When the cathode/output voltage or current of TL43xLI 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, TL43xLI will have the characteristics shown in Figure 18. With such high gain in this configuration, TL43xLI is typically used as a comparator. With the reference integrated makes TL43xLI the preferred choice when users are trying to monitor a certain level of a single signal. Look at SLVA987 for more details on open loop comparator applications on the TL431LI.