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ATL431LI_V02 Datasheet(Hoja de datos) 12 Page - Texas Instruments

No. de Pieza. ATL431LI_V02
Descripción  ATL431LI / ATL432LI High Bandwidth Low-Iq Programmable Shunt Regulator
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Fabricante  TI1 [Texas Instruments]
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Copyright © 2017–2019, Texas Instruments Incorporated
10.3 Feature Description
ATL431LI consists of an internal reference and amplifier that outputs a sink current based on the difference
between the reference pin and the virtual internal pin. The sink current is produced by the internal Darlington
pair, shown in the above schematic (Figure 21). A Darlington pair is used in order for this device to be able to
sink a maximum current of 15 mA.
When operated with enough voltage headroom (
≥ 2.5 V) and cathode current (IKA), ATL431LI forces the
reference pin to 2.5 V. However, the reference pin can not be left floating, as it needs IREF ≥ 0.4 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, ATL431LI 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 ATL431LI enough gain.
Unlike many linear regulators, ATL431LI 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 13 can be used as a
guide to assist in choosing the correct capacitor to maintain stability.
10.4 Device Functional Modes
10.4.1 Open Loop (Comparator)
When the cathode/output voltage or current of ATL431LI is not being fed back to the reference/input pin in any
form, this device is operating in open loop. With proper cathode current (Ika) applied to this device, ATL431LI will
have the characteristics shown in SLVA987. With such high gain in this configuration, ATL431LI is typically used
as a voltage comparator. The integrated voltage reference makes the ATL431LI a flexible device for monitoring a
signal for undervoltage and overvoltage detection.
10.4.2 Closed Loop
When the cathode/output voltage or current of ATL431LI is being fed back to the reference/input pin in any form,
this device is operating in closed loop. The majority of applications involving ATL431LI use it in this manner to
regulate a fixed voltage or current. The feedback enables this device to behave as an error amplifier, computing
a portion of the output voltage and adjusting it to maintain the desired regulation. This is done by relating the
output voltage back to the reference pin in a manner to make it equal to the internal reference voltage, which can
be accomplished via resistive or direct feedback.

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