circuitry provides a very sharp turn-on characteristic, making the L431L excellent replacements for low-voltage zener diodes in many applications, including on-board regulation and adjustable power supplies. When used with an opto-coupler, the L431L is ideal voltage reference in isolated feedback circuits for 3.3V switching-mode power supplies. The L431L shunt regulator is available in two voltage tolerances (0.5% & 1.0%) and three package options (TO-92, SOT-23-3 and SO-8). z Internal amplifier with 100 mA capability z Programmable output voltage to 18V z 0.25Ω typical output impedance z Pin to pin compatible with TLV431A, TS431, SC431L & AS432 z Trimmed bandgap design 0.5% & 1.0% with three package options z Low output noise APPLICATIONS z Linear regulator controller z Precision voltage reference z Switching power supplies z Battery operating equipment z Instrumentation z PCs, Computer disk drives SYMBOL & BLOCK DIAGRAM Cathode (K) Reference (R) + Cathod (K) - Reference (R) 1.24 Vref Anode (A) Anode (A) SYMBOL FUNCTIONAL BLOCK DIAGRAM 1 APR-25-2002 NIKO-SEM 1.24V Low-Voltage Adjustable Precision Shunt Regulator L431L ABSOLUTE MAXIMUM RATINGS PARAMETER VALUE Cathode-Anode Reverse Breakdown Voltage - VKA Anode-Cathode Forward Current - IAK Operating Cathode Current - IKA Reference Input Current - IREF Storage Temperature Range - TSTG Junction Temperature - TJ Lead Temperature (Soldering, 10 Seconds) - TL Continuous Power at 25 °C - PD TO-92 SOIC-8 SOT-23 RECOMMENDED CONDITIONS Parameter Cathode Voltage (VKA) Cathode Current (IK) Rating VREF to 18V 10 mA 20V 1A 100 mA 1 mA -65 to +150 °C 150 °C 300 °C 700 mW 650 mW 200 mW TYPICAL THERMAL RESISTANCES Package TO-92 SOIC-8 SOT-23 Typ. De-rating θJA θJC 160 °C/W 80 °C/W 6.3 mW/°C 175 °C/W 45 °C/W 5.7 mW/°C 575 °C/W 150 °C/W 1.7 mW/°C ELECTRICAL SPECIFICATIONS (Ambient temperature must be derated base on power dissipation and package thermal characteristics. The conditions are: VKA = VREF and IK = 10 mA unless otherwise stated) PARAMETER Output Voltage - VREF TEST TYP MAX UNITS CIRCUIT TA = 25 °C, L432 (0.5%) 1.234 1.240 1.246 V 1 TA = 25 °C, L432 (1%) 1.228 1.240 1.252 mV VKA = VREF to 15V 28 50 2 mV IK = 1 to 100 mA 3.9 6 1 mV 0 < TJ < 105 °C 5 12 1 µA 2.3 6 1 TEST CONDITIONS Line Regulation - ∆VREF Load Regulation - ∆VREF Temperature Deviation - ∆VREF Reference Input Current - IREF Reference Input Current 0 < TJ < 105 °C Temperature Coefficient - ∆IREF Minimum Cathode Current for Regulation - IK(MIN) Off State Leakage - IK(MIN) VREF = 0V, VKA = 15V Dynamic impedance VKA = Vref, f ≦ 1kHz IK = 0.1 mA to 100 mA 2 MIN 0.14 0.6 µA 1 0.2 1 mA 1 40 0.25 500 0.4 nA Ω 3 1 APR-25-2002 1.24V Low-Voltage Adjustable Precision Shunt Regulator NIKO-SEM L431L TEST CIRCUITS VIN VKA I REF IK VIN VKA R1 I REF IK VIN VKA I K (OFF) V REF R2 - TEST CIRCUIT 1 (VKA = VREF) - TEST CIRCUIT 2 (VKA > VREF) - TEST CIRCUIT 3 (OFF STATE CURRENT) Applications Information – Stability Selection of load capacitance when using L431L as a shunt regulator When the L431L is used as a shunt regulator, two options for selection of CL are recommended for optimal stability: 1. No load capacitance across the device, decouple at the load. 2. Large capacitance across the device, optional decoupling at the load. The reason for this is that L431L exhibits instability with capacitances in the range of 1nF to 1uf (approx.) at light cathode currents (up to 3mA typical). The device is less stable the lower