基于TLVH431B的精度为 0.5% 的低电压宽工作电流范围可调精密并联稳压器

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　　1 Features

　　Low-Voltage Operation: Down to 1.24 V

　　Reference Voltage Tolerances at 25°C

　　0.5% for B Grade

　　1% for A Grade

　　1.5% for Standard Grade

　　Adjustable Output Voltage, VO = VREF to 18 V

　　Wide Operating Cathode Current Range:

　　100 μA to 70 mA

　　0.25-Ω Typical Output Impedance

　　–40°C to +125°C Specifications

　　TLVH432 Provides Alternative Pinouts for

　　SOT-23-3 and SOT-89 Packages

　　Ultra-Small SC-70 Package Offers 40%

　　Smaller Footprint than SOT-23-3

　　2 Applications

　　Adjustable Voltage and Current Referencing

　　Secondary Side Regulation in Flyback SMPSs

　　Zener Replacement

　　Voltage Monitoring

　　Comparator with Integrated Reference

　　3 Description

　　The TLVH431 and TLVH432 devices are low-voltage 3-terminal adjustable voltage references, with specified thermal stability over applicable industrial and commercial temperature ranges. Output voltage can be set to any value between VREF (1.24 V) and 18 V with two external resistors (see Figure 19). These devices operate from a lower voltage (1.24 V) than the widely used TL431 and TL1431 shunt-regulator references.

　　When used with an optocoupler, the TLVH431 and TLVH432 devices are ideal voltage references in isolated feedback circuits for 3-V to 3.3-V switching-mode power supplies. They have a typical output impedance of 0.25 Ω. Active output circuitry provides a very sharp turn-on characteristic, making the TLVH431 and TLVH432 devices excellent replacements for low-voltage Zener diodes in many applications, including on-board regulation and adjustable power supplies.

　　The TLVH432 device is identical to the TLVH431 device, but is offered with different pinouts for the

　　3-pin SOT-23 and SOT-89 packages.

　　TLVH431 is a low power counterpart to TL431, having lower reference voltage (1.24 V versus 2.5 V) for lower voltage adjustability and lower minimum cathode current (Ik(min)= 100 µA versus 1 mA). Like TL431, TLVH431 is used in conjunction with its key components to behave as a single voltage reference, error amplifier, voltage clamp or comparator with integrated reference.

　　TLVH431 is also a higher voltage counterpart to TLV431, with cathode voltage adjustability from 1.24 V to 18 V, making this part optimum for a wide range of end equipments in industrial, auto, telecom and computing. In order for this device to behave as a shunt regulator or error amplifier, >100 µA (Imin(max)) must be supplied in to the cathode pin. Under this condition, feedback can be applied from the Cathode and Ref pins to create a replica of the internal reference voltage.

　　Various reference voltage options can be purchased with initial tolerances (at 25°C) of 0.5%, 1%, and 1.5%. These reference options are denoted by B (0.5%), A (1.0%) and blank (1.5%) after the TLVH431.

　　The TLVH431xC devices are characterized for operation from 0°C to 70°C, the TLVH431xI devices are characterized for operation from –40°C to +85°C, and the TLVH431xQ devices are characterized for operation from –40°C to +125°C

　　TLVH431 consists of an internal reference and amplifier that outputs a sink current base on the difference between the reference pin and the virtual internal pin. The sink current is produced by an internal Darlington pair.

　　When operated with enough voltage headroom (≥ 1.24 V) and cathode current (Ika), TLVH431 forces the reference pin to 1.24 V. However, the reference pin can not be left floating, as it needs Iref ≥ 0.5 µA (see Specifications). This is because the reference pin is driven into an NPN, which needs base current in order operate properly.

　　When feedback is applied from the Cathode and Reference pins, TLVH431 behaves as a Zener diode, regulating to a constant voltage dependent on current being supplied into the cathode. This is due to the internal amplifier and reference entering the proper operating regions. The same amount of current needed in the above feedback situation must be applied to this device in open loop, servo or error amplifying implementations in order for it to be in the proper linear region giving TLVH431 enough gain.

Unlike many linear regulators, TLVH431 is internally compensated to be stable without an output capacitor between the cathode and anode. However, if it is desired to use an output capacitor Figure 15, Figure 16, and Figure 17 can be used as a guide to assist in choosing the correct capacitor to maintain stability.

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