HI-8435PCT データシートの表示（PDF） - Holt Integrated Circuits

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HI-8435PCT

32-Channel Ground/Open or Supply/Open Sensor with SPI Interface

Holt Integrated Circuits 

HI-8435

FUNCTIONAL DESCRIPTION

OVERVIEW

The HI-8435 is comprised of 32 sensors arranged in 4

banks of 8 inputs, easily accessible via a four wire SPI

communication bus. Each bank of sensors can be

programmed as either GND/Open or Supply/Open. The

state of each sensor can be read out through the SPI.

The GND/Open high/low thresholds can be programmed

independently of the Supply/Open high/low thresholds.

Table 14 summarizes basic function selection and Table 16

gives more details on possible threshold values.

FUNCTION TABLE

Table 14. Function Table

SENSE_n

PSEN_n SO_n VWET_n

Open or > VTHI

L (GND/OPEN)

L

< VTLO

L (GND/OPEN)

H

Open or < VTLO

H (V+/OPEN)

H

> VTHI

H (V+/OPEN)

L

**

**

open

open

An internal test mode is available which sets the input to

each sensor comparator to the test value as programmed

by the Test Mode Data Register.

INITIALIZATION AND RESET

The HI-8435 generates a full reset upon application of

power. This power-on-reset (POR) sets all registers to their

default values.

The part can also be initialized to the full reset state by“

applying a 100ns active low pulse to the external MRB pin.

A software reset is also possible via the SPI by writing a “1’

to CNTRL<1>. This reset is the same as the full reset

except the part is held in the reset mode until the

CNTRL<1> bit is written back to a “0”.

H = VLOGIC, L = GND

VTHI = Threshold Center Value + ½ Hsyteresis

VTLO = Threshold Center Value - ½ Hysteresis

**For GND/Open applications VWETn must be set greater than

VTHI/0.9 + 2.25V

To program the thresholds:

a) Select VTHI and VTLO.

b) Hysteresis = VTHI - VTLO.

c) Center Value = (VTHI - VTLO)/2 X 2codes/V

= VTHI + VTLO codes

d) Program the register.

Example:

a) GND/Open, for VTHI = 10.5V and VTLO = 4.5V

b) Hysteresis = VTHI - VTLO = 10.5 - 4.5 = 6V = 0x06

c) Center Value = VTHI + VTLO = 15 codes = 0x0F

d) Program GOCENHYS register: 0x3A 0x06 0x0F

CONFIGURATION

The user configures the HI-8435 for specific applications by:

1) Programming the sensor type for each of the 4 banks.

2) Convert the required VTHI and VTLO into center and

hysteresis values as shown in example below.

3) For GND/Open sensors, VWETn must be set greater

than VTHI/0.9 + 2.25V.

PROGRAMMING THRESHOLDS

GND/OPEN SENSING

For GND/Open sensing, the PSENn bit is set to 0.

Referring to the Block Diagram, Figure 2, this selection will

connect a 3.3KΩ pull-up resistor through a diode to

VLOGIC. This resistor gives extra noise immunity for

detecting the open state while providing relay wetting

current. The user programs the desired

threshold/hysteresis levels and then determines the open

input voltage to set VWETn.

OPEN INPUT VOLTAGE

The HI-8435’s on-chip DAC takes the 6-bit programmed

center and hysteresis values from the Threshold Center

Value and Hysteresis Registers (GOCENHYS and

SOCENHYS) and converts them to VTHI and VTLO values.

Maximum and minimum values may be found in Table 16.

The gain of the DAC is 0.5V per bit.

VTHI = center value + ½ hysteresis

VTLO = center value - ½ hysteresis

For correct operation, the VSENSE_n when open, must be

higher than VTHI so SO_n will be low. This condition

requires VWET to be set greater than (VTHI/0.9 + 2.25V).

Various ARINC standards such as ARINC 763 define the

standard “Open” signal as characterized by a resistance of

100KΩ or more with respect to signal common. The user

should consider this 100KΩ to ground case when setting

the thresholds.

HOLT INTEGRATED CIRCUITS

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