the cathode voltage has been set for. Therefore while the device will be perfectly stable operating at a cathode current of 10mA with a 0.1uF capacitor across it, it will oscillate transiently during start-up as the cathode current passes through the instability region. Selecting a very low 3 (or preferably, no)capacitance, or alternatively a high capacitance (such as 10uF) will avoid this issue altogether. Since the user will probably wish to have local decoupling at the load anyway, the most cost effective method is to use no capacitance at all directly across the device. PCB trace/via resistance and inductance prevent the local load decoupling from causing the oscillation during the transient start-up phase. Note : if the L431L is located right at the load, so the load decoupling capacitor is directly across it, then this capacitor will have to be ≦ 100pF or ≧ 1uF. APR-25-2002 NIKO-SEM 1.24V Low-Voltage Adjustable Precision Shunt Regulator L431L Small-Signal Gain and Phase Shift VS. Frequency Test Circuit for Small Signal Gain and Phase OUT 15K Iz 3 1 1 1 10uF 232 L431L 2 8.25K 2 2 GND Test Circuit for Stability Stability Boundary Condition For Shunt Regulation VS. Cathode Current and Load Capacitance R 3 Iz R1 1 1 2 2 Cathode Current VS. Cathode Voltage CL L431L R2 Cathode Current VS. Cathode Voltage 4 APR-25-2002 1.24V Low-Voltage Adjustable Precision Shunt Regulator NIKO-SEM Reference Voltage VS. Junction Temperature L431L Ω Reference Impedance VS. Frequency Ratio of Delta Reference Voltage to Delta Cathode Voltage VS. Junction Temperature Reference Input Current VS. Junction Temperature ΔVref /ΔVz (-mV/V) ΔVz = 16V to Vref ∞ 5 APR-25-2002 NIKO-SEM 1.24V Low-Voltage Adjustable Precision Shunt Regulator L431L Off-State Cathode Current VS. Junction Temperature Reference Impedance rz (Ω) VS. Junction Temperature PIN CONFIGURATIONS 6 APR-25-2002 1.24V Low-Voltage Adjustable Precision Shunt Regulator NIKO-SEM L431L DEVICE SELECTION GUIDE Device L431LNB L431LM3B L431LVB L431LM5B Package TO-92 SOT-23-3 SOIC-8 SOT-23-5 Marking L431LN 1LM3 L431LV Tolerance 1% 1% 1% 1LM5 1% APPLICATION CIRCUIT P01N02LM or P3055L Niko Vin + D Vout S Cin G R1 5V or 12V + 1K Cout K + R A L431L Niko 10uF Vout = (1 + 7 R1 R2 R2 ) Vref APR-25-2002 NIKO-SEM 1.24V Low-Voltage Adjustable Precision Shunt Regulator L431L TO-92 MECHANICAL DATA Dimension mm Min. Typ. Dimension Max. mm Min. Typ. Max. 2.540 2.667 A 4.445 5.207 H 2.413 B 4.318 5.334 I 0.356 C 12.7 15.5 J D 0.356 0.533 K E 1.143 1.397 L F 3.175 4.191 M G 0.762 1.270 N 1.27 8 0.533 APR-25-2002 NIKO-SEM 1.24V Low-Voltage Adjustable Precision Shunt Regulator L431L SOT-23 (M3) MECHANICAL DATA Dimension mm Min. A Typ. Dimension Max. 0.95 Min. Typ. Max. H 0.10 0.15 0.25 0.37 B 2.60 2.80 3.00 I C 1.40 1.60 1.80 J D 2.70 2.90 3.10 K E 1.00 1.10 1.30 L F 0.00 0.10 M G 0.35 0.5 N 0.4 9 mm APR-25-2002 NIKO-SEM 1.24V Low-Voltage Adjustable Precision Shunt Regulator L431L SOIC-8 (D) MECHANICAL DATA Dimension mm Min. Typ. Dimension Max. mm Min. Typ. Max. A 4.8 5.0 H 0.4 1.27 B 3.8 4.0 I 0.18 0.25 C 5.8 6.2 J D 0.35 0.48 K E 1.27 F G 0.1 0.22 0° 8° L 1.65 M 0.25 N 10 APR-25-2002 NIKO-SEM 1.24V Low-Voltage Adjustable Precision Shunt Regulator L431L SOT-23 (M5) MECHANICAL DATA Dimension mm Dimension mm Min. Typ. Max. A 1.0 1.10 1.30 e A1 0.00 0.10 H 2.60 A2 0.70 0.80 0.90 L 0.37 b 0.35 0.40 0.50 C 0.10 0.15 0.25 D 2.70 2.90 3.10 E 1.40 1.60 1.80 11 Min. Typ. Max. 1.90(TYP) 2.80 3.00 APR-25-2002