SBAS945A February 2022 – July 2022 AMC23C14
PRODUCTION DATA
The voltage on the REF pin determines the trip threshold of window comparator 1. The internal precision current source forces a 100-μA current through an external resistor connected from the REF pin to GND1. The resulting voltage across the resistor (VREF) equals the magnitude of the positive and negative trip thresholds, see Figure 7-1. Place a 100-nF capacitor parallel to the resistor to filter the reference voltage. This capacitor must be charged by the 100-μA current source during power-up and the charging time may exceed the high-side blanking time (tHS,BLK). In this case, as shown in Figure 7-2, window comparator 1 may output an incorrect state after the high-side blanking time has expired until VREF reaches its final value. See the Section 7.3.5 section for more details on power-up behavior.
The voltage on the REF pin also determines the functionality of the negative comparators (Cmp1, Cmp3) and the hysteresis of the positive comparator (Cmp0) shown in the Section 7.2. If VREF exceeds the VMSEL threshold defined in the Electrical Characteristics table, both negative comparators (Cmp1 and Cmp3) are disabled and the hysteresis of Cmp0 is increased from 4 mV (typical) to 25 mV. Positive-comparator mode is intended for voltage-monitoring applications that require higher input voltages and higher noise immunity.
The reference pin can be driven by an external voltage source to change the comparator thresholds during operation. However, do not drive VREF dynamically across the VMSEL threshold during normal operation because doing so changes the hysteresis of the Cmp0 comparator and can lead to unintentional switching of the OUT1 output.
Figure 7-3 shows a mode selection timing diagram.