TL431ACDR Integrated Circuits (ICs)

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1. Describe

TL431LI / TL432LI are pin-to-pin replacements of TL431ACDR / TL432. TL43xLI provides better stability, lower temperature drift (VI(dev)) and lower reference current (Iref) to improve system accuracy. TL431 and TL432 devices are three-terminal Adjustable shunt regulator with specified thermal Stability exceeds applicable automotive, commercial and Military temperature range. The output voltage can be Set to any value between Vref (approximately 2.5 V) and 36 V, with two external resistors. These The typical output impedance of the device is 0.2 Ω. Active output circuit provides very fast turn-on Features that make these devices excellent Replaces Zener diodes in many applications, Such as on-board adjustment, adjustable power Power supply and switching power supply. TL432 The device has exactly the same functions and The electrical specifications are the same as the TL431 device, but with Different pinouts of DBV, DBZ and PK packages. Both TL431 and TL432 devices are Three levels, the initial tolerance (25°C) is 0.5%, 1% and 2%, for B, A and standard grades, respectively. In addition, low output drift and Temperature ensures good stability of the whole process temperature range. TL43xxC equipment is characterized by operation From 0°C to 70°C, TL43xxI devices are The operating temperature range is –40°C to 85°C, and TL43xxQ equipment is characterized by operation From –40°C to 125°C.

2. Feature

    1. Reference voltage tolerance at 25°C

        – 0.5% (Grade B)

        – 1% (Grade A)

        – 2% (standard grade)

    2. Adjustable output voltage: Vref to 36 V

    3. Operating temperature is −40°C to 125°C

    4. Typical temperature drift (TL43xB)

        – 6 mV (C temperature)

        – 14 mV (I temperature, Q temperature)

    5. Low output noise

    6. 0.2Ω typical output impedance

    7. Sink current capability: 1 mA to 100 mA

3. Application

    1. Adjustable voltage and current reference

    2. Secondary side regulation in flyback SMPS

    3. Zener replacement

    4. Voltage monitoring

    5. Comparator with integrated reference

4. Pin configuration

5. Function Description

TL431ACDR is composed of internal reference and amplifier. The amplifier outputs a sink current reference pin and a virtual internal pin based on the difference between the two. The absorption current is generated by the internal Darlington pair. The Darlington pair is used to enable the device to receive a maximum current of 100 mA. When operating with sufficient voltage headroom (≥ 2.5 V) and cathode current (IKA), the TL431 will force the reference pin voltage to 2.5 V. However, the reference pin cannot be left floating because it requires IREF ≥ 4 µA. This is because the reference pin is driven to npn, which requires base current to work properly. When feedback is applied from the cathode and the reference pin, the TL431ACDR acts as a Zener diode, and the adjustment depends on the constant voltage of the current supplied to the cathode. This is due to the internal amplifier And refer to the correct operating area. The amount of current required for the above feedback is the same This situation must be applied to the equipment in the open loop, servo or error amplification implementation so that it In the proper linear region, it provides enough gain for TL431ACDR. Unlike many linear regulators, the TL431ACDR does not require an output capacitor to perform internal compensation to maintain a stable cathode and anode gap. However, if necessary, use an output capacitor.

6. Device function mode

1. Open loop (comparator)

When the cathode/output voltage or current of the TL431ACDR is not fed back to the reference/input pin under any circumstances, the device works in open loop mode. After applying the appropriate cathode current (Ika) to the device. With such a high gain in this configuration, the TL431ACDR is usually used as a comparator.

2. closed loop

When the cathode/output voltage or current of the TL431ACDR is fed back to the reference/input pin in any form, the device works in a closed loop. Most applications involving TL43xx use it in this way to adjust a fixed voltage or current. Feedback enables the device to act as an error amplifier, calculating a portion of the output voltage and adjusting it to maintain the required adjustment. This is achieved by associating the output voltage back to the reference pin in some way, making it equal to the internal reference voltage, which can be achieved through resistance or direct feedback.