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HI-8431PQI Datasheet(PDF) 4 Page - Holt Integrated Circuits |
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HI-8431PQI Datasheet(HTML) 4 Page - Holt Integrated Circuits |
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4 / 18 page  FUNCTIONAL DESCRIPTION HOLT INTEGRATED CIRCUITS 4 SENSING For GND/Open sensing, the SNS_SEL pin is connected to GND Referring to the Block Diagram, Figure 2, this selection will connect a 3.3K pull-up resistor through a diode to VLOGIC These resistors give extra noise immunity for detecting the open state while providing relay wetting current. Configuring Ω HI-8430 (40 pin version) - THRESHOLD SELECT The HI-8430 offers a choice between internally fixed thresholds or external thresholds provided by the user. The 8 Sense Channels can be configured to meet the requirements of a variety of conditions and applications. Table 1 summarizes basic function selection and Table 2 gives more details on possible threshold values. and a 23.8K resistor through 3 diodes to VWET. hysteresis levels. For applications that can take advantage of the very small 32 pin chip scale package of the HI-8431, is not available and an internal pull-up makes it mandatory to supply HI_SET and LO_SET externally. For correct operation, the V when open, must be higher than so SO_n will be low. In the case of 3.3V VLOGIC operation, VWET be connected to a supply greater than (1.3 x VTHI + 2.25V) to fulfill the above condition. In the case of 5V operation, the above condition may be satisfied with VWET left open (see table 2). In this case, the input floats to V = he standard “Open” signal as characterized by a resistance of 100K or more with respect to signal common. The user should consider this 100K to ground case when setting the thresholds. Ω Ω Ω The high threshold, V , and the low threshold, V levels may be found in Table 2. V VLOGIC - 0.75V. Various ARINC standards such as ARINC 763 define t THI TLO SENSE_n THI HI-8431 (32 pin version) THRESHOLD SELECT THS_SEL OPEN INPUT VOLTAGE NOTE 1: NOTE 2: must SENSE_n GND/OPEN SENSING . , HI_SET/LO_SET and VWET as described below sets the window comparator thresholds, V and V , the input voltage when open, and the input current. is equal to 10X the voltage on the HI_SET pin. is equal to 10X the voltage on the LO_SET pin. This mode allows the user complete flexibility to define the thresholds and THS_SEL THI TLO With set to GND, the window comparator thresholds are fixed based on an internal reference. When the internal references are used the HI_SET and LO_SET pins should be connected to GND. For applications with either large GND offsets or thresholds higher than VLOGIC - 0.75V, is set high and the thresholds are set externally, for example by a simple resistor divider off the VLOGIC supply. In this case V V THS_SEL THS_SEL THI TLO WETTING CURRENT THRESHOLD SELECT WETTING CURRENT For GND/Open applications with VWET open, the wetting current with the input voltage at GND is simply (VLOGIC - 0.75)/3.3K. When applying a voltage at the VWET pin the wetting current is (VLOGIC - 0.75)/3.3K + (VWET - 4.2)/127K. Additional wetting current can be achieved by placing an external resistor and a diode between VWET and the individual sense inputs. The 8 Sense Channels can be configured to sense Supply/Open by connecting the SNSE_SEL pin to VLOGIC. Refering to Figure 2, a 32K resistor is switched in series to provide a pull down in addition to the 400K of the comparator input divider to GND. Similar to the GND/Open case configuring , HI_SET/LO_SET and VWET as described below sets the window compara- tor thresholds, the open input voltage when open and the wetting current. The threshold selections are handled in the same way as stated above for the GND/OPEN case. For set low, the internal reference nominally sets the window comparator. See table 2 for the For set high, the final thresholds are 10X the voltage set on the HI_SET and LO_SET pins. For the Supply/Open case the wetting current into the sense input is the current sunk by the effective 28K to GND. For V = 28V, I is 1ma. See Figure 12. SUPPLY/OPEN SENSING Ω Ω Ω THS_SEL THS_SEL THS_SEL V and V threshold levels. THI TLO SENSE_n WET The VWET pin must be left open in the Supply/Open sensing case. SENSE_n SNSE_SEL OE SO_n Open or > VTHI L (GND/OPEN) L L < VTLO L (GND/OPEN) L H X L (GND/OPEN) H Z Open or < VTLO H (V+/OPEN) L H > VTHI H (V+/OPEN) L L X H (V+/OPEN) H Z H = VLOGIC, L = GND, Z = Hi-Z, X = Don’t Care, V+ = V See Table 2 for values of VTHI/VTLO SUPPLY HI-8430, HI-8431 Table 1. Function Table |
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