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器件3D模型￥ 115.313
HI-8425PCTF 数据手册 - HOLT
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HOLT
封装:
QFN
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HI-8425PCTF数据手册
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FUNCTIONAL DESCRIPTION
HOLT INTEGRATED CIRCUITS
4
SENSING
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.
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 and a 23.8K resistor through 3 diodes to VWET.
These resistors give extra noise immunity for detecting the
open state while providing relay wetting current. Configuring
Ω
HI-8425 (40 pin version) - THRESHOLD SELECT
The HI-8425 offers a choice between internally fixed
thresholds or external thresholds provided by the user.
GND/OPEN SENSING
.
, HI_SET/LO_SEL and VWET as described below
sets the window comparator thresholds, V and V , the
open 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
hysteresis levels.
For applications that can take advantage of the very small 32
pin chip scale package of the HI-8426, 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. This condition requires
VWET to be set greater than (VTHI/0.9 + 2.25V)
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
THS_SEL
THS_SEL
THI TLO
THI THLO
THI
TLO
SENSE_n
THI
With set to GND, the window comparator
thresholds are fixed based on an internal reference. The high
threshold, V , and the low threshold, V levels may be
found in Table 2. 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
V
. Various
ARINC standards such as ARINC 763 define t
THS_SEL
THS_SEL
HI-8426 (32 pin version) THRESHOLD SELECT
OPEN INPUT VOLTAGE
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 higher 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_SEL
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. The VWET
pin must be left open in the Supply/Open sensing case.
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
THLO
SENSE_n WET
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
Table 1. Function Table
HI-8425, HI-8426
